***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: BACKGROUND Participation in leisure activities has been associated with a lower risk of dementia .  It is unclear whether increased participation in leisure activities lowers the risk of dementia or participation in leisure activities declines during the pre clinical phase of dementia . METHODS We examined the relation between leisure activities and the risk of dementia in a prospect i ve cohort of 469 subjects older than 75 years of age who resided in the community and did not have dementia at base line . We examined the frequency of participation in leisure activities at enrollment and derived  cognitive-activity and physical-activity scales in which the units of measure were activity-days per week . Cox proportional-hazards analysis was used to evaluate the risk of dementia according to the base-line level of participation in leisure activities , with adjustment for age , sex , educational level , presence or absence of chronic medical illnesses , and base-line cognitive status . RESULTS Over a median follow-up period of 5.1 years ,  dementia  developed in 124 subjects ( Alzheimer 's disease in 61 subjects , vascular dementia in 30 , mixed dementia in 25 , and other types of dementia in 8) . Among leisure activities , reading , playing board games , playing musical instruments , and dancing were associated with a reduced risk of dementia . A one-point increment in the cognitive-activity score was significantly associated with a reduced risk of dementia ( hazard ratio , 0.93 [ 95 percent confidence interval , 0.90 to 0.97 ] ) , but a one-point increment in the physical-activity score was not ( hazard ratio , 1.00 ) . The association with the cognitive-activity score persisted after the exclusion of the subjects with possible pre clinical dementia at base line . Results were similar for Alzheimer 's disease and vascular dementia . In linear mixed models , increased participation in cognitive activities at base line was associated with reduced rates of decline in memory . CONCLUSIONS Participation in leisure activities is associated with a reduced risk of dementia , even after adjustment for base-line cognitive status and after the exclusion of subjects with possible pre clinical dementia . Controlled trials are needed to assess the protective effect of cognitive leisure activities on the risk of dementia The objective of this study was to investigate the relation between the peripheral concentrations of the adrenal steroid hormones cortisol and dehydroepi and rosterone sulfate ( DHEAS ) and cognitive impairment and decline . A prospect i ve study design was used . The setting was a suburb of Rotterdam , The Netherl and s. The study population consisted of a sample of 189 healthy participants from the population -based Rotterdam Study , aged 55 - 80 yr , who were invited for an additional examination . Follow-up examinations took place 1.9 yr after baseline , on the average . We determined fasting blood levels of DHEAS before dexamethasone administration and of cortisol and corticosteroid-binding globulin before and after the administration of 1 mg dexamethasone overnight . The  30-point Mini-Mental State Examination ( MMSE )  was used to assess cognition . The associations with cognitive impairment ( MMSE score of < 26 ; 6 % of the sample ) and cognitive decline ( drop in MMSE score of > 1 point/yr ; 24 % ) were estimated using logistic regression , with adjustment for age , sex , education , and depressive symptoms . An increase of 1 SD in the estimate of free cortisol ( SD = 30.3 ) was associated with cognitive impairment , although not significantly [ odds ratio ( OR ) = 1.5 ; 95 % confidence interval ( CI ) , 0.9 - 2.4 ] . A 1 SD increase in the natural logarithm of cortisol after the administration of 1 mg dexamethasone ( SD = 0.68 ) was associated with an OR for cognitive decline of 1.5 ( 95 % CI , 1.0 - 2.3 ) . A 1 SD increase in DHEAS ( SD = 2.10 micromol/L ) was inversely , but nonsignificantly , related to cognitive impairment ( OR = 0.5 ; 95 % CI , 0.2 - 1.1 ) and cognitive decline ( OR = 0.6 ; 95 % CI , 0.4 - 1.1 ) . The ratio of free cortisol over DHEAS was significantly related to cognitive impairment ( OR = 1.8 ; 95 % CI , 1.0 - 3.2 ) . This prospect i ve study among healthy elderly subjects suggested that basal free cortisol levels were positively related to cognitive impairment , and cortisol