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Parks, Recreation & Tourism Management
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Current: About
Faculty and Staff Profile
Robert Powell
George B. Hartzog, Jr. Endowed Professor
Director Institute for Parks
Office: 100-4 Sirrine Hall
Email: RBP@clemson.edu
Ph.D. Forestry and Environmental Studies
Yale University 2005
M.E.M. Environmental Management
B.A. Interdiscplinary Studies
Univ. of North Carolina-Chapel Hill 1983
Department of Parks, Recreation and Tourism Management, Clemson University.
PRTM 2700: Introduction to Resource Recreation Management (2020-present)
PRTM 403: Elements of Park Planning (2006-2018)
PRTM 430/630: World Geography of Parks and Equivalent Reserves (2006-2020)
PRTM 201: The Recreation Environment (2005-2006)
PRTM 900: Integrated Conservation and Development Graduate Seminar (2012)
PRTM 900: Interdisciplinary Park and Protected Area Management: Questioning the Parks as Islands Approach Graduate Seminar (2008)
PRTM 900: Graduate Conservation Reading Seminar (2013-2014)
PRTM 298: Creative Inquiry (Undergraduate Research): Managing Recreation in the Clemson Experimental Forest (2006)
PRTM 891: Independent Study (2007-present)
PRTM 991: Doctoral Research (2007-present)
National Scholars Program, Clemson University.
PRTM 391 Honors: Values of Parks. (Seminar and Maymester Study Abroad Course in Grand Canyon National Park)(2016)
PRTM 398 Honors: Exploring Tiger Conservation in Bhutan (Seminar and Maymester Study Abroad Course)(2014)
PRTM 498 Honors: Values of Parks. (Seminar and Maymester Study Abroad Course in Grand Canyon and Zion National Parks)(2010)
Department of Forestry and Environmental Conservation; Clemson University.
FOR 431/431L; 631/631L: Recreation Resource Planning in Forest Management (2007-present)
FOR 991: Doctoral Research (2009-present)
Robert B. Powell is the George B. Hartzog, Jr. Endowed Professor in Philosophy, Parks, and Environmental Ethics in the Department of Parks, Recreation, and Tourism Management at Clemson University. He is also the Director of the Institute for Parks, which is an interdisciplinary institute focused on providing research, training, and outreach to support park and protected area management. With graduate degrees from Yale University, his research and outreach program has taken him to over 40 countries and 6 continents and focuses on environmental education/interpretation, ecotourism, protected areas, and the human dimensions of biodiversity conservation.
Include: environmental education and interpretation, parks and protected area management, ecotourism, outdoor recreation, and biodiversity conservation.
External Grants:
2022-2026 US National Park Service ($937,213) What leads to better outcomes in National Park Service interpretation? PI: MJ Stern (Virginia Tech). Co-PI: R.B. Powell
2022-2023 US National Forest Service ($36,165) El Yunque National Forest: Research to support regional community-based tourism and resilience. PI: R.B. Powell
2021-2023 US National Park Service ($199,547) Research to evaluate the National Park Service's Interpretation and Education Planning Processes. PI: R.B. Powell
2020-2022 National Park Foundation ($160,000). Building a culture of and capacity for evaluation in Environmental Education in National Parks. PI: MJ Stern (Virginia Tech). Co-PIs: R.B. Powell, Frensley, B.T. (UNC-W).
2019-2023 National Science Foundation. Advancing Informal STEM Learning (AISL) Research in Service to Practice Grant ($1.944M). What leads to better outcomes in informal STEM-based environmental education programs for youth? PI: R.B. Powell; Co-PI: M.J. Stern (Virginia Tech), B.T. Frensley (UNC-W), & R. Gagnon (Clemson Univ.)
2019-2021 Pisces Foundation ($150,000). Building a culture of and capacity for evaluation in Environmental Education: 2.0. Principal Investigator: Charlotte Clark, Duke Univ. Collaborator: R.B. Powell.
2018-2020 US National Park Service ($165,345). Research to evaluate visitor characteristics across and within seasons at Joshua Tree National Park. Co-Principal Investigators: Ryan Sharp, Kansas State Univ.; M. Brownlee, Clemson Univ., R.B. Powell.
2017-2018 North Carolina Outward Bound ($5,000). Assessing the Efficacy of the North Carolina Outward Bound Educator Initiative. Principal Investigator: R.B. Powell. Graduate Student: Hunter Holland
2016-2019 Institute for Museum and Library Services. ($487,000) Identifying the drivers of success in educational programs at nature centers and National Parks in the United States. Co-Principal Investigators: M.J. Stern (Virginia Tech) & R.B. Powell
2016-2018 National Science Foundation ($300,000) Advancing Informal STEM Learning (AISL) Pathways Grant.Methods development for systematic investigation of factors driving outcomes in informal STEM environmental education programs. Co-Principal Investigators: R.B. Powell & M.J. Stern (Virginia Tech).
2016-2017 Storer Foundation ($30,000) Assessing the Benefits of Outdoor Recreation. Principal Investigator: R.B. Powell, Collaborators: C. Monz (Utah State) and J. E. Thomsen (Univ. Montana).
2015-2016 Antarctica visitor study in cooperation with Aurora Expeditions. Principal Investigator: R.B. Powell.
2015-2016 Government of Viet Nam, Ministry of Construction. (Consultant) 2030 Plan for the Dong Van Stone Plateau Global Geopark in Ha Giang Province, Viet Nam. Principal Investigator: J. Spencer (Clemson). Collaborator: R.B. Powell.
2014-2015 Wildlife Management Institute ($139,495) Interactive Conservation Planning for the Appalachian Landscape Conservation Cooperative. PI: R. Baldwin (Clemson). Collaborator: R.B. Powell.
2013-2015 US National Park Service ($127,913). Goal setting and needs assessment for Interpretation and Education in the National Park Service. Co-principal Investigators: R.B.Powell & B. A. Wright (Clemson).
2014 Antarctica visitor study in cooperation with Aurora Expeditions. Principal Investigator: R.B.Powell.
2008-2013 National Audubon Society. ($506,000) Research for the evaluation and adaptive management of Toyota TogetherGreen. Co-principal Investigators: R.B. Powell, M.J. Stern (Virginia Tech), & N. Ardoin, (Stanford Univ.).
2011-2013 South Florida National Parks Trust ($60,130). Evaluation and research of environmental education at Everglades National Park. Co-principal Investigators: R.B.Powell, G. Ramshaw (Clemson), & M.J. Stern (Virginia Tech).
2009-2013 US National Park Service ($128,688). Assessing the health of Interpretation and Education in the National Park Service. Co-principal Investigators: M.J. Stern (Virginia Tech) & R.B.Powell.
2010-2012 National Parks Conservation Association: Center for Park Management ($219,368). Assessing quality indicators for interpretive programs in the National Park Service. Co-principal Investigators: M.J. Stern (Virginia Tech) & R.B.Powell.
2008-2012 US National Park Service ($24,600). Evaluation of curriculum-based environmental education programs at Great Smoky Mountains National Park. Co-principal Investigators: R.B.Powell & M.J. Stern (Virginia Tech).
2008-2011 US National Park Service and Friends of the Great Smoky Mountains National Park ($155,600). Research for sustainable adaptive management of environmental education and outreach at Great Smoky Mountains National Park. Co-principal Investigators: M.J. Stern (Virginia Tech) & R.B.Powell.
2007 USAID Sustainable Coastal Tourism in Asia-Sri Lanka: Overcoming governance barriers to integrated coastal, marine protected area, and tourism management. Principal Investigator: R.B. Powell.
2007-10 US National Park Service Wilderness Stewardship & Recreation Management Division ($70,000). Evaluation of wilderness recreational ethics education on public lands. Co-principal Investigators: R.B.Powell & B. A. Wright (Clemson University).
