The associations of serum vitamin D status and vitamin D supplements use with all-cause dementia, Alzheimer’s disease, and vascular dementia: a UK Biobank based prospective cohort study

Prior studies on vitamin D and dementia outcomes yielded mixed results and had several important limitations. We aimed to assess the associations of both serum vitamin D status and supplementation with all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VD) incidence. With a prospective cohort study design, we comprehensively assessed the associations of vitamin D and multivitamin supplementation, as well as vitamin D deficiency (25-hydroxyvitamin D (25(OH)D) <30 nmol/L), and insufficiency (25(OH)D 30-<50 nmol/L), with the 14-year incidence of all-cause dementia, AD, and VD in 269,229 participants, aged 55 to 69, from the UK Biobank. Although 5.0% reported regular vitamin D use and 19.8% reported multivitamin use, the majority of participants exhibited either vitamin D deficiency (18.3%) or insufficiency (34.0%). However, vitamin D deficiency was less prevalent among users of vitamin D (6.9%) or multivitamin preparations (9.5%) than among non-users (21.5%). Adjusted Cox regression models demonstrated 19-25% increased risk of all three dementia outcomes for those with vitamin D deficiency (hazard ratio (HR) [95% confidence interval (CI)]: 1.25 (1.16-1.34) for all-cause dementia; 1.19 [1.07-1.31] for AD; 1.24 [1.08-1.43] for VD) and 10-15% increased risk for those with vitamin D insufficiency (HR [95% CI]: 1.11 [1.05-1.18] for all-cause dementia; 1.10 [1.02-1.19] for AD; 1.15 [1.03-1.29] for VD). Regular users of vitamin D and multivitamins had 17% and 14% lower risk of AD (HR [95% CI]: 0.83 [0.71-0.98]) and VD (HR [95% CI]: 0.86 [0.75-0.98]) incidence, respectively. While our findings indicate potential benefits of vitamin D supplementation for dementia prevention, randomized controlled trials are essential for definitive evidence.