You will be presented with a collection of medical randomized controlled trial (RCT) reports addressing a shared clinical question -- for instance, the efficacy of a medical intervention on a disease or condition. Given the titles and abstracts of these reports, your task is to generate the conclusion of the systematic review article synthesizing the key findings. Your conclusion should be a few sentences long. In your response, include only the conclusion and no other text. The RCT reports are below.



Title 1:
Longitudinal assessment of serum free testosterone concentration predicts memory performance and cognitive status in elderly men.
Abstract 1:
Circulating testosterone ( T ) levels have behavioral and neurological effects in both human and nonhuman species . Both T concentrations and neuropsychological function decrease substantially with age in men . The purpose of this prospect i ve , longitudinal study was to investigate the relationships between age-associated decreases in endogenous serum T and free T concentrations and declines in neuropsychological performance .  Participants were volunteers from the Baltimore Longitudinal Study of Aging , aged 50 - 91 yr at baseline T assessment . Four hundred seven men were followed for an average of 10 yr , with assessment s of multiple cognitive domains and contemporaneous determination of serum total T , SHBG , and a free T index ( FTI ) . We administered  neuropsychological tests of verbal and visual memory , mental status , visuomotor scanning and attention , verbal knowledge/ language , visuospatial ability , and depressive symptomatology .  Higher FTI was associated with better scores on visual and verbal memory , visuospatial functioning , and visuomotor scanning and a reduced rate of longitudinal decline in visual memory . Men classified as hypogonadal had significantly lower scores on measures of memory and visuospatial performance and a faster rate of decline in visual memory . No relations between total T or the FTI and measures of verbal knowledge , mental status , or depressive symptoms were observed . These results suggest a possible beneficial relationship between circulating free T concentrations and specific domains of cognitive performance in older men


Title 2:
Sex hormones and cognitive function in older men.
Abstract 2:
OBJECTIVES Recent studies have suggested that estrogen may improve cognitive function or prevent  cognitive decline in older women . Little research has been conducted on exogenous or endogenous sex hormones and cognition in older men , yet it has been hypothesized that testosterone , either directly or by conversion to estrogens , may improve cognitive function . We investigated whether serum level of testosterone and estradiol is associated with cognition in older community-dwelling men . DESIGN A cross-sectional study . SETTING Population -based listings in the Monongahela Valley near Pittsburgh , Pennsylvania . PARTICIPANTS Three hundred ten men ( mean age + /- st and ard deviation = 73.0 + /- 7.1 ) who were part of a cohort study . MEASUREMENTS We measured cognitive function using the  Mini-Mental State Examination ( MMSE ) , Trails B , and Digit Symbol . Sex hormone levels were determined by radioimmunoassay from serum obtained at the time of cognitive testing and analyzed by tertile . RESULTS No consistent association between total testosterone level and cognitive test scores was observed . However , men with high bioavailable ( loosely protein-bound ) testosterone had better cognitive test scores on all three tests ( P < or = .001 ) . Total estradiol levels were associated with worse cognitive scores on Digit Symbol ( P < .001 ) and Trails B ( P = .002 ) , but bioavailable estradiol levels were not associated with cognitive function . Level of sex hormone binding globulin ( SHBG ) was negatively associated with cognitive scores on all three tests ( P < or = .001 ) . After adjusting for age and education , the statistical significance lessened for bioavailable testosterone ( MMSE , P = .086 ; Digit Symbol , P = .047 ; Trails B , P = .076 ) and became nonsignificant for SHBG ( all cognitive tests P>.10 ) . CONCLUSIONS Our findings support the hypothesis that higher levels of bioavailable testosterone , but not of bioavailable estradiol , are associated with better cognitive function in older men . In addition , bioavailable measures of testosterone may better reflect hormone levels available to the brain and thus be more closely associated with central nervous system outcomes such as cognition . Future studies , especially r and omized trials , should be undertaken to determine whether testosterone may protect against cognitive decline in older men