90) Kiewra, L.A., Powell, R.B., Stern, M.J., & Hemby, T. (In press) Is naturalness associated with positive learning outcomes during environmental education field trips? Journal of Environmental Education. DOI: 10.1080/00958964.2022.2157369
89) Powell, R.B., Stern, M.J., & Frensley, B.T. (2022) Which approaches are associated with better outcomes? Evidence from a national study of EE field trip programs. Environmental Education Research. DOI: 10.1080/13504622.2022.2145270
88) Ogletree, S.S., Larson, L.R., Powell, R.B., White, D., & Brownlee, M.T.J. (2022) Urban greenspace linked to lower crime risk across 301 major U.S. cities. Cities 131, 103949. DOI: 10.1016/j.cities.2022/103949
87) Woods, L.B.*, Powell, R.B., Stern, M.J., Frensley, B.T., & Wright, B.A. (2022) Reorienting training in the time of Covid-19 and social justice movements. 21(3), 302-318. Applied Environmental Education and Communication. DOI: 10.1080/1533015X.2022.2078439
86) Anderson, K., Stern, M.J., & Powell, R.B. (2022) Identifying areas and approaches for improving evaluation processes in environmental education in the United States of America. Journal of Environmental Education. 53(5), 290-303. DOI: 10.1080/00958964.2022.2122918
85) Frensley, B.T., Stern, M.J., Powell, R.B., & Sorice, M.G. (2022) Investigating the links between student basic psychological needs, engagement, and environmental literacy at a residential environmental education center. Journal of Environmental Education, 53:4, 186-198. DOI:10.1080/00958964.2022.2081654
84) Anderson, K., Stern, M.J., Powell, R.B., Dare, A.A., & Archibald, T. (2022) Culturally responsive evaluation and its application in environmental education. Evaluation and Program Planning, 92, 102073. DOI: 10.1016/j.evalprogplan.2022.102073
83) Frensley, B.T., Stern, M.J., Powell, R.B., & Blackwell, M.J. (2022) Exploring the links between teaching approaches and student outcomes at a residential setting. Environmental Education Research, 28(6), 826-844. DOI: 10.1080/13504622.2022.2044454
82) Holland, W.H.*, Powell, R.B., Holland, K.K., Garst, B.A., Baldwin, E.D., & Quigley, C.F. (2022) Experiential Wilderness-based Professional Development: Beliefs and Confidence of Participant Educators. Journal of Experiential Education, 45(2) 117-135. DOI: 10.1177/10538259211045385
81) Sabuhoro, E.*, Wright, B.A., Munanura, I. E., Powell, R. B., Hallo, J.C., & Layton P. (2021) Exploring the impact of community conservation enterprises on household livelihoods around two wildlife areas in Sub-Saharan Africa. Journal of Human Dimensions of Wildlife. DOI: 10.1080/10871209.2021.2015487
80) Jamaliah, M. M., Mgonja, J. T., Alazaizeh, M. M., & Powell, R. B. (2021). How does interpretive tour guiding promote tourists' pro-environmental behaviour? Evidence from Tanzania. Tourism Recreation Research. DOI: 10.1080/02508281.2021.1992953
79) Stern, M.J., Powell, R.B., & Frensley, B.T. (2022) How do environmental education field trips for adolescent youth in the United States influence audiences of different grade level, race, and socioeconomic class? Environmental Education Research. 28(2), 197–215. DOI: 10.1080/13504622.2021.1990865
78) Stern, M.J., Powell, R. B. & Frensley, B.T. (2022) Interpretation and environmental education research on public lands: Lessons learned and new directions. Journal of Parks and Recreation Administration, 40(1), 228–237. DOI: 10.18666/JPRA-2021-11003
77) Merritt, E., Stern, M.J., Powell, R. B., & Frensley, B.T. (2022) A systematic literature review to identify evidence-based principles to improve online environmental education. Environmental Education Research, 28(5),674-694. DOI: 10.1080/13504622.2022.2032610
76) Holland, K.*, Larson, L., Powell, R.B., Holland, W., Allan, L., Nabaala, M., Tome, S., Seno, S., & Nampushi, J. (2022). Impacts of Tourism on Support for Conservation, Local Livelihoods, and Community Resilience around Maasai Mara National Reserve, Kenya. Journal of Sustainable Tourism. 30(11) 2526-2548. DOI: 10.1080/09669582.2021.1932927
75) Stern, M.J., & Powell, R. B. (2021) Taking stock of interpretation research: Where have we been and where are we heading? Journal of Interpretation Research. 25(2), 65-87. DOI:10.1177/10925872211023205
74) Pratson, D.F.*, Stern, M.J., & Powell, R.B. (2021) What organizational factors motivate environmental educators to perform their best? Journal of Environmental Education, 52(4), 256-271.
73) Kitheca, B. M.*, Baldwin, E., & Powell, R.B. (2021) Grey to green: Tracing the path to environmental transformation and regeneration of a major industrial city. Cities: The International Journal of Urban Policy and Planning 108. DOI:10.1016/j.cities.2020.102987
72) Holland, W.H.*, Powell, R.B. & Holland, K.K.* (2020) Wilderness-based professional development for teachers: Exploring outcomes and influential programmatic elements. Journal of Outdoor Recreation, Education, and Leadership, 12(4), 380-396. DOI:10.18666/JOREL-2020-V12-I4-10271
71) O'Hare, A.,* Powell, R.B., Stern, M.J., & Bowers, E.P. (2020) Influence of educator's emotional support behaviors on environmental education student outcomes. Journal of Environmental Education Research, 26 (11), 1556-1577. DOI:10.1080/13504622.2020.1800593
70) Stern, M.J. & Powell, R.B. (2020) Field trips and the experiential learning cycle. Journal of Interpretation Research. 25(1), 46–50. DOI:10.1177/1092587220963530
69) Powell, R.B., Miller, Z.D., & Stern, M.J. (In press) The role of education and communications in proactively and adaptively managing visitor use of parks and protected areas. In Visitor Use Management in Parks and Protected Areas: Traditions, Approaches, and Possibilities. Edited by Brownlee, M.T.J., Sharp, R., Miller, Z.D. & Others. Sagamore Venture Publishing, Champaign, IL.
68) Lee, H.*, Stern, M.J., & Powell, R.B. (2020) Assessing the influence of preparation and follow-up on student outcomes associated with environmental education field trips. Journal of Environmental Education Research, 26 (7), 989–1007. DOI:10.1080/13504622.2020.1765991
67) Dale, R.G.*, Powell, R.B., Stern, M.J., & Garst, B.A. (2020) Influence of the natural setting on environmental education student outcomes. Journal of Environmental Education Research 26(5), 613-631. DOI: 10.1080/13504622.2020.1738346
66) Sabuhoro, E.*, Wright, B.A,. Powell, R.B., Hallo, J.C., Layton, P., & Munanura, I.E. (2020) Perceptions and behaviors of indigenous populations regarding illegal use of park resources in the Greater Virunga Transboundary Landscape. Environmental Management 65, 410-419. DOI:10.1007/s00267-020-01254-z
65) Frensley, B.T.*, Stern, M.J., & Powell, R.B. (2020) Does student enthusiasm equal learning? The mismatch between observed and self-reported student engagement and environmental literacy outcomes in a residential setting. Journal of Environmental Education 51(6), 449-461. DOI:10.1080/00958964.2020.1727404
64) Jamaliah, M.M.*, Powell, R.B., & Sirima, A.* (2021) Climate change adaptation and implementation barriers: A qualitative exploration of managers of Dana Biosphere Reserve-ecotourism system. Journal of Ecotourism, 20(1), 18-34. DOI:10.1080/14724049.2020.1746320
63) Poncet, S., Wolfaardt, A.C., Barbraud, C., Arriegas, R.A., Black, A., Powell, R.B. & Phillips, R.A. (2020) The distribution, abundance, status and global importance of giant petrels (Macronectes giganteus and M. halli) breeding at South Georgia. Polar Biology 43, 17–34. DOI:10.1007/s00300-019-02608-y
62) Citarella, M.M.*, Hallo, J.C., Fefer, J.P., Brownlee, M.T.J., Powell, R.B. & Dudley, K. (2019) Taking the plunge: Enhancing the visitor experience in waterfall-based state parks. Journal of Park and Recreation Administration, 37(3), 70-88. DOI:10.18666/JPRA-2019-9149
61) Ogletree, S.S.*, Powell, R.B., Baldwin, R. F. & Leonard, P.B. (2019) A framework for mapping cultural resources in landscape conservation planning. Conservation Science and Practice, 1(6). DOI:10.1111/csp2.41
60) Clark, M., Wilkins, E., Dagan, D.T., Powell, R.B., Sharp, R.L., & Hillis, V. (2019) Bringing forecasting into the future: Using Google to predict visitation in U.S. National Parks. Environmental Management, 243, 88-94. DOI: 10.1016/j.jenvman.2019.05.006
59) Powell, R.B., Stern, M. J., Frensley, B.T., & Moore, D. (2019) Identifying and developing crosscutting environmental education outcomes for adolescents in the 21st Century (EE21). Environmental Education Research, 25(9), 1281-1299. DOI:10.1080/13504622.2019.1607259
58) Miller, Z.D.*, Freimund, W.A., Metcalf, E.C., Nickerson, N.P. & Powell, R.B. (2019) Merging elaboration and the theory of planned behavior to understand bear spray behavior of day hikers in Yellowstone National Park. Journal of Environmental Management, 63, 366–378. DOI:10.1007/s00267-019-01139-w
57) Holland, K.E.*, Larsen, L., & Powell, R.B. (2018) Characterizing conflict between humans and big cats Panthera spp: A systematic review of research trends and management opportunities. PlosOne 13(9):e0203877. https://doi.org/10.1371/journal.pone.0203877
56) Holland, W.H.*, Powell, R.B., Thomsen, J.M., and Monz, C.A. (2018) A systematic review of the psychological, social, and educational outcomes associated with participation in wildland recreational activities. Journal of Outdoor Recreation, Education, and Leadership,10(3), 197-225. DOI:10.18666/JOREL-2018-V10-I3-8382
55) Munanura, I.E.*, Backman, K.F., Hallo, J.C, Powell, R.B., & Sabuhoro, E. (2018) Understanding the relationship between livelihood constraints of poor forest-adjacent residents and illegal forest use at Volcanoes National Park, Rwanda. Conservation and Society, 16(3), 291-304. DOI:10.4103/cs.cs_14_83
54) Miller, Z.D.*, Freimund, W., & Powell, R.B. (2018) Measuring elaboration and evaluating its influence on behavioral intentions. Journal of Interpretation Research, 23(1), 27-44.