levels after dexamethasone treatment were related to cognitive decline . There was an inverse , but nonsignificant , association between DHEAS and cognitive impairment and decline We investigated the long-term influence of physical activity on the risk of dementia in an elderly Japanese population . A total of 803 community-dwelling elderly Japanese individuals without dementia aged ≥65 years were followed prospect ively for 17 years . Physically active status was defined as engaging in exercise at least one or more times per week during leisure time , and participants were divided into an active group and an inactive group by the presence or absence of such physical activity . The risk estimates of physical activity on the development of all-cause dementia and its subtypes were computed using a Cox proportional hazards model . During the follow-up , 291 participants developed all-cause dementia . Of these , 165 had Alzheimer ’s disease ( AD ) , 93 had vascular dementia ( VaD ) , and 47 had other dementia . Compared with the inactive group , the active group showed significantly lower crude incidence of AD ( 21.8 vs. 14.2 per 1000 person-years , p = 0.01 ) , but no significant differences were observed for all-cause dementia ( 35.6 vs. 30.5 , p = 0.17 ) , VaD ( 11.3 vs. 9.8 , p = 049 ) , and other dementia ( 4.6 vs. 7.1 , p = 0.15 ) . After adjusting for potential confounders , the relationship  between physical activity and risk of AD remained significant ( adjusted hazard ratio 0.59 , 95 % confidence interval 0.41–0.84 , p = 0.003 ) . Our findings suggest that physical activity  reduces the long-term risk of dementia , especially AD , in the general Japanese population Objective : This study evaluated the protective role of physical activity ( PA ) against  cognitive impairment ( CI ) in the oldest old ( age ≥ 85 ) . Method : Prospect i ve data on 66 optimally healthy , oldest old adults ( mean age 88.5 ) were analyzed using survival analysis . Results : In all , 12 men and 11 women reported exercising > 4 hours per week , and 38 participants developed CI ( mean onset age 93 ; mean follow-up 4.7 years ) . The effect of exercise was modified by gender . In more active women ( > 4 hours/week ) , the risk of CI was reduced by 88 % ( 95 % confidence interval 0.03 , 0.41 ) compared to those less active . Less active women had 2 times the incidence rate of CI compared to less active men and almost 5 times the rate compared to active women . Discussion : This study demonstrates the beneficial effects of exercise  on healthy brain aging even in the oldest old and emphasizes the importance of increasing PA in older women BACKGROUND Alzheimer disease ( AD ) is considered a leading cause of death , but few studies have examined the contribution of AD to mortality based on follow-up of representative US cohorts . OBJECTIVE To examine mortality rates , duration of survival , causes of death , and the contribution of AD  to the risk of mortality in an aging community-based cohort , controlling for other predictors . DESIGN Fifteen-year prospect i ve epidemiological study . Mortality rates per 1000 person-years and the population -attributable risk of mortality were determined . Cox proportional hazards models were used to estimate relative risk of mortality due to AD , adjusting for relevant covariates . Death certificates were abstract ed for listed causes of death . SETTING A largely blue-collar rural community in southwestern Pennsylvania . PARTICIPANTS A community-based cohort of 1670 adults 65 years and older at study enrollment . MAIN OUTCOME MEASURE Mortality . RESULTS In the overall cohort , AD was a significant predictor of mortality , with a hazard ratio of 1.4 after adjusting for covariates . The population -attributable risk of mortality from AD was 4.9 % based on the same model . Examining the sexes separately , AD increased mortality risk only among women . Death certificates of AD subjects were more likely to list dementia/AD , other brain disorders , pneumonia , and dehydration , and less likely to include cancer . CONCLUSIONS Alzheimer disease was responsible for 4.9 % of the deaths in this elderly cohort . Alzheimer disease increased the risk of mortality 40 % in the cohort as a whole and separately in women but not in men . The mean ( SD ) duration of survival with AD was 5.9 ( 3.7 ) years , and longer with earlier age at onset CONTEXT Dementia is common , costly , and highly age related . Little attention has been paid to the identification of modifiable lifestyle habits for its prevention . OBJECTIVE To explore the association between physical activity and the risk of cognitive impairment and dementia .  