Title 3:
Serum levels of estradiol and testosterone and performance in different cognitive domains in healthy elderly men and women
Abstract 3:
Sex hormones could protect against age-related cognitive decline in elderly men and women . We investigated the relationships between serum total testosterone ( TT ) , total estradiol ( TE2 ) levels and cognitive function in 145 non-demented elderly volunteers ( aged 61 - 91 years ) who were not using hormone replacement therapy ( HRT ) .  Women ( n=66 ) were better at verbal recall than men ( n=79 ) and men were slightly better at naming . There was a positive relationship between serum levels of TE2 and verbal list recall but not with other verbal memory tests ( e.g. Verbal Paired Associates ) in women . There was a negative relationship of serum TT levels with verbal recall . Surprisingly , women who were in the upper age tertile ( > 77 years of age ) were better at verbal recall than men and than women younger than 72 ; this effect was independent of hormone levels . Men between 61 and 72 years of age showed a positive relationship between high TE2 levels and Spatial Span performance and between high TT levels and speed of information processing , while for women of this age-group , a negative relationship was found . These preliminary results were unchanged when controlling for education , sex hormone binding globulin levels , body mass index , depression , daily alcohol use and smoking . In sum , not all cognitive functions were better with higher levels of sex steroids and effects seemed to be modified by sex ; the sex-sensitive tests showing the clearest effects . More research is required to investigate whether there is a window of time in which hormone therapy could be beneficial for middle-aged men


Title 4:
Alzheimer disease in the US population: prevalence estimates using the 2000 census.
Abstract 4:
CONTEXT Current and future estimates of Alzheimer disease ( AD ) are essential for public health planning . OBJECTIVE To provide prevalence estimates of AD for the US population from 2000 through 2050 . DESIGN Alzheimer disease incidence estimates from a population -based , biracial , urban study , using a stratified r and om sampling design , were converted to prevalence estimates and applied to US Census Bureau estimates of US population growth . SETTING A geographically defined community of 3 adjacent neighborhoods in Chicago , Ill , applied to the US population . PARTICIPANTS  Alzheimer disease incidence was measured in 3838 persons free of AD at baseline ; 835 persons were evaluated for disease incidence . Main Outcome Measure Current and future estimates of prevalence of clinical ly diagnosed AD in the US population . RESULTS In 2000 , there were 4.5 million persons with AD in the US population . By 2050 , this number will increase by almost 3-fold , to 13.2 million . Owing to the rapid growth of the oldest age groups of the US population , the number who are 85 years and older will more than quadruple to 8.0 million . The number who are 75 to 84 years old will double to 4.8 million , while the number who are 65 to 74 years old will remain fairly constant at 0.3 to 0.5 million . CONCLUSION The number of persons with AD  in the US population will continue to increase unless new discoveries facilitate prevention of the disease


Title 5:
Postmenopausal hormone therapy and cognitive outcomes: The Women's Health Initiative Memory Study (WHIMS)
Abstract 5:
This review discusses major findings from the Women 's Health Initiative Memory Study ( WHIMS ) . WHIMS reported hormone therapy (HT)--conjugated equine estrogen ( CEE ) with or without medroxyprogesterone acetate (MPA)--increased the risk for dementia ( HR 1.76 [ 95 % CI , 1.19 - 2.60 ] ; P=0.005 ) and global cognitive decline , with a mean decrement relative to placebo of 0.21 points on the Modified Mini Mental State Examination ( 3MS ) ( P=0.006 ) in women age 65 and older . A subset of WHIMS participants joined the ancillary WHI Study of Cognitive Aging ( WHISCA ) trials , in which domain-specific cognitive tests and mood were measured annually . Compared with placebo , CEE+MPA had a negative impact on verbal memory over time ( P=0.01 ) ; and CEE-Alone was associated with lower spatial rotational ability ( P < or = 0.01 ) at the initial assessment , but the difference diminished over time . The ancillary WHIMS-MRI study measured sub clinical cerebrovascular disease to possibly explain the negative cognitive findings reported by WHIMS and the increased clinical stroke in older women reported by the WHI . WHIMS-MRI reported that while CEE+MPA and CEE-Alone were not associated with increased ischemic brain lesion volume relative to placebo ; both CEE+MPA and CEE-Alone were associated with lower mean brain volumes in the hippocampus ( P=0.05 ) ; frontal lobe ( P=0.004 ) ; and total brain ( P=0.07 ) . HT-associated reductions in hippocampal volumes were greatest in women with baseline 3MS scores < or = 90


