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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Myth-buster

Five years of up to 3,200 IU/day vitamin D didn’t cut dementia risk in healthy older adults — only 13 cases occurred in the high-dose group versus 18 with placebo.

This well-designed, five-year Finnish trial found no statistically significant protection against dementia from vitamin D in people who were already replete — but with only 45 total dementia cases across all arms, the study lacked the power to detect a small effect, so the question isn't settled.

In a double-blind trial of 550 healthy, vitamin-D-sufficient older adults, neither 1,600 nor 3,200 IU/day of vitamin D for about five years reduced the number who developed dementia or Alzheimer's compared to placebo. The hazard ratios (0.77 and 0.72) suggest a possible slight reduction, but the confidence intervals were wide and crossed 1.0, meaning chance could explain the difference. Because this is one of the first rigorous studies on this specific question and the total number of dementia diagnoses was small, we need larger trials before drawing firm conclusions.

Where this fits in the evidence

This is among the first studies we've indexed on Vitamin D for Reduced Dementia Incidence — treat it as an early signal until more research accumulates.

The study

The Effect of Vitamin D3 Supplementation on the Incidence of Diagnosed Dementia Among Healthy Older Adults-The Finnish Vitamin D Trial.

  • Randomized Controlled Trial (RCT)
  • n = 550
  • 2025-04-17
  • The journals of gerontology. Series A, Biological sciences and medical sciences
More on Vitamin DMore on Reduced Dementia Incidence

This is a plain-language summary of a research finding, not medical advice. Pillser surfaces research signals to help you decide what's worth investigating — always consult a qualified professional before changing what you take.

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