Association between vitamin D supplement use and cognitive functioning: a longitudinal cohort study.

OBJECTIVES: The real-world evidence on the association between vitamin D supplementation and cognitive outcomes has been scant and controversial. We aimed to investigate the longitudinal association between vitamin D supplement use and subsequent cognitive functioning among US older adults.

DESIGN: Prospective cohort study.

SETTING: A nationally representative ageing cohort in USA: the Health and Retirement Study (HRS).

PARTICIPANTS: Participants were drawn from the HRS wave 12 and included respondents who had complete data on dietary supplement use and cognitive assessment. A total of 5065 participants (mean age: 67.5±10.2 years, 61.6% female, 76.6% White ethnicity) were included, of whom 2004 (39.6%) participants were vitamin D supplement users.

PRIMARY AND SECONDARY OUTCOME MEASURES: Change in cognitive function scores over 6 years of follow-up (from HRS waves 12-15), estimated by linear mixed model adjusted for multiple covariates.

RESULTS: Compared with non-users, vitamin D users had an accelerated decline in global cognitive function (difference in the rate of change: -0.052 points/year; 95% CI -0.092 to -0.013, p=0.010) and in executive function score (difference: -0.021 points/year; 95% CI -0.037 to -0.005, p0.010). Sensitivity analysis suggested that accelerated cognitive decline was only observed among supplement users with normal baseline serum 25(OH)D level (p=0.004), but not the group with insufficient/deficient levels (p=0.826).

CONCLUSIONS: Our findings do not support vitamin D supplementation as a means of preventing or slowing cognitive decline in older people with adequate vitamin D status. While healthcare providers should encourage adequate vitamin D intake from dietary sources and moderate sun exposure, caution should be taken when recommending such supplements to older adults without a clear indication for it.