53) Munanura, I.E.*, Backman, K.F., Sabuhoro, E., Powell, R.B., & Hallo, J.C. (2018) The perceived forms and drivers of forest dependence at Volcanoes National Park, Rwanda. Environmental Sociology, 4(3), 343-357. DOI: 10.1080/23251042.2017.1414661
52) Thomsen, J.M., Powell, R.B., and Monz, C.A. (2018) A systematic review of the physical and mental health benefits of wildland recreation. Journal of Parks and Recreation Administration, 36(1), 123-148. DOI:10.18666/JPRA-2018-V36-I1-8095
51) Jamaliah, M.M.* & Powell, R.B. (2019) Integrated vulnerability assessment of ecotourism to climate change in the Dana Biosphere Reserve, Jordan. Current Issues in Tourism, 22(14), 1705-1722. DOI: 10.1080/13683500.2017.1401982
50) Morris, D.M.*, Pilcher, J.J., & Powell, R.B. (2017). Task dependent cold stress during expeditions in Antarctic environments. International Journal of Circumpolar Health, 76(1),1379306. DOI:10.1080/22423982.2017.1379306
49) Powell, R.B., Stern, M.J., & Frensley, B.T.* (2020) Identifying outcomes for environmental education at national parks. In Thompson, J.L. & Houseal, A.K. (editors). America's largest classrooms: What we learn from our national parks (pp-245-258). Univ. of CA Press, Oakland, CA.
48) Powell, R.B., Depper, G.L.*, & Wright, B.A. (2018) Interpretation training needs in the 21st Century: A needs assessment of interpreters in the National Park Service, Journal of Interpretation Research. 22(2),17-34. DOI: 10.1177/109258721702200203
47) Jamaliah, M.M.* & Powell, R.B. (2018) Ecotourism resilience to climate change in the Dana Biosphere Reserve, Jordan. Journal of Sustainable Tourism, 26(4), 519-536. DOI:10.1080/09669582.2017.1360893
46) Powell, R. B., Vezeau, S.L.*, Stern, M.J., Moore, D.D., & Wright, B.A. (2018) Does interpretation influence elaboration and environmental behaviors? Journal of Environmental Education Research, 24(6), 875-888. DOI:10.1080/13504622.2017.1339302
45) Powell, R.B., Green, T., Holladay, P.J., Krafte, K.*, Duda, M.*, Nguyen, M.T., Spencer, J.H., & Das, P. (2018) Examining community resilience to assist in sustainable tourism development planning in Dong Van Karst Plateau Geopark, Viet Nam. Tourism Planning and Development,15(4), 436-457. DOI:10:1080/21568316.2017.1338202
44) Stern, M.J., Frensley, B.*, Powell, R.B., & Ardoin, N.M. (2018) What difference do role models make? Investigating outcomes at a residential environmental education center. Environmental Education Research, 24(6), 818-830. DOI: 10.1080/13504622.2017.1313391
43) Holladay, P.J.*, & Powell, R.B. (2016) Social-ecological resilience and stakeholders: A qualitative inquiry into community-based tourism in the Commonwealth of Dominica. Caribbean Studies, 44(1), 3-28. DOI: 10.1353/crb.2016.0000
42) Munanura, I.E.*, Backman, K.F., Hallo, J, & Powell, R.B. (2016) Perceptions of tourism revenue sharing impacts on Volcanoes National Park, Rwanda: A sustainable livelihoods framework. Journal of Sustainable Tourism, 12, 1709-1726. DOI: 10.1080/09669582.2016.1145228
41) Stern, M.J., Ardoin, N.M., & Powell, R.B. (2016) Exploring the effectiveness of community outreach strategies: The case of the Audubon Toyota TogetherGreen program. Society and Natural Resources, 30(1) 95-111.
40) Vezeau, S.L., Powell, R. B., Stern, M.J., Moore, D., & Wright, B.A. (2017) Development and validation of two scales for measuring elaboration and behaviors associated with stewardship in children. Environmental Education Research, 23(2) 192-213. DOI:10.1080/13504622.2015.1121377
39) Sgalitzer, H.A.*, Brownlee, M.T.J., Bricker, K.S., & Powell, R.B. (2016) Modelling travelers' philanthropy: Tourists' motivations to donate at Sweetwater Chimpanzee Sanctuary. Journal of Ecotourism, 15(1), 1-20. DOI: 10.1080/14724049.2015.1117091
38) Skibins, J.C.*, Powell, R.B., & Hallo, J.C. (2016) Lucky 13: Conservation implications of broadening 'Big 5' flagship species recognition in East Africa. Journal of Sustainable Tourism, 24(7), 1024-1040. DOI:10.1080/09669582.2015.1101126
37) Powell, R.B., Ramshaw, G.P., Ogletree, S.S.*, & Krafte, K.* (2016) Can heritage resources highlight changes to the natural environment caused by climate change? Evidence from the Antarctic tourism experience. Journal of Heritage Tourism, 11(1), 71-87. DOI:10.1080/1743873X.2015.1082571
36) Depper, G.L.*, Vigil, D.C., Powell, R.B. & Wright, B.A. (2015-2016) Resource protection, visitor safety, and employee safety: How prepared is the National Park Service? Park Science, 32(2) 18-24.
35) Brownlee, M.T.J.*, Hallo, J.C., Jodice, L.W., Moore, D.D., Powell, R.B., & Wright, B.A. (2015) Place attachment and marine recreationists' attitudes towards offshore wind energy development. Journal of Leisure Research, 47(2), 263-284. DOI:10.1080/00222216.2015.11950360
34) Munanura, I.E.*, Backman, K., Moore, D., Hallo, J., & Powell, R.B. (2014) Household poverty dimensions influencing forest dependence at Volcanoes National Park, Rwanda: An application of the sustainable livelihoods framework. Natural Resources, 5(16), 1031.
33) Miller, Z.D.*, Hallo, J.C., Sharp, J.L., Powell, R.B., & Lanham, J.D. (2014) Birding by ear: A study of recreational specialization and soundscape preference. Human Dimensions of Wildlife, 19(6), 498-511. DOI: 10.1080/10871209.2014.921845
32) Vagias, W.M.*, Powell, R.B., Moore, D.D., & Wright, B.A. (2014) Predicting behavioral intentions to comply with recommended Leave No Trace practices. Leisure Sciences, 38(5), 439-445. DOI:10.1080/01490400.2014.912168
31) Stern, M.J., Powell, R.B., & Hill, D. (2014) Environmental education research in the new millennium: What do we measure and what have we learned? Environmental Education Research, 20(5), 581-611. DOI:10.1080/13504622.2013.838749
30) Brownlee, M.T.J.*, Hallo, J.C., Moore, D.D., Powell, R.B., & Wright, B.A. (2014) Attitudes toward water conservation: The influence of site specific factors and beliefs in climate change. Society and Natural Resources, 27(9), 964-982. DOI:10.1080/08941920.2014.929768
29) Thomsen, J.M.*, Powell, R.B., & Allen, D. (2013) What is the value and implications of viewing park resources as health resources? Park Science, 30(2), 30-36.
