***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: There is limited information on the effects of vitamin D on serum 25 hydroxyvitamin D ( 25OHD ) in young people and none on African Americans . The main objective of this trial was to measure the effect of different doses of vitamin D3 on serum 25OHD and serum parathyroid hormone ( PTH ) in young women with vitamin D insufficiency ( serum 25OHD ≤ 20 ng/mL ( 50 nmol/L ) . A r and omized double-blind placebo-controlled trial of vitamin D3 was conducted in young white and African American women , age 25 to 45 years . A total of 198 healthy white ( 60 % ) and African American ( 40 % ) women were r and omly assigned to placebo , or to 400 , 800 , 1600 , or 2400 IU of vitamin D3 daily . Calcium supplements were added to maintain a total calcium intake of 1000 to 1200 mg daily . The primary outcomes of the study were the final serum 25OHD and PTH levels at 12 months . The absolute increase in serum 25OHD with 400 , 800 , 1600 , and 2400 IU of vitamin D daily was slightly greater in African American women than in white women . On the highest dose of 2400 IU/d , the mixed model predicted that mean 25OHD increased from baseline 12.4 ng/mL ( 95 % confidence interval [ CI ] , 9.2 - 15.7 ) to 43.2 ng/mL ( 95 % CI , 38.2 - 48.1 ) in African American women and from 15.0 ng/mL ( 95 % CI , 12.3 - 17.6 ) to 39.1 ng/mL ( 95 % CI , 36.2 - 42.0 ) in white women . There was no significant effect  of vitamin D dose on serum PTH in either race but there was a significant inverse relationship between final serum PTH and serum 25OHD . Serum 25OHD exceeded 20 ng/mL in 97.5 % of whites on the 400 IU/d dose and between 800 and 1600 IU/d for African Americans . The recommended dietary allowance ( RDA ) suggested by the Institute of Medicine for young people is 600 IU daily . The increase in serum 25OHD  after vitamin D supplementation was similar in young and old , and in white and African American women OBJECTIVE In observational studies , low serum 25-hydroxyvitamin D [ 25(OH)D ] concentrations have been associated with insulin resistance and other risk factors for cardiovascular disease . RESEARCH DESIGN AND METHODS We present 1-year data from an ongoing 5-year trial in 511 individuals with impaired fasting glucose ( IFG ) and /or impaired glucose tolerance ( IGT ) r and omly assigned to 20,000 IU/week vitamin D3 or placebo .  An oral glucose tolerance test was performed at baseline and after 1 year . RESULTS Mean baseline serum 25(OH)D was 59.9 nmol/L and 61.1 nmol/L in the vitamin D and placebo groups , respectively , and increased by 45.8 nmol/L and 3.4 nmol/L , respectively . With adjustment for baseline concentrations , no differences in measures of glucose metabolism , insulin secretion or sensitivity , blood pressure , or hs-CRP were found after 1 year . There was a slight , but significant decrease in total and LDL cholesterol in the vitamin D group compared with the placebo group , but as there was also a decrease in HDL cholesterol , the change in the total/HDL cholesterol ratio did not differ significantly . Only analyzing subjects with 25(OH)D < 50 nmol/L did not change the results . CONCLUSIONS This study shows that vitamin D supplementation does not improve glycemic indices , blood pressure , or lipid status in subjects with IFG and /or IGT CONTEXT Observational studies show an association between low vitamin D status assessed by circulating 25-hydroxyvitamin D and cardiovascular events and mortality . Data from r and omized controlled trials are limited . OBJECTIVE The aim of this study was to test whether daily doses of vitamin D(3 ) at 400 or 1000 IU/d for 1 yr affected conventional markers of cardiovascular disease ( CVD ) risk . DESIGN We conducted a parallel-group , double-blind , placebo-controlled r and omized controlled trial . R and omization was computer generated . Participants and study investigators were blinded to intervention groupings throughout the trial . SETTING