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 (25 OHD ) concentration and cognitive performance in a large multi‐ethnic Singaporean population‐based study. We also conducted a meta‐analysis of 25 OHD 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 25 OHD concentration (i.e. ≤10, 10.1–20 and >20 ng mL −1 ). The 25 OHD 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 25 OHD and cognition in Asia (6068 participants; 1179 cognitively impaired cases). Results Participants with 25 OHD 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 25 OHD levels (overall P  <   0.001, P ‐trend < 0.001). Deseasonalized 25 OHD concentration was associated with AMT score (β   =   0.10 per 10 ng mL −1 , P  =   0.035). Vitamin D insufficiency (25 OHD ≤20 ng mL −1 ) was associated with global cognitive impairment ( OR 1.56, P  =   0.028). Specifically, 25 OHD 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 25 OHD difference was −6.83 ng mL −1 (95% confidence interval −11.36; −2.30), indicating lower 25 OHD 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.