28) Stern, M.J. & Powell, R.B. (2013) What leads to better visitor outcomes in live interpretation? Journal of Interpretation Research, 18(2), 9-44. DOI: 10.1177/109258721301800202
27) Powell, R.B. & Stern, M.J. (2013) Is it the program or the interpreter? Modeling the influence of program characteristics and interpreter attributes on visitor outcomes. Journal of Interpretation Research, 18(2), 45-60. DOI: 10.1177/109258721301800203
26) Powell, R.B. & Stern, M.J. (2013) Speculating on the role of context in the outcomes of interpretive programs. Journal of Interpretation Research, 18(2), 61-78. DOI: 10.1177/109258721301800204
25) Stern, M.J., Powell, R.B., McLean, K.D.*, Martin, E.*, Thomsen, J.M.* & Mutchler, B.A.* (2013) The difference between good enough and great: Bringing interpretive best practices to life. Journal of Interpretation Research, 18(2), 79-100. DOI: 10.1177/109258721301800205
24) Skibins, J.C.,* & Powell, R.B. (2013) Conservation Caring: Measuring the influence of zoo visitors' connection to wildlife on pro-conservation behaviors. Zoo Biology, 32(5), 528-540. DOI:10.1002/zoo.21086
23) Brownlee, M. T. J.*, Hallo, J. C., Wright, B. A., Moore, D., & Powell, R. B. (2013). Visiting a climate-influenced National Park: The stability of climate change perceptions. Environmental Management, 52(5), 1132-1148. DOI:10.1007/s00267-013-0153-2
22) Holladay, P.J.* & Powell, R.B. (2013) Resident perceptions of social-ecological resilience and the sustainability of community-based tourism development in the Commonwealth of Dominica. Journal of Sustainable Tourism, 21(8), 1188-1211.
21) Skibins, J.C.*, Powell, R.B. & Hallo, J.C. (2013) Charisma and conservation: Charismatic megafauna's influence on safari and zoo tourists' pro-conservation behaviors. Biodiversity and Conservation, 22(4), 959-982.
20) Brownlee, M.T.J.*, Powell, R. B., & Hallo, J. (2013) A review of the foundational processes that influence beliefs in climate change: Opportunities for environmental education research. Environmental Education Research, 19(1), 1-20. DOI:10.1080/13504622.2012.683389
19) Skibins, J.C.*, Powell, R.B., & Stern, M.J. (2012) Exploring empirical support for interpretation's best practices. Journal of Interpretation Research, 17(1), 25-44.
18) Vagias, W.M.*, Powell, R.B, Moore, D, & Wright, B.A. (2012) Development, psychometric qualities, and cross-validation of the Leave No Trace attitudinal inventory and measure (LNT AIM). Journal of Leisure Research, 44(2), 234-256. DOI:10.1080/00222216.2012.11950263
17) Van Riper, C., Powell, R. B., Machlis, G., Wagtendonk, J., van Riper, C.J.*,von Ruschkowski, E., Schwarzbach, S. & Galipeau, R. (2012) Using integrated research and interdisciplinary science: Potential benefits to managers of park and protected areas. George Wright Society Forum, 29(2), 216-226.
16) Stern, M.J., Wright, M.E.*, & Powell, R.B. (2012) Motivating school participation in National Park Service education programs. Journal of Visitor Studies, 15(1), 28-47.
15) Powell, R.B., Brownlee, M.T.J.*, Kellert, S. R. & Ham, S.H. (2012) From awe to satisfaction: Immediate affective responses to the Antarctic tourism experience. Polar Record, 48(2), 145-156.
14) Stern, M.J., Powell, R.B. & Hockett, K.S. (2011) Why do they come? Motivations and barriers to interpretive program attendance at Great Smoky Mountains National Park. Journal of Interpretation Research, 16(2), 35-52.
13) Baldwin, R.F., Powell, R.B., & Kellert, S.R. (2011) Habitat as architecture for sustainability: Integrating conservation planning and human health. Ambio, 40(3), 322-327.
12) Powell, R.B., Stern, M.J., Krohn, B.* & Ardoin, N. (2011) Development and validation of scales to measure environmental responsibility, attitudes toward school, and character development. Environmental Education Research, 17(1), 91-111. DOI:10.1080/13504621003692891
11) Stern, M.J., Powell, R.B., & Ardoin, N.M. (2011) Evaluating a constructivist and culturally responsive approach to environmental education for diverse audiences. Journal of Environmental Education, 42(2),109-122.
10) Stern, M.J., Powell, R.B., & Cook, C. (2010-2011) The benefits of live interpretive programs to Great Smoky Mountains National Park. Park Science, 27(3), 56-60.
9) Vagias, W.* & Powell, R.B. (2010) Backcountry visitors' Leave No Trace attitudes. International Journal of Wilderness, 16(3), 21-27.
8) Powell, R. B. (2010) Developing institutions to overcome governance barriers to ecoregional conservation. In S.C. Trombulak & R.F. Baldwin (Eds.), Landscape-scale Conservation Planning (pp. 53-67). New York: Springer.
7) Powell, R. B & Vagias, W.* (2010) Benefits of stakeholder involvement in the development of social science research. Park Science, 27(1), 46-49.
6) Powell, R.B., Cushnir, A., & Peiris, P. (2009) Overcoming governance barriers to integrated coastal zone, marine protected area, and sustainable tourism management in Sri Lanka. Coastal Management, 37(6), 633-655.
5) Powell, R.B., Kellert, S. R., & Ham, S.H. (2009) Interactional theory and the sustainable nature-based tourism experience. Society and Natural Resources, 22(8), 761-776.
4) Stern, M.J., Powell, R.B., & Ardoin, N. (2008) What difference does it make? Assessing student outcomes of participation in a residential environmental education program. Journal of Environmental Education, 39(4), 31-43.
3) Powell, R.B. & Ham, S.H. (2008) Can ecotourism interpretation really lead to pro-conservation knowledge, attitudes, and behavior? Evidence from the Galapagos Islands. Journal of Sustainable Tourism, 16(4), 467-489. DOI:10.1080/09669580802154223
2) Powell, R.B., Kellert, S. R., & Ham, S.H. (2008) Antarctic tourists: Ambassadors or consumers? Polar Record, 44(230), 233-241.
1) Powell, R.B., Stern, M.J., & Ardoin, N. (2006) A sustainable evaluation framework and its application. Applied Environmental Education and Communication, 5(4), 231-241.
*Graduate Student
2022 Outstanding Contributions to Research in Environmental Education Award. North American Association for Environmental Education.
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2016 Clemson University. College of Health, Education, and Human Development. Excellence in Research
2014 Calhoun Honors College and Pearce Center. Clemson University. Thoughts Worth Thinking Speaker
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text:
Open Journal of Endocrine and Metabolic Diseases
10.4236/ojemd.2017.73010
Is There Any Threshold for Vitamin D That Elevates Parathyroid Hormone
Meral Mert1, Gonca Tamer2, Nahide Ekici Gunay3, Ilkay Kartal2, Hamide Piskinpasa1*, Pinar Karakaya1, Yildiz Okuturlar4
1Clinic of Endocrinology and Metabolism, Bakirkoy Dr. Sadi Konuk Education and Research Hospital, Istanbul, Turkey
2Clinic of Endocrinology and Metabolism, Istanbul Medeniyet University Goztepe Education and Research Hospital, Istanbul, Turkey
3Central Laboratory, Kayseri Education and Research Hospital, Kayseri, Turkey
4Clinic of Internal Medicine, Bakirkoy Dr. Sadi Konuk Education and Research Hospital, Istanbul, Turkey
Received: March 1, 2017; Accepted: March 27, 2017; Published: March 30, 2017
Objective: To evaluate vitamin D status in relation to serum levels for parathyroid hormone (PTH) and corrected calcium among endocrine outpatients. Methods: A total of 760 patients (mean(SD) age: 40.0(12.6) years, 94.6% were females) admitted to our endocrinology outpatient clinic were included and evaluated with respect to patient demographics, serum levels for 25-hydrox- yvitamin D (25(OH) D, ng/mL), PTH (pg/mL) and corrected calcium (mg/dL) as well as the vitamin D status. Results: Vitamin D deficiency was determined in 65.0% and elevated PTH levels in 20.3% of patients. iPTH levels were significantly higher in females than in males (58.9(40.4) vs. 45.1(26.2) pg/mL, p = 0.031) and in summer than in winter cases (63.9(47.7) vs. 54.2(32.8) pg/mL, p = 0.002), whereas no difference was found in serum levels for 25(OH) D, corrected calcium and phosphate with respect to gender and season. Significantly higher levels for iPTH were noted in vitamin D deficient patients (60.7(43.9) pg/mL) than in normal (51.1(33.4) pg/mL) and vitamin D insufficient (57.1(26.0) pg/mL) cases (p = 0.03). iPTH levels were correlated positively with age (r = 0.116, p = 0.001) and negatively with corrected calcium (r = −0.097, p = 0.008), P (r = −0.224, p = 0.000) and 25(OH) D (r = −0.134, p = 0.000), whereas no correlation was noted between 25(OH) D and corrected calcium levels. Conclusion: Our findings indicated that vitamin D deficiency in 65.0%, whereas PTH elevation only in 20.3% of endocrine outpatients, despite the significantly negative correlation of PTH to 25(OH) D and significantly higher levels of PTH among vitamin D deficient cases than in vitamin D insufficient and sufficient cases. Gender's and seasonal differences had influence on serum levels for PTH but not on either 25(OH) D or corrected calcium, and no correlation was evident between 25(OH) D and corrected calcium levels.
