Vitamin D (if deficient)
Last reviewed 25 August 2026 · Evidence-graded review — see Methodology
Vitamin D supplements are worth taking if you are deficient, and largely unnecessary if you are not. The largest randomised trial ever run on them found no protection against cancer or heart disease in generally healthy, non-deficient adults. Correcting a documented deficiency is ordinary good care; swallowing sunshine pills speculatively is neither.
The VITAL trial randomised nearly 26,000 US adults to 2,000 IU a day of vitamin D or placebo and found no significant reduction in invasive cancer or major cardiovascular events over about five years. Bone-fracture results in similar trials are equally unimpressive in replete populations. Supplementation in genuine deficiency restores normal physiology, which is a different question and a defensible one.
Doing it: If you rarely get midday sun or have darker skin living far from the equator, ask for a 25(OH)D test before buying anything; Singapore residents are often surprised either way. If deficient, take the replacement dose your doctor specifies and recheck once. Otherwise, sunlight and food cover most people.
Who it suits: People with documented deficiency, limited sun exposure, or malabsorption. Everyone else is buying expensive urine within measurement error.
Sources
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