Effects of Vitamin D Supplementation on Cognitive Function in Older Adults: A Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Methodology–Assessed Systematic Review and Meta-Analysis of Randomized Clinical Trials

CONTEXT: The increasing number of older adults suffering from cognitive decline is a global public health challenge. Current evidence suggests that vitamin D supplementation may be related to better cognitive performance. However, the results of randomized controlled trials (RCTs) have been contradictory. A previous review on this topic included younger study participants, combined nutrient interventions, and lack of appropriate control group to evaluate the net effect of vitamin D. OBJECTIVE: The aim of this systematic review and meta-analysis was to investigate the impact of vitamin D3 supplementation on cognition in individuals ≥60 years old. DATA SOURCES: The systematic search was performed in PubMed, Scopus, and ISI Web of Sciences database until September 2023 for eligible studies. In the final analysis, 9 RCTs were included. DATA EXTRACTION: The pooled effect was assessed using random effects model with standard mean differences (SMDs) and 95% CIs. The quality of RCTs and certainty assessment of each outcome were evaluated via the Risk of Bias 2 tool and Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology, respectively. DATA ANALYSIS: The results showed that compared with controls, vitamin D significantly improved global cognition (SMD, 0.66; 95% CI, 0.02-1.30; P = .04), language (SMD, 1.29; 95% CI, 1.10-1.47; P < .001), working memory (SMD= 1.58; 95% CI, 1.40-1.77; P < .001), and visuospatial function (SMD, 0.31; 95% CI, 0.14-0.48; P < .001) in older adults. While no significant enhancement in the domains of executive function (SMD, 0.10; 95% CI, -0.04 to 0.25; P = .16), attention (SMD, 0.02; 95% CI, -0.33 to 0.38; P = .89), and perceptual speed (SMD= 0.09; 95% CI, -0.27 to 0.45; P = .6) was found. CONCLUSIONS: Vitamin D supplementation can be associated with improvement in cognitive function in older adults. Further RCTs in older people are needed to confirm the benefits of vitamin D supplementation on cognition. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. 42023484900.