The study was conducted at the Clinical Research Facility , University of Aberdeen , United Kingdom . PARTICIPANTS A total of 305 healthy postmenopausal women aged 60 - 70 yr were recruited for the study . INTERVENTION Each woman received a daily capsule of 400 or 1000 IU vitamin D(3 ) or placebo r and omly allocated . MAIN OUTCOME MEASURES Primary outcomes were serum lipid profile [ total , high-density lipoprotein , and low-density lipoprotein cholesterol ; triglycerides ; and apolipoproteins A-1 and B100 ] , insulin resistance ( homeostatic model assessment ) , inflammatory biomarkers ( high-sensitivity C-reactive protein , IL-6 , soluble intracellular adhesion molecule-1 ) , and blood pressure . RESULTS A total of 265 ( 87 % ) participants completed all study visits . Small differences between groups for serum apolipoprotein B100 change [ repeated measures ANOVA , P=0.04 ; mean ( sd ) , -1.0 ( 10.0 ) mg/dl ( 400 IU ) ; -1.0 ( 10.0 ) mg/dl ( 1000 IU ) ; and + 0.02 ( 10.0 ) mg/dl ( placebo ) ] were not considered clinical ly significant . Other systemic markers for CVD risk remained unchanged . There was significant seasonal variation in systolic and diastolic blood pressure independent of vitamin D dose ( P<0.001 , linear mixed model ) . Mean ( sd ) reduction in systolic blood pressure from winter to summer was -6.6 ( 10.8 ) mm Hg . CONCLUSIONS Improving vitamin D status through dietary supplementation is unlikely to reduce CVD risk factors . Confounding of seasonality should be recognized and addressed in future studies of vitamin BACKGROUND Numerous observational studies have found supplemental calcium and vitamin D to be associated with reduced risk of common cancers . However , interventional studies to test this effect are lacking . OBJECTIVE The purpose of this analysis was to determine the efficacy of calcium alone and calcium plus vitamin D in reducing incident cancer risk  of all types . DESIGN This was a 4-y , population -based , double-blind , r and omized placebo-controlled trial . The primary outcome was fracture incidence , and the principal secondary outcome was cancer incidence . The subjects were 1179 community-dwelling women r and omly selected from the population of healthy postmenopausal women aged > 55 y in a 9-county rural area of Nebraska centered at latitude 41.4 degrees N. Subjects were r and omly assigned to receive 1400 - 1500 mg supplemental calcium/d alone ( Ca-only ) , supplemental calcium plus 1100 IU vitamin D3/d ( Ca + D ) , or placebo . RESULTS When analyzed by intention to treat , cancer incidence was lower in the Ca + D women than in the placebo control subjects ( P < 0.03 ) . With the use of logistic regression , the unadjusted relative risks ( RR ) of incident cancer in the Ca + D and Ca-only groups were 0.402 ( P = 0.01 ) and 0.532 ( P = 0.06 ) , respectively . When analysis was confined to cancers diagnosed after the first 12 mo , RR for the Ca + D group fell to 0.232 ( CI : 0.09 , 0.60 ; P < 0.005 ) but did not change significantly for the Ca-only group . In multiple logistic regression models , both treatment and serum 25-hydroxyvitamin D concentrations were significant , independent predictors of cancer risk . CONCLUSIONS Improving calcium and vitamin D nutritional status substantially reduces  all-cancer risk in postmenopausal women . This trial was registered at clinical trials.gov as NCT00352170 BACKGROUND Elevated circulating concentrations of proinflammatory cytokines may contribute to the pathogenesis of congestive heart failure ( CHF ) . In vitro studies suggest that vitamin D suppresses proinflammatory cytokines and increases antiinflammatory cytokines . OBJECTIVE We evaluated the effect of vitamin D supplementation on the survival rate and different biochemical variables in patients with CHF . DESIGN One hundred twenty-three patients r and omly received either 50 mug vitamin D(3)/d plus 500 mg Ca/d [ D(+ ) group ] or placebo plus 500 mg Ca/d [ D(- ) group ] for 9 mo . Biochemical variables were assessed at baseline and after 9 mo . The survival rate was calculated for a follow-up period of 15 mo . RESULTS Ninety-three patients completed the study . Significant treatment effects were observed on logarithmic-transformed serum concentrations of 25-hydroxyvitamin D ( P = 0.001 ) , parathyroid hormone ( P = 0.007 ) , tumor necrosis factor alpha ( P = 0.006 ) , and interleukin 10 ( P = 0.042 ) . 