Vitamin D Deficiency, Parathyroid Hormone, Calcium, 25(OH) D Testing
Vitamin D is an essential fat-soluble vitamin that affects nearly every organ system, and thereby, vitamin D deficiency has been associated not only with bone diseases such as rickets, osteoporosis and osteomalacia, but also with the risk of metabolic syndrome, diabetes, autoimmune diseases, cardiovascular disease, chronic kidney disease and certain types of cancers [1] - [8] .
Owing to greater awareness within the medical community regarding the importance of poor vitamin D status as a public health problem affecting almost every second person worldwide [2] [9] [10] [11] , the interest in the biology of vitamin D and vitamin D deficiency and thereby the demand for vitamin D testing has increased dramatically in the last 2 decades [12] [13] [14] .
The serum level of 25-hydroxyvitamin D (25(OH) D) is considered to be a reliable indicator of the vitamin D status of an individual [15] , and albeit there is no consensus on a cut-off level of vitamin D for defining vitamin D status categories, it has been widely accepted that circulating 25(OH) D concentrations of <30 ng/mL to indicate vitamin D insufficiency and levels < 20 ng/mL to be indicative of vitamin D deficiency [16] . Accordingly, it has been estimated that 40% to 100% of elderly US and European non-hospitalized men and women and an estimated one billion people worldwide, to be either vitamin D deficient or insufficient [2] [17] .
The plasma (or serum) 25(OH) D is currently the best indicator for vitamin D status as a measure of the circulating concentration of serum 25(OH) D, which reflects vitamin D from all sources including cutaneous synthesis, diet and supplements [2] [18] . However, given that it requires advanced technical equipment, not all investigators may have the resources to assay 25(OH) D and thus the clinical decision on vitamin D deficiency has been based on evaluation of serum levels for calcium, phosphate and parathyroid hormone (PTH) [19] . Therefore, the present study was designed to evaluate vitamin D status in relation to serum levels for PTH and corrected calcium among endocrine outpatients.
2.1. Study Population
A total of 760 patients (mean age: 40.0 (standard deviation (SD) =12.6; range: 15.0 - 86.0) years, 94.6% were females) admitted to Clinic of Endocrinology at Kayseri Training and Research Hospital were included in this study. Patients with exposure to sunlight for more than 30 minutes during summer months (Mar-Sep) and less than 30 minutes during winter months (Sep-Mar) were included, while patients with renal dysfunction, hyper- or hypo-parathyroidism or malabsorption and patients under calcium replacement therapy were excluded from the study.
Written informed consent was obtained from each subject following a detailed explanation of the objectives and protocol of the study which was conducted in accordance with the ethical principles stated in the "Declaration of Helsinki" and approved by the institutional ethics committee.
Data on patient demographics, serum levels for 25(OH) D (ng/mL), PTH (pg/mL) and corrected calcium (mg/dL) were recorded. Vitamin D status of patients were categorized according to the published criteria based on serum levels for 25(OH) D as adequate vitamin D (≥30 ng/ml), vitamin D insufficiency (20 - 29 ng/ml) and vitamin D deficiency (<20 ng/ml) [20] .
Seasonal variation in 25(OH) D (ng/mL), PTH (pg/mL) and corrected calcium (mg/dL) levels, the alteration in PTH (pg/mL) and corrected calcium (mg/dL) levels with respect to vitamin D status and the correlation between 25(OH) D (ng/mL), PTH (pg/mL) and corrected calcium (mg/dL) levels were determined in both genders.
2.3. Blood Biochemistry
Patient's venous serum and plasma specimens with addition of the ethylenediaminetetraacetic acid (EDTA) to be used in biochemistry and hormone analyzes are taken between 0.8 - 0.10 in the morning after 12 hours fasting. All laboratory test parameters, except iPTH, were measured within 3 hours. iPTH plasma samples stored −80˚C until final analysis.
Insulin and iPTH levels were measured in an autoanalyzer (Beckman Coulter Unicel DXI 800, Brea, California, USA) with original commercial original kit, controls and calibrators of the same lot number; using the the paramagnetic particle and chemiluminescence immunoanalysis method for the quantitative determination. For insulin analysis, the total correlation coefficient (CV) was detected as 5.6% at 0.15 μIU/mL concentrations, 4.0% at 0.30 μIU/mL concentrations, 4.5% at 0.93 μIU/mL concentrations, 3.5% at 12.90 μIU/ml concentrations, 3.3% at 37.40 μIU/mL concentration and 3.1% at 99.30 μIU/mL concentrations. In human plasma samples coefficients of variation for iPTH test was detected to be 2.6% within the study at 12.1 (1.3) pg/ml (pmol/L) concentration, 5.8% between the study, 1.6% within the study at 144 (15.3) pg/ml (pmol/L) concentration, 3.2% between the study, 2.2% within the study at 1439 (152.5) pg/ml (pmol/L) and 2.8% between the study.
Serum intact PTH was measured from venous blood samples using a solid-phase two-site chemiluminescent enzyme-labeled immunometric assay with a reference range of 12 - 88 pg/mL.
Plasma levels of vitamin D of patient cohorts were measured at the Depart- ment of Clinical Biochemistry of Kayseri Education and Research Hospital CentralLaboratory. Samples were analyzed by a high-performance liquid chromatograph (HPLC) method using the Immuchrom HPLC system (Immuchrom GmbH, Heppenheim, Germany) and Immuchrom vitamin D3 controls and kit (Immuchrom GmbH, Heppenheim, Germany).
500 μL plasma sample from EDTA was purified from proteins and 50 μL of the cleaned supernatant was applied into instrument. The flow rate of the methanol water mixture used as the mobile phase was 1.1 mL/minute. An UV detector was used during the analysis. Vitamin D levels were detected as 2.6% at 56.5 nmol/L concentration and 1.5% at 104.8 nmol/L concentration. Inter-assay values were measured as 4.0% at 54.1 nmol concentration and 3.6% at 105.4 nmol concentration [1] .
Serum calcium, phosphorus were measured colorimetrically. Serum albumin levels were measured by immunoturbidimetric assay. Corrected calcium (adjust- ed calcium) levels were determined via using formulae "corrected calcium (mg/dL) = measured total calcium (mg/dL) + 0.8 (4.0 - serum albumin [g/dL])", where 4.0 represents the average albumin level in g/dL.
Statistical analysis was made using computer software (SPSS version 16.0, SPSS Inc. Chicago, IL, USA). Chi-square test for the comparison of categorical data and student-t-test was used for the analysis of numerical data. The relation between 25OH (D), corrected calcium and PTH was evaluated with Pearson correlation analysis. Data were expressed as "mean (SD)", and percent (%) where appropriate. p < 0.05 was considered statistically significant.
3.1. Patient Characteristics and Laboratory Findings
Vitamin D levels were normal in 20.4% of patients, while 14.6% and 65.0% of patients were determined to be vitamin D insufficient and deficient, respectively. PTH levels were determined to be elevated in 20.3% of patients, similarly in winter (19.9%) and summer (20.8%) months (Table 1). Age and biochemical variables with respect to gender can be seen in Table 2. Mean age of males vs females (46.1(15.4) vs. 39.7(12.4) years, p = 0.013) was found. Moreover, mean ages of summer cases vs winter cases(43.8(13.4) vs. 37.4(11.4) years, p = 0.0001) were significantly older. iPTH levels were significantly higher in females than in males (58.9(40.4) vs. 45.1(26.2) pg/mL, p = 0.031) and in summer than in winter cases (63.9(47.7) vs. 54.2(32.8) pg/mL, p = 0.002), particularly for females (p = 0.001). Calcium levels were significantly higher in summer compared with winter cases (9.6(1.8) vs. 9.4(0.5) mg/dL, p = 0.048), particularly for females (p = 0.048). No difference was noted in serum levels for 25(OH) D, corrected calcium and phosphate with respect to gender and season (Table 2).
