The effect of vitamin D₃ supplementation on the incidence of diagnosed dementia among healthy older adults – the Finnish Vitamin D Trial

Some short-term vitamin D supplementation trials suggest benefits on cognitive performance, but apart from observational studies, there is little evidence whether long-term vitamin D supplementation can prevent development of dementia. We investigated whether vitamin D₃ supplementation could affect the incidence of diagnosed dementia in a generally healthy population.

The study included 2492 participants from the Finnish Vitamin D Trial, free of diagnosed dementia at baseline. They were randomized to placebo, 1600 IU/day or 3200 IU/day of vitamin D₃ arm for up to 5 years. Incident diagnoses of dementia were obtained from the national care registries.

The mean age of the participants at baseline was 68.2 y and 42.8% were female. During the mean follow-up of 4.2 y, 18 participants in the placebo arm, 14 participants in the 1600 IU/day arm (compared to placebo, hazard ratio [HR]=0.77, 95% confidence interval [CI] 0.38-1.55) and 13 participants in the 3200 IU/day arm (HR=0.72, 95% CI 0.35-1.48) were diagnosed with dementia. Of the diagnoses, 29 were Alzheimer’s disease, without statistically significant differences in the event rates between the three arms. Age, sex, or body mass index did not modify the effects. In the subgroup of 550 participants, the mean baseline serum 25-hydroxyvitamin D concentration was 74.8 nmol/L. After 12 months, the mean concentrations were 73.0, 99.7 and 120.4 nmol/L, in the placebo, 1600 IU/day and 3200 IU/day arms, respectively.

Five-year, medium-dose or high-dose vitamin D₃ supplementation did not affect the dementia incidence in this largely vitamin D sufficient older population.