Title 6:
Serum estrogen levels, cognitive performance, and risk of cognitive decline in older community women.
Abstract 6:
OBJECTIVE To determine the association between serum estrogen levels , cognitive performance , and risk of cognitive decline in older women . DESIGN Prospect i ve cohort study with an average follow-up of 5 years . SETTING Clinical centers in Baltimore , MD , Minneapolis , MN , Portl and , OR , and the Monongahela Valley in Pennsylvania . PARTICIPANTS 532 women aged 65 years or older who were the controls from two nested case-control studies in the ongoing Study of Osteoporotic Fractures . OUTCOME MEASURES Three cognitive tests -- a modified Mini-Mental Status Exam , Digit Symbol , and Trails B -- were administered at study initiation and were then repeated approximately 5 years later . Estrone and estradiol levels were determined by radioimmunoassay at two laboratories from baseline stored serum . RESULTS The characteristics of the women in the four serum estrogen quartiles did not differ except that body weight and change in weight since age 50 increased directly with higher quartile of serum estrogen ( P < .001 , for both estrone and estradiol ) . Initial cognitive performance on all three tests did not differ consistently by quartile of estradiol or by the estradiol to estrone ratio . Women in the higher estrone quartiles had 15 % lower ( worse ) scores on Digit Symbol compared with the lower quartiles ( P=.004 ) but there was no difference by quartile on the modified MMSE or on Trails B. Cognitive function test scores declined over the 5 years of follow-up . There was no difference in amount of change by quartile of estradiol , but women in the higher estrone quartiles had greater reduction of scores on Trails B compared with those in the lower quartiles ( P=.012 ) , even after adjusting for age , education , depression , stroke history , weight , and change in weight since age 50 . The age-adjusted odds of cognitive decline ( defined as tenth percentile of women with the largest decline in cognitive performance ) did not vary across quartile of estrone or estradiol . CONCLUSIONS Endogenous estrogens are not associated consistently with cognitive performance or risk of cognitive decline on a selected battery of cognitive tests in older community-dwelling women . Worse performance on two cognitive tests among women with higher estrone levels was surprising and warrants further investigation


Title 7:
Sex hormones and cognitive decline in elderly men
Abstract 7:
Decline of cognitive function with age may be due , in part , to hormonal changes and it has been hypothesized that higher levels of endogenous sex hormones preserve brain function . The aim of this prospect i ve cohort study was to determine the relative contribution of endogenous sex hormones to cognitive decline in a population -based sample of 242 elderly men aged 73 - 91 at baseline .  Endogenous sex hormone levels were measured at baseline and participants underwent a cognitive assessment at baseline and at follow-up after 4 years .  Higher estradiol ( total and bioavailable ) and estrone levels were associated with an increased risk of cognitive decline in elderly men independent of age , cardiovascular risk factors , atherosclerosis , and APOE genotype . These findings do not support the hypotheses that higher levels of endogenous sex hormones preserve brain function
Findings were mixed , although potential patterns were identified .
Estradiol levels were potentially associated with benefits to episodic memory , semantic memory , verbal memory , and verbal learning in females only .
The association between testosterone and cognitive function was mixed in both genders .