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Background: Observational studies have consistently found a link between low serum 25‐hydroxyvitamin D concentration and higher risk of cognitive impairment. Results from randomized controlled trials have been mixed, and few have been conducted in the general population. Methods: We recruited 21,315 community‐dwelling Australians aged between 60 and 84 years to participate in the D‐Health Trial, a randomized, double‐blind, placebo‐controlled trial. The intervention was monthly oral doses of 60,000 international units of vitamin D or placebo for 5 years. We assessed cognitive function in a randomly sampled group of participants aged ≥70 years using the Telephone Interview for Cognitive Status (TICS) at 2 and 5 years after randomization. The primary outcome for this analysis was TICS score; the secondary outcome was the proportion of people who had cognitive impairment (defined as TICS score ≤25). We analyzed data using mixed models (linear and logistic). Results: We interviewed 3887 participants at year 2 and 3614 participants at year 5. The mean TICS score at these time points was 32.3 and 32.2, respectively. Vitamin D supplementation did not affect cognitive function as measured by TICS score (mean difference between vitamin D and placebo groups 0.04; 95% CI −0.14 to 0.23), or alter risk of cognitive impairment (odds ratio 1.00; 95% CI 0.75 to 1.33). Conclusions: Monthly bolus doses of vitamin D supplementation neither enhanced nor hindered cognitive function among older adults. Population‐wide vitamin D supplementation of older adults that are largely vitamin D replete is unlikely to substantially benefit cognition. [ABSTRACT FROM AUTHOR]

Objectives To explore and compare sociodemographic, clinical, and neuropsychiatric determinants of dropout and nonadherence in older people participating in an open-label cluster-randomized controlled trial-the Prevention of Dementia by Intensive Vascular care (pre DIVA) trial-over 6 years. Design Secondary analysis. Setting One hundred sixteen general practices in the Netherlands. Participants Community-dwelling individuals aged 70 to 78 (N = 2,994). Intervention Nurse-led multidomain intervention targeting cardiovascular risk factors to prevent dementia. Measurements The associations between participant baseline sociodemographic (age, sex, education), clinical (medical history, disability, cardiovascular risk), neuropsychiatric (depressive symptoms (Geriatric Depression Scale-15), and cognitive (Mini-Mental State Examination)) characteristics and dropout from the trial and nonadherence to the trial intervention were explored using multilevel logistic regression models. Results Older age, poorer cognitive function, more symptoms of depression, and greater disability were the most important determinants of dropout of older people. The presence of cardiovascular risk factors was not associated with dropout but was associated with nonadherence. Being overweight was a risk factor for nonadherence, whereas people with high blood pressure or a low level of physical exercise adhered better to the intervention. The association between poorer cognitive function and symptoms of depression and dropout was stronger in the control group than in the intervention group, and vice versa for increased disability. Conclusion In a large dementia prevention trial with 6-year follow-up, dropout was associated with older age, poorer cognitive function, symptoms of depression, and disability at baseline. These findings can help to guide the design of future dementia prevention trials in older adults. The associations found between cardiovascular risk factors and nonadherence need to be confirmed in other older populations receiving cardiovascular prevention interventions. [ABSTRACT FROM AUTHOR]