3.2. Age, Biochemical Variables and Seasonal Distribution with Respect to Vitamin D Status
Significantly higher levels for iPTH were noted in vitamin D deficient patients
Table 1. Patient characteristics and categories with respect to season, vitamin D status and PTH level.
Table 2. Age and biochemical variables with respect to gender and season.
Data are shown as mean (SD). Ca: calcium; PTH: parathyroid hormone; 25(OH) D: 25-hydroxyvitamin D.
Table 3. Age, biochemical variables and seasonal distribution with respect to vitamin D status.
Ca: calcium; PTH: parathyroid hormone; 25(OH) D: 25-hydroxyvitamin D.
Table 4. Correlation between biochemical variables.
Ca: calcium; PTH: parathyroid hormone; 25(OH) D: 25-hydroxyvitamin D; Pearson correlation analysis. Correlation is significant at 0.05 level (2-tailed).
(60.7(43.9) pg/mL) than in normal (51.1(33.4) pg/mL) and vitamin D insufficient (57.1(26.0) pg/mL) cases (p = 0.03), whereas no difference was noted in vitamin D status with respect to age, corrected calcium levels, and seasonal change (Table 3).
3.3. Correlation between Biochemical Variables
iPTH levels were correlated positively with age (r = 0.116, p = 0.001) and negatively with corrected calcium (r = −0.097, p = 0.008), P (r = −0.224, p = 0.000) and 25(OH) D (r = −0.134, p = 0.000), whereas no correlation was noted between 25(OH) D and corrected calcium levels (Table 4).
Our findings in a cohort of endocrine outpatients indicated that vitamin D deficiency was clearly prevalent as noted in 65.0% of patients with no alteration in vitamin D status, 25(OH) D levels and corrected calcium levels with respect to gender and season. Increased levels for PTH were noted in females than in males and in vitamin D deficient than in normal and vitamin D insufficient patients. Negative correlation of PTH levels both to 25(OH) D and corrected calcium was noted, while no correlation was evident between 25(OH) D and corrected calcium levels.
High prevalence of vitamin D deficiency in our study population is in agreement with the consistently reported high prevalence of vitamin D deficiency in different populations worldwide even in areas that receive ample sunlight [14] [21] [22] [23] [24] . Also, evaluation of vitamin D status via a population-based survey of households in the Aegean region of Turkey indicated that 74.9% of the subjects had 25(OH) D deficiency (<20 ng/mL) [25] .
In a retrospective study to analyze the biochemical results stored in the database of a pathology laboratory, it was reported that 33% of 3745 men and 40% of 6754 women were vitamin D deficient to some degree (25[OH] D ≤ 50 nmol/L) along with a significant negative association between PTH and 25(OH) D, while a significant positive association between calcium and 25(OH) D levels [12] . Supporting data from past studies, PTH levels were higher in vitamin D deficient than in vitamin D insufficient patients along with a negative correlation between 25(OH) D and PTH in the present study [12] [17] [26] [27] [28] .
However, despite 65.0% prevalence of vitamin D deficiency and the negative correlation between 25(OH) D and PTH levels, PTH levels were within normal range in majority of our patients with identification of elevated PTH levels only in 20.3%. Alike to our findings, data from ambulatory patients of an outpatient clinic in Poland revealed 84.4% of subjects to be vitamin D deficient (25(OH) D < 20 ng/mL), while 21% of subjects had elevated serum PTH concentration (i.e. >62 pg/mL) along with a negative correlation between PTH and 25(OH) D concentrations [26] .
Indeed, data from some studies indicated an association between vitamin D deficiency and elevated PTH levels [12] [29] [30] [31] [32] leading consideration of the theoretical plateau in PTH as 25(OH) D increases to be used as a determinant in establishing the adequacy of vitamin D status [33] . However it should be noted that while 25(OH) D and PTH levels are inversely related, less than half of the patients with a low vitamin D level have been confirmed to have an elevated PTH, and, in most of these patients, the PTH does not immediately normalize with correction of the vitamin D [27] [34] . Likewise, blunted parathyroid hormone response to vitamin D deficiency was reported in a past study conducted with premenopausal women along with no difference between serum PTH levels of the subjects with and without vitamin D deficiency [35] . Hence, our findings support that PTH has a limited role in defining vitamin D status in individual patients and in guiding vitamin D therapy in clinical practice [34] .
In contrast to data from past studies indicated that season of blood withdrawal was a significant predictor of vitamin D status, with identification of lower median 25(OH) D levels during winter and spring [36] [37] [38] , seasonal alteration had no influence on 25(OH) D levels as well as corrected calcium levels in our study population, whereas serum PTH levels were higher in summer cases, especially among females. Lack of the effect of seasonal difference on serum vitamin D levels was also reported in a past study in stroke patients which revealed similar levels for vitamin D levels between the cases in summer (Apr-Sep) and winter (Oct-Mar) [39] .
While no data are available to indicate whether seasonal variation in 25(OH) D is good, bad or neutral for health, vitamin D deficiency (<30 nmol/L) in summer has been of concern, as this implies a much lower level is likely in winter, and should certainly prompt treatment and checking of the winter level [40] . In this regard, our findings may emphasize the insufficient exposure to sunlight even in summer months during which sun exposure is more effective in promoting vitamin D activation as well as its storage for an optimal vitamin D status during the remaining months of the year [36] .
Higher levels of PTH in summer than in winter months among females in the present study is contradictory to the higher winter-time than summer-time prevalence of secondary hyperparathyroidism shown in past studies [12] [41] [42] . Given that absence of seasonal variation of 25(OH) D levels in our cohort, our findings seem to emphasize the influence of confounding variables, such as weight status, calcium intake and calcium absorption on elevation in PTH levels [17] [27] [36] [43] .
Likewise, lack of a gender influence on 25(OH) D levels in the present cohort seems also contradictory to previous reports indicated that females had significantly lower mean 25(OH) D levels and thereby were more likely to be vitamin D deficient than men [12] [25] [44] [45] [46] [47] . Indeed, likely to be influenced by the cultural attitudes towards sun exposure and concealing clothes [48] [49] , the role of gender in the determination of vitamin D status has not yet been clarified and lack of a gender influence on vitamin D status was also reported in other studies [36] [50] [51] [52] .
In a retrospective study to analyze the biochemical results stored in the database of a pathology laboratory, it was reported that 33% of 3745 men and 40% of 6754 women were vitamin D deficient to some degree (25[OH] D ≤ 50 nmol/L) along with a significant negative association between PTH and 25(OH) D and a significant positive association between calcium and 25(OH) D levels [12] .
PTH levels but not corrected calcium levels were correlated with 25(OH) D in the present study, whereas it should be noted that, while not correlated directly with 25(OH) D levels, corrected Ca levels were negatively correlated with PTH levels and in contrast to Ca levels, this relationship was free from the season effect.
Although, serum 25(OH) D levels have been widely accepted as the best indicator of a person's short-term vitamin D status not all investigators have the resources to assay 25(OH) D [53] .
In this regard, given the increased demand for 25(OH) D testing in the clinical practice [12] as the fastest growing Medicare item that increased exponentially over the past 15 years [40] , our findings indicate that PTH levels rather than corrected Ca levels more accurately reflect vitamin D status in case of unavailability of 25(OH) D testing, provided that gender and seasonal variations are considered. Nevertheless, it should be kept in mind that, given the discrepancy between the rates of vitamin D deficiency and elevated PHT within a study population, PTH has been considered to have a limited role in either defining vitamin D status in individual patients or guiding vitamin D therapy in clinical practice [34] .
Although, the potential benefits of improving a population's vitamin D status would be substantial given the high burden of vitamin D deficiency, lack of clear evidence-based guidelines regarding the long-term management of incidentally detected cases as well as differentiating clinically significant cases from an incidental biochemical finding have been considered to be the major clinical challenges [54] . Given the growing interest and demand for 25(OH) D testing, further investigation on identification of subpopulations that are mostly affected by vitamin D deficiency seems to be helpful in more appropriate and targeted allocation of scarce healthcare resources and services [12] .
Certain limitations to this study should be considered. No data are available on body mass index, physical activity and diet characteristics in the study population despite their well-known effect on serum 25(OH) D levels. Also, while likely to contribute to the changes in the serum PTH responses to changes in serum 25(OH) D levels, no data are available considering the weight status as well as dietary calcium intake in our patients. Accordingly, lack of data on these confounding factors seems to be the major limitation which otherwise would extend the knowledge achieved in the current study. Nevertheless, despite these certain limitations, given the paucity of the solid information available on this area, our findings represent a valuable contribution to the literature.
