The D-Health trial

D-Health showed that a monthly 60,000 IU (international units) dose did not lower death rates in people who already have reasonable vitamin D levels. If you take vitamin D, take it daily rather than in large occasional doses.

What the trial tested

Vitamin D is a fat-soluble vitamin the skin makes in sunlight and that some foods and supplements supply; blood tests measure it as 25-hydroxyvitamin D, in nanomoles per litre (nmol/L). D-Health randomised 21,315 older Australians to 60,000 IU of vitamin D once a month, or placebo, with death from any cause as its main outcome.^[1]

The people enrolled were mostly not deficient: during the trial, the placebo group's blood level averaged 77 nmol/L,^[2] comfortably above the 50 nmol/L usually treated as enough.^[3] So, like the US VITAL trial, it tests topping up people who already have enough, not correcting a deficiency.

The main result: no effect on death

Death from any cause was not lowered. The hazard ratio was 1.04, meaning the risk at any point was fractionally higher on vitamin D; the 95% confidence interval, the range where the true effect most plausibly lies, ran from 0.93 to 1.18, so the result is compatible with no effect.^[4]

A 2026 modelling study re-ran D-Health and VITAL as simulated trials in UK Biobank data and reproduced the null results, but projected about 20–25% lower mortality in deficient people (hazard ratios 0.75–0.79).^[5] That projection rests on observational data, not on a trial, and a corrected genetic analysis found no such effect (see Vitamin D).

The secondary results

• Heart and stroke. Major cardiovascular events were about 9% lower, a borderline result still compatible with no effect (hazard ratio 0.91, confidence interval 0.81–1.01). Heart attacks were about 19% lower (hazard ratio 0.81, confidence interval 0.67–0.98), but that was a secondary finding.^[6]
• Cancer deaths: a possible warning sign. Cancer deaths were about 15% higher on vitamin D, a result compatible with no effect (hazard ratio 1.15, confidence interval 0.96–1.39). Leaving out the first two years, an exploratory analysis, they were about 24% higher (hazard ratio 1.24, confidence interval 1.01–1.54).^[7]
• New cancers. Not raised (hazard ratio 1.02, confidence interval 0.95–1.10).^[8]
• Fractures. Not lowered or raised (hazard ratio 0.94, confidence interval 0.84–1.06).^[9]

Why the dosing schedule matters

D-Health is one of several trials suggesting that large intermittent doses behave differently from steady daily ones. A 2023 pooled analysis of 14 trials found cancer deaths about 12% lower in the 10 trials that dosed daily, but no benefit in the 4 trials that used large intermittent doses (relative risk 1.07, read like a hazard ratio; confidence interval 0.91–1.24). That is a subgroup finding, not proof.^[10] In a separate trial, a single 500,000 IU dose once a year raised falls by 15% and fractures by 26% in women aged 70 and over at high fracture risk.^[11] The 2024 Endocrine Society guideline prefers daily doses over large intermittent ones for people over 50 who need vitamin D.^[12]

The cancer-death signal in D-Health is not established: the overall result was compatible with chance, and new cancers did not rise. But it fits the wider pattern: large intermittent doses have shown no benefit in pooled trials, and one yearly-dose trial raised falls and fractures. Large intermittent doses are at best useless and at worst harmful.

What to do

1. Don't take large monthly or yearly doses of vitamin D. In D-Health they did not lower deaths and may have raised cancer deaths.
2. If you are low, correct it with a daily dose and retest; see Vitamin D for the dose ladder.
3. If your level is already in range and you are under 75, don't expect a top-up to lower your risk of death. Neither D-Health nor VITAL found that it does. The 2024 Endocrine Society guideline does suggest extra vitamin D from age 75, because it may lower death risk.

Further reading

• Neale RE et al. The D-Health Trial: a randomised controlled trial of the effect of vitamin D on mortality. Lancet Diabetes & Endocrinology 2022.^[13]
• Thompson B et al. Vitamin D supplementation and major cardiovascular events: D-Health randomised controlled trial. BMJ 2023.^[14]
• Waterhouse M et al. The effect of monthly vitamin D supplementation on fractures: a tertiary outcome from the population-based, double-blind, randomised, placebo-controlled D-Health trial. Lancet Diabetes & Endocrinology 2023.^[15]
• Neale RE et al. The effect of vitamin D supplementation on cancer incidence in the randomised controlled D-Health Trial: Implications for policy and practice. J Steroid Biochem Mol Biol 2025.^[16]
• Kuznia S et al. Efficacy of vitamin D3 supplementation on cancer mortality: systematic review and individual patient data meta-analysis. Ageing Research Reviews 2023.^[17]