DESIGN , SETTING , AND SUBJECTS Data come from a community sample of 9008 r and omly selected men and women 65 years or older , who were evaluated in the 1991 - 1992 Canadian Study of Health and Aging , a prospect i ve cohort study of dementia . Of the 6434 eligible subjects who were cognitively normal at baseline , 4615 completed a 5-year follow-up .  Screening and clinical evaluations were done at both waves of the study . In 1996 - 1997 , 3894 remained without cognitive impairment , 436 were diagnosed as having cognitive impairment-no dementia , and 285 were diagnosed as having dementia . MAIN OUTCOME MEASURE Incident cognitive impairment and dementia by levels of physical activity at baseline . RESULTS Compared with no exercise , physical activity was associated with lower risks of cognitive impairment , Alzheimer disease , and dementia of any type . Significant trends for increased protection with greater physical activity were observed . High levels of physical activity were associated with reduced risks of cognitive impairment ( age- , sex- , and education-adjusted odds ratio , 0.58 ; 95 % confidence interval , 0.41 - 0.83 ) , Alzheimer disease ( odds ratio , 0.50 ; 95 % confidence interval , 0.28 - 0.90 ) , and dementia of any type ( odds ratio , 0.63 ; 95 % confidence interval , 0.40 - 0.98 ) . CONCLUSION Regular physical activity could represent an important and potent protective factor for cognitive decline and dementia in elderly persons Several studies have associated physical activity with the risk of dementia , but mostly did so during short follow-up . It remains unclear whether physical activity also affects dementia during longer follow-up . We examined the association between physical activity and risk of dementia during a follow-up period up to 14 years . From 1997 to 1999 , physical activity was assessed using a vali date d question naire in 4,406 elderly persons ( age range 61–97 ) from the prospect i ve , population -based Rotterdam Study . Follow-up for dementia was complete until January 1 , 2011 . We used Cox proportional hazards models to assess the association between physical activity and incident dementia . Next , we stratified follow-up time using a cut-off of 4 years . We separately investigated dementia due to Alzheimer disease . During 38,631 person-years , 583 participants developed dementia . When adjusting for age and sex , we found a borderline significant association between  higher physical activity and lower risk of dementia ( HR 0.95 ; 95 % CI 0.87–1.04 ) . This association was confined to follow-up up to 4 years ( HR 0.82 ; 95 % CI 0.71–0.95 ) , and not to follow-up of at least 4 years ( HR 1.04 ; 95 % CI 0.93–1.16 ) . Additional adjustments only slightly attenuated the associations . A similar pattern was present for Alzheimer disease . We found a higher level of physical activity  to be associated with a lower risk of dementia . This association was confined to follow-up for up to 4 years and not to longer follow-up , suggesting either a role for reverse causality or only a short term effect of late-life physical activity in an elderly population Objectives : To provide up date d estimates of Alzheimer disease ( AD ) dementia prevalence in the United States from 2010 through 2050 . Methods : Probabilities of AD dementia incidence were calculated from a longitudinal , population -based study including substantial numbers of both black and white participants . Incidence probabilities for single year of age , race , and level of education were calculated using weighted logistic regression and AD dementia diagnosis from 2,577 detailed clinical evaluations of 1,913 people obtained from stratified r and om sample s of previously disease-free individuals in a population of 10,800 . These were combined with US mortality , education , and new US Census Bureau estimates of current and future population to estimate current and future numbers of people with AD dementia in the United States . Results : We estimated 
    Output:
    
Our findings suggest  that physical activity is more protective against Alzheimer 's disease than it is for all-cause dementia , vascular dementia , and cognitive decline