The relationship between the serum levels of 25(OH) D and maximal suppression of PTH has been assessed in a few studies. Results from one investigation show that serum 25(OH) D needs to be higher than 31 ng/mL to suppress PTH in normal weight adult populations [55] . Lotito, et al. found that, lower doses of vitamin D along with calcium can also significantly suppress PTH in the meta-analysis [56] .
In conclusion, our findings indicated that vitamin D deficiency in 65.0%, whereas PTH elevation only in 20.3% of endocrine outpatients, despite the significant negative correlation of PTH to 25(OH) D and significantly higher levels of PTH among vitamin D deficient cases than in vitamin D insufficient and sufficient cases. Gender and seasonal difference had influence on serum levels for PTH but not on either 25(OH) D or corrected calcium, and no correlation was evident between 25(OH) D and corrected calcium levels. Accordingly, while our findings support that 25(OH) D testing is the best indicator of a person's vitamin D status, given that not all investigators have the resources to assay 25(OH) D, PTH levels rather than corrected calcium levels may more accurately reflect vitamin D status with consideration of gender and seasonal variations.
There is no conflict of interest for all authors.
This article does not contain any studies animals performed by any of the authors.
Mert, M., Tamer, G., Gunay, N.E., Kartal, I., Piskinpasa, H., Karakaya, P. and Okuturlar, Y. (2017) Is There Any Threshold for Vitamin D That Elevates Parathyroid Hormone. Open Journal of Endocrine and Metabolic Diseases, 7, 97-110. https://doi.org/10.4236/ojemd.2017.73010
1. Holick, M.F. (2003) Evolution and Function of Vitamin D. Recent Results Cancer Research, 164, 3-28.
2. Holick, M.F. (2007) Vitamin D Deficiency. New England Journal of Medicine, 357, 266-281.
https://doi.org/10.1056/NEJMra070553
3. Chambers, E.S. and Hawrylowicz, C.M. (2011) The Impact of Vitamin D on Regulatory T Cells. Current Allergy and Asthma Reports, 11, 29-36.
4. Hypponen, E., Laara, E., Reunanen, A., Jarvelin, M.R. and Virtanen, S.M. (2001) Intake of Vitamin D and Risk of Type 1 Diabetes: A Birthcohort Study. Lancet, 358, 1500-1503.
5. Kendrick, J., Targher, G., Smits, G. and Chonchol, M. (2009) 25-Hydroxyvitamin D Deficiency is Independently Associated with Cardiovascular Disease in the Third National Health and Nutrition Examination Survey. Atherosclerosis, 205, 255-260.
https://doi.org/10.1016/j.atherosclerosis.2008.10.033
6. Williams, S., Malatesta, K. and Norris, K. (2009) Vitamin D and Chronic Kidney Disease. Ethnicity & Disease, 19, 5-11.
7. Penckofer, S., Kouba, J., Wallis, D.E. and Emanuele, M.A. (2008) Vitamin D and Diabetes: Let the Sunshine in. The Diabetes Educator, 34, 939-940.
8. Jenab, M, Bueno-de-Mesquita, H.B., Ferrari, P., et al. (2010) Association between Pre-Diagnostic Circulating Vitamin D Concentration and Risk of Colorectal Cancer in European Populations: A Nested Case-Control Study. The British Medical Journal, 340b, 5500.
https://doi.org/10.1136/bmj.b5500
9. Pilz, S., Tomaschitz, A., Drechsler, C., Zittermann, A., Dekker, J.M. and Marz, W. (2011) Vitamin D Supplementation: A Promising Approach for the Prevention and Treatment of Strokes. Current Drug Targets, 12, 88-96.
10. Lee, J.H., O'Keefe, J.H. and Bell, D. (2008) Vitamin D Deficiency: An Important, Common, and Easily Treatable Cardiovascular Risk Factor? American College of Cardiology, 52, 1949-1956.
https://doi.org/10.1016/j.jacc.2008.08.050
11. Wagner, C.L. and Greer, F.R. (2008) Prevention of Rickets and Vitamin D Deficiency in Infants, Children, and Adolescents. Pediatrics, 122, 1142-1152.
12. Quaggiotto, P., Tran, H. and Bhanugopan, M. (2014) Vitamin D Deficiency Remains Prevalent Despite Increased Laboratory Testing in New South Wales, Australia. Singapore Medical Journal, 55, 271-280.
https://doi.org/10.11622/smedj.2014071
13. Krasowski, M.D. (2011) Pathology Consultation on Vitamin D Testing. American Journal of Clinical Pathology, 136, 507-514.
https://doi.org/10.1309/AJCPB50USETUOQDZ
14. Gronli, O., Kvamme, J.M., Jorde, R. and Wynn, R. (2014) Vitamin D Deficiency Is Common in Psychogeriatric Patients, Independent of Diagnosis. BMC Psychiatry 8, 14, 134.
https://doi.org/10.1186/1471-244x-14-134
15. Lips, P. (2004) Which Circulating Level of 25-Hydroxyvitamin D Is Appropriate? The Journal of Steroid Biochemistry and Molecular Biology, 89-90, 611-614.
https://doi.org/10.1016/j.jsbmb.2004.03.040
16. Chapuy, M.C., Preziosi, P., Maamer, M., Arnaud, S., Galan, P., et al. (1997) Prevalence of Vitamin D Insufficiency in an Adult Normal Population. Osteoporosis International, 7, 439-443.
https://doi.org/10.1007/s001980050030
17. Lu, H.K., Zhang, Z., Ke, Y.H., He, J.W., Fu, W.Z., Zhang, C.Q. and Zhang, Z.L. (2012) High Prevalence of Vitamin D Insufficiency in China: Relationship with the Levels of Parathyroid Hormone and Markers of Bone Turnover. Plos One, 7, e47264.
18. Lips, P. (2001) Vitamin D Deficiency and Secondary Hyperparathyroidism in the Elderly: Consequences for Bone Loss and Fractures and Therapeutic Implications. Endocrine Reviews, 22, 477-501.
https://doi.org/10.1210/edrv.22.4.0437
19. Holick, M.F. (2006) High Prevalance of Vitamin D Inadequacy and Implications for Health. Mayo Clinic Proceedings, 81, 353-373.
https://doi.org/10.4065/81.3.353
20. Watts, N.B., Bilezikian, J.P., Camacho, P.M., Greenspan, S.L., Harris, S.T., Hodgson, S.F., Kleerekoper, M., Luckey, M.M., McClung, M.R., Pollack, R.P. and Petak, S.M. (2010) AACE Osteoporosis Task Force. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Diagnosis and Treatment of Postmenopausal Osteoporosis. Endocrine Practice Official Journal of the American College of Endocrinology & the American Association of Clinical Endocrinologists, 16, 1-37.
https://doi.org/10.4158/EP.16.S3.1
21. French, D., Gorgi, A.W., Ihenetu, K.U., et al. (2011) Vitamin D Status of County Hospital Patients Assessed by the DiaSorin LIAISON® 25-Hydroxyvitamin D Assay. Clinica Chimica Acta, 412, 258-262.
https://doi.org/10.1016/j.cca.2010.10.013
22. Kuriacose, R. and Olive, K.E. (2008) Prevalence of Vitamin D Deficiency and Insufficiency in Northeast Tennessee. Southern Medical Journal, 101, 906-909.
https://doi.org/10.1097/SMJ.0b013e318181881b
23. Anderson, J.L., May, H.T., Horne, B.D., et al. (2010) Relation of Vitamin D Deficiency to Cardiovascular Risk Factors, Disease Status, and Incident Events in a General Healthcare Population. American Journal of Cardiology, 106, 963-968.
24. Bang, U.C., Semb, S., Nordgaard-Lassen, I. and Jensen, J.E. (2009) A Descriptive Crosssectional Study of the Prevalence of 25-Hydroxyvitamin D Deficiency and Association with Bone Markers in a Hospitalized Population. Nutrition Research, 29, 671-675.
https://doi.org/10.1016/j.nutres.2009.09.010
25. Hekimsoy, Z., Dinc, G., Kafesciler, S., Onur, E., Güvenc, Y., Pala, T., Güclü, F. and Ozmen, B. (2010) Vitamin D Status among Adults in the Aegean Region of Turkey. BMC Public Health, 10, 782.