25-Hydroxyvitamin D increased by 26.8 ng/mL in the D(+ ) group but increased only by 3.6 ng/mL in the D(- ) group . Compared with baseline , parathyroid hormone was significantly lower and the antiinflammatory cytokine interleukin 10 was significantly higher in the D(+ ) group after 9 mo . The proinflammatory cytokine tumor necrosis factor alpha increased in the D(- ) group but remained constant in the D(+ ) group . The survival rate did not differ significantly between the study groups during the follow-up period . CONCLUSIONS Vitamin D(3 ) reduces the inflammatory milieu in CHF patients and might serve as a new antiinflammatory agent for the future treatment of the disease . Our data provide evidence for the involvement of an impaired vitamin D-parathyroid hormone axis in the progression of CHF BACKGROUND Indirect evidence suggests that optimal vitamin D status is achieved with a serum 25-hydroxyvitamin D [ 25(OH)D ] concentration > 75 nmol/L. OBJECTIVE We aim ed to determine the intake of vitamin D(3 ) needed to raise serum 25(OH)D to > 75 nmol/L. DESIGN The design was a 6-mo , prospect i ve , r and omized , double-blinded , double-dummy , placebo-controlled study of vitamin D(3 ) supplementation .  Serum 25(OH)D was measured by  radioimmunoassay . Vitamin D(3 ) intake was adjusted every 2 mo by use of an algorithm based on serum 25(OH)D concentration . RESULTS A total of 138 subjects entered the study . After 2 dose adjustments , almost all active subjects attained concentrations of 25(OH)D > 75 nmol/L , and no subjects exceeded 220 nmol/L. The mean ( + /-SD ) slope at 9 wk [ defined as 25(OH)D change/baseline dose ] was 0.66 + /- 0.35 (nmol/L)/(microg/d ) and did not differ statistically between blacks and whites . The mean daily dose was 86 microg ( 3440 IU ) . The use of computer simulations to obtain the most participants within the range of 75 - 220 nmol/L predicted an optimal daily dose of 115 microg/d ( 4600 IU ) . No hypercalcemia or hypercalciuria was observed . CONCLUSIONS Determination of the intake required to attain serum 25(OH)D concentrations > 75 nmol/L must consider the wide variability in the dose-response curve and basal 25(OH)D concentrations . Projection of the dose-response curves observed in this convenience sample onto the population of the third National Health and Nutrition Examination Survey suggests a dose of 95 microg/d ( 3800 IU ) for those above a 25(OH)D threshold of 55 nmol/L and a dose of 125 microg/d ( 5000 IU ) for those below that threshold Background Patients on chronic dialysis are at increased risk of vitamin D deficiency . In observational studies plasma 25-hydroxyvitamin D ( p-25(OH ) D ) levels are inversely correlated with plasma BNP and adverse cardiovascular outcomes . Whether a causal relation exists has yet to be established . The aim of this study was to test the hypothesis that cholecalciferol supplementation improves cardiac function and reduces blood pressure ( BP ) and pulse wave velocity ( PWV ) in patients on chronic dialysis . Methods In a r and omized , place 
    Output:
    
In subgroup analyses , it was shown that the effect of vitamin D supplementation on risk of hypercalcemia , hypercalciuria , or kidney stones was not modified by baseline 25-hydroxyvitamin D , vitamin D dose and duration , or calcium co-supplementation .
CONCLUSIONS Long-term vitamin D supplementation result ed in increased risks of hypercalcemia and hypercalciuria , which were not dose related .
However , vitamin D supplementation did not increase risk of kidney stones .