Association between serum 25(OH) vitamin D and the risk of cognitive decline in older women

Abstract

Background: Results of prospective studies examining the association between 25 hydroxyvitamin D (25[OH]D) levels and cognitive decline have been inconsistent. We tested the hypothesis that lower 25(OH)D levels are associated with a greater likelihood of cognitive impairment and risk of cognitive decline.

Methods: The study is a cross-sectional and longitudinal analysis of a prospective cohort of 6,257 community-dwelling elderly women followed for 4 years. Global cognitive function was measured by the Modified Mini-Mental State Examination and executive function was measured by Trail Making Test Part B (Trails B). Cognitive impairment at baseline was defined as a score >1.5 SD below the sample mean; cognitive decline was defined as decline from baseline to follow-up >1 SD from mean change in score.

Results: Women with very low vitamin D levels had an increased odds of global cognitive impairment at baseline: odds ratio (95% confidence interval), 1.60 (1.05-2.42) for women with 25(OH)D <10 ng/mL (25 nmol/L) compared with those with 25(OH)D levels ≥30 ng/mL (75 nmol/L). Compared with women with baseline 25(OH)D level ≥30 ng/mL (75 nmol/L), women with lower levels had an increased risk of global cognitive decline: odds ratio (95% confidence interval), 1.58(1.12-2.22) for women with levels <10 ng/mL (25 nmol/L), and 1.31 (1.04-1.64) for those with levels 10-19.9 ng/mL (25-49 nmol/L). Levels of 25(OH)D were not associated with executive cognitive function.

Conclusions: Low 25(OH)D levels among older women were associated with a higher odds of global cognitive impairment and a higher risk of global cognitive decline.

Figures

Figure 1.

Study roadmap.

Figure 2.

Change in cognitive function by category of serum 25(OH)D concentration. Results are based on a random-effects model with multivariate adjustment for clinic site, season of blood collection, age at baseline, years of education, self-reported health status, instrumental activity of daily living impairments, smoking status at baseline, body mass index, history of hypertension, history of diabetes, depression, and baseline cognitive score. P values for comparison with >30ng/mL (reference): 20–29 ng/mL p= .1630; 10–19 ng/mL p = .7969; <10 ng/mLp = .0385.