26. Kmiec, P., Zmijewski, M., Waszak, P., Sworczak, K. and Lizakowska-Kmiec, M. (2014) Vitamin D Deficiency during Winter Months among an Adult, Predominantly Urban, Population in Northern Poland. Endokrynologia Polska, 65, 105-113.
https://doi.org/10.5603/EP.2014.0015
27. Chung, I.H., Kim, H.J., Chung, S. and Yoo, E.G. (2014) Vitamin D Deficiency in Korean Children: Prevalence, Risk Factors, and the Relationship with Parathyroid Hormone Levels. Annals of Pediatric Endocrinology & Metabolism, 19, 86-90.
https://doi.org/10.6065/apem.2014.19.2.86
28. Tamer, G., Arik, S., Tamer, I. and Coksert, D. (2011) Relative Vitamin D Insufficiency in Hashimoto's Thyroiditis. Thyroid, 21, 891-896.
https://doi.org/10.1089/thy.2009.0200
29. Houghton, L.A., Szymlek-Gay, E.A., Gray, A.R., et al. (2010) Predictors of Vitamin D Status and Its Association with Parathyroid Hormone in Young New Zealand Children. American Journal of Clinical Nutrition, 92, 69-76.
https://doi.org/10.3945/ajcn.2009.29055
30. Schoenmakers, I., Ginty, F., Jarjou, L.M., et al. (2010) Interrelation of Parathyroid Hormone and Vitamin D Metabolites in Adolescents from the UK and the Gambia. Journal of Steroid Biochemistry & Molecular Biology, 121, 217-220.
31. Napiórkowska, L., Budlewski, T., Jakubas-Kwiatkowska, W., et al. (2009) Prevalence of Low Serum Vitamin D Concentration in an Urban Population of Elderly Women in Poland. Polskie Archiwum Medycyny Wewntrznej, 119, 699-703.
32. Hochwald, O., Harman-Boehm, I. and Castel, H. (2004) Hypovitaminosis D among Inpatients in a Sunny Country. Israel Medical Association Journal IMAJ, 6, 82-87.
33. Muscogiuri, G., Mitri, J., Mathieu, C., Badenhoop, K., Tamer, G., Orio, F., Mezza, T., Vieth, R., Colao, A. and Pittas, A. (2014) Mechanisms in Endocrinology: Vitamin D as a Potential Contributor in Endocrine Health and Disease. European Journal of Endocrinology, 171, 101-110.
34. Shibli-Rahhal, A. and Paturi, B. (2014) Variations in Parathyroid Hormone Concentration in Patients with Low 25 Hydroxyvitamin D. Osteoporosis International, 25, 1931-1936.
35. Tamer, G., Mesci, B., Tamer, I., Kilic, D. and Arik, S. (2012) Is Vitamin D Deficiency an Independent Risk Factor for Obesity and Abdominal Obesity in Women? Endokrynologia Polska, 63, 196-201.
36. Vierucci, F., Del Pistoia, M., Fanos, M., Erba, P. and Saggese, G. (2014) Prevalence of Hypovitaminosis D and Predictors of Vitamin D Status in Italian Healthy Adolescents. Italian Journal of Pediatrics, 40, 54.
https://doi.org/10.1186/1824-7288-40-54
37. Dong, Y., Pollock, N., Stallmann-Jorgensen, I.S., Gutin, B., Lan, L., Chen, T.C., Keeton, D., Petty, K., Holick, M.F. and Zhu, H. (2010) Low 25-Hydroxyvitamin D Levels in Adolescents: Race, Season, Adiposity, Physical Activity, and Fitness. Pediatrics, 125, 1104-1111.
38. Kim, S.H., Oh, M.K., Namgung, R. and Park, M.J. (2014) Prevalence of 25-Hydroxyvitamin D Deficiency in Korean Adolescents: Association with Age, Season and Parental Vitamin D Status. Public Health Nutrition, 17, 122-130.
39. Gupta, A., Prabhakar, S., Modi, M., Bhadada, S.K., Lal, V. and Khurana, D. (2014) Vitamin D Status and Risk of Ischemic Stroke in North Indian Patients. Indian Journal of Endocrinology & Metabolism, 18, 721-725.
40. Lucas, R. and Neale, R. (2014) What Is the Optimal Level of Vitamin D?-Separating the Evidence from the Rhetoric. Australian Family Physician, 43, 119-122.
41. Heaney, R.P. (2008) Vitamin D: Criteria for Safety and Efficacy. Nutrition Reviews, 66, S178-S181.
42. Grant, W.B., Cross, H.S., Garland, C.F., et al. (2009) Estimated Benefit of Increased Vitamin D Status in Reducing the Economic Burden of Disease in Western Europe. Progress in Biophysics & Molecular Biology, 99,104-113.
https://doi.org/10.1016/j.pbiomolbio.2009.02.003
43. Grethen, E., McClintock, R., Gupta, C.E., Jones, R., Cacucci, B.M. and Diaz, D., et al. (2011) Vitamin D and Hyperparathyroidism in Obesity. Journal of Clinical Endocrinology & Metabolism, 96, 1320-1326.
https://doi.org/10.1210/jc.2010-2202
44. Hirani, V., Tull, K., Ali, A. and Mindell, J. (2010) Urgent Action Needed to Improve Vitamin D Status among Older People in England! Age and Ageing, 39, 62-68.
https://doi.org/10.1093/ageing/afp195
45. Hypponen, E. and Power, C. (2007) Hypovitaminosis D in British Adults at Age 45 Y: Nationwide Cohort Study of Dietary and Lifestyle Predictors. American Journal of Clinical Nutrition, 85, 860-868.
46. Levis, S., Gomez, A., Jimenez, C., Veras, L., Ma, F., Lai, S., Hollis, B. and Roos, B.A. (2005) Vitamin D Deficiency and Seasonal Variation in an Adult South Florida Population. Journal of Clinical Endocrinology & Metabolism, 90, 1557-1562.
47. Atli, T., Gullu, S., Uysal, A.R. and Erdogan, G. (2005) The Prevalence of Vitamin D Deficiency and Effects of Ultraviolet Light on Vitamin D Levels in Elderly Turkish Population. Archives of Gerontology & Geriatrics, 40, 53-60.
https://doi.org/10.1016/j.archger.2004.05.006
48. Al-Musharaf, S., Al-Othman, A., Al-Daghri, N.M., Krishnaswamy, S., Yusuf, D.S., Alkharfy, K.M., Al-Saleh, Y., Al-Attas, O.S., Alokail, M.S., Moharram, O., Yakout, S., Sabico, S. and Chrousos, G.P. (2012) Vitamin D Deficiency and Calcium Intake in Reference to Increased Body Mass Index in Children and Adolescents. European Journal of Pediatrics, 171, 1081-1086.
49. Andiran, N., Celik, N., Akca, H. and Dogan, G. (2012) Vitamin D Deficiency in Children and Adolescents. Journal of Clinical Research in Pediatric Endocrinology, 4, 25-29.
https://doi.org/10.4274/jcrpe.574
50. Gordon, C.M., DePeter, K.C., Feldman, H.A., Grace, E. and Emans, S.J. (2004) Prevalence of Vitamin D Deficiency among Healthy Adolescents. Archives of Pediatrics & Adolescent Medicine, 158, 531-537.
https://doi.org/10.1001/archpedi.158.6.531
51. Marwaha, R.K., Tandon, N., Reddy, D.R., Aggarwal, R., Singh, R., Sawhney, R.C., Saluja, B., Ganie, M.A. and Singh, S. (2005) Vitamin D and Bone Mineral Density Status of Healthy Schoolchildren in Northern India. American Journal of Clinical Nutrition, 82, 477-482.
52. Weng, F.L., Shults, J., Leonard, M.B., Stallings, V.A. and Zemel, B.S. (2007) Risk Factors for Low Serum 25-Hydroxyvitamin D Concentrations in Otherwise Healthy Children and Adolescents. American Journal of Clinical Nutrition, 86, 150-158.
53. Millen, A.E. and Bodnar, L.M. (2008) Vitamin D Assessment in Population-Based Studies: A Review of the Issues. American Journal of Clinical Nutrition, 87, 1102-1105.
54. Chakraborty, S. and Mallath, M.K. (2014) Response to the Editorial on "Defining Vitamin D Deficiency, Using Surrogate Markers". Indian Journal of Endocrinology and Metabolism, 18, 246.
55. Gallagher, J.C., Yalamanchili, V. and Smith, L.M. (2012) The Effect of Vitamin D Supplementation on Serum 25OHD in Thin and Obese Women. Journal of Steroid Biochemistry & Molecular Biology, 136, 195-200.
56. Lotito, A., Teramoto, M., Cheung, M., Becker, K. and Sukumar, D. (2017) Serum Parathyroid Hormone Responses to Vitamin D Supplementation in Overweight/ Obese Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Nutrients, 9, 241.
https://doi.org/10.3390/nu9030241
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