Serum Vitamin D Concentrations and Cognitive Change Over 20 Years: The Atherosclerosis Risk in Communities Neurocognitive Study.

BACKGROUND/AIMS: 25-hydroxyvitamin D (25[OH]D) concentrations have been associated with cognitive decline and incident dementia in elderly populations; however, these relationships are susceptible to reverse causation. Less is known about the association of midlife 25(OH)D with long-term cognitive decline. METHODS: This was a prospective cohort study of 13,044 participants (mean age 57 years at baseline) in the Atherosclerosis Risk in Communities Study. 25(OH)D was measured from serum collected at baseline (1990-1992) using liquid chromatography tandem high-sensitivity mass spectrometry. Cognition was assessed using 3 neuropsychological tests at 3 time points, which were combined into a composite cognitive Z-score. Multivariable-adjusted linear mixed-effects models with random intercepts and slopes were used to estimate associations between 25(OH)D and cognitive change over 20 years. RESULTS: Compared to persons with sufficient 25(OH)D (≥30 ng/mL), those with deficient (< 20 ng/mL) and intermediate (20-< 30 ng/mL) 25(OH)D concentrations had similar cognitive decline in composite cognitive Z-scores (deficient versus sufficient: -0.035 [95% CI -0.104 to 0.033] and intermediate versus sufficient: -0.029 [95% CI -0.080 to 0.023]). CONCLUSIONS: Lower concentrations of 25(OH)D measured in midlife were not significantly associated with more rapid cognitive decline over a 20-year follow-up period. The results of this prospective study are less susceptible to reverse causation than prior studies.