Vitamin D insufficiency and cognitive impairment in Asians: a multi-ethnic population-based study and meta-analysis.

BACKGROUND: The relationship between vitamin D insufficiency and cognitive impairment remains equivocal in Asians. We examined the association between circulating 25-hydroxyvitamin D (25OHD) concentration and cognitive performance in a large multi-ethnic Singaporean population-based study. We also conducted a meta-analysis of 25OHD concentrations amongst cognitively impaired older adults in Asia.

METHODS: Our population-based cross-sectional study included 2273 persons ≥60 years of age from the Singapore Epidemiology of Eye Diseases (SEED) study (mean ± SD age 70.4 ± 6.2 years; 44.7% female), who were categorized according to 25OHD concentration (i.e. ≤10, 10.1-20 and >20 ng mL(-1) ). The 25OHD concentration was measured and adjusted to reflect a deseasonalized value. Cognition was assessed using the total and domain scores of the Abbreviated Mental Test (AMT). Global cognitive impairment was defined as AMT score of ≤6 if 0-6 years of education and AMT score of ≤8 if >7 years of education. Fully adjusted multivariate models were used. We included seven studies in a meta-analysis of 25OHD and cognition in Asia (6068 participants; 1179 cognitively impaired cases).

RESULTS: Participants with 25OHD levels >20 ng mL(-1) (n = 1302) had higher AMT total scores (mean ± SD 8.5 ± 1.9) and were less likely to have cognitive impairment (14.1%) than participants with lower 25OHD levels (overall P < 0.001, P-trend < 0.001). Deseasonalized 25OHD concentration was associated with AMT score (β = 0.10 per 10 ng mL(-1) , P = 0.035). Vitamin D insufficiency (25OHD ≤20 ng mL(-1) ) was associated with global cognitive impairment (OR 1.56, P = 0.028). Specifically, 25OHD concentration correlated with semantic memory (r = 0.08, P = 0.009) and orientation in time (r = 0.09, P = 0.003). In the meta-analysis, the pooled mean 25OHD difference was -6.83 ng mL(-1) (95% confidence interval -11.36; -2.30), indicating lower 25OHD concentrations amongst cognitively impaired compared to cognitively healthy participants in Asia.

CONCLUSION: Vitamin D insufficiency is associated with a greater likelihood of and more severe cognitive impairment in Asian populations.