A recent meta-analysis and review published in Neurology reports that lower vitamin D levels are associated with decreased cognitive function and an increased risk of Alzheimer’s disease (AD).
Dr Cynthia Balion, PhD, and colleagues searched five different databases for research that measure vitamin D status as well as cognitive function.
The authors included 37 studies in their review. Twenty-one cross sectional studies, 10 case-controls, 1 before-after with comparison groups, 2 prospective cohort studies, and 3 randomized controlled trials. The sample sizes of the studies varied greatly from 27 to 17,099 participants.
The authors collected sufficient data to conduct two different meta-analyses. The first compared mean 25(OH)D levels between AD and control groups. Data from 888 participants demonstrated lower serum vitamin D in patients with AD than in controls. Out of the 6 studies included in this specific analysis, all but 1 indicated a lower vitamin D concentration in patients with AD.
The second meta-analysis compared mean Mini-Mental State Examination (MMSE) scores, used to analyze cognitive performance, between participants with vitamin D status <20 ng/mL to those with concentrations ≥20 ng/mL. The authors used data from 2,749 participants from 8 cross-sectional and case-control studies for this analysis. These studies demonstrated that participants with higher vitamin D levels showed higher average MMSE scores.
Of the 2 cohort studies included, the one that included only men reported no significant association between baseline cognitive scores and vitamin D status. However, participants with deficient vitamin D status had an increased risk for cognitive decline over 6 years compared with participants who had sufficient vitamin D levels.
Dr Balion emphasizes the review results differ from two previously published reviews because of the broader inclusion criteria, resulting in a larger number of included studies (37 compared to 5).
The authors stressed the importance of the need for consistent methods of 25(OH)D measurement because of unreliable results for certain assays.
“This systematic review provides sufficient evidence to warrant further investigation to determine if a cause and effect relationship exists between vitamin D and cognitive impairment. To date, no treatment study has examined this question where both vitamin D and cognition were measured over a sufficient period in a large at-risk population.”