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Also: vitamin D · vitamin D-3 · the sunshine vitamin
Four separate measurements, never averaged. Independent evidence counts only studies with no sponsor attached. Methodology version v2.0-2026-10 · how we grade evidence
Claimed to prevent cancer and cardiovascular disease, prevent fractures and falls, prevent type 2 diabetes, support immunity and assist weight loss. Correcting a deficiency and supplementing someone already replete are two different interventions, and almost all of the evidence base speaks to the second. NIH ODS thresholds are deficiency below 30 nmol/L (12 ng/mL), inadequacy from 30 to under 50 nmol/L, and sufficiency for most people at or above 50 nmol/L (20 ng/mL). Deficiency causes rickets and osteomalacia and repletion cures them; that much is settled.
In replete populations the extraskeletal claims did not survive randomisation. VITAL (n=25,871) was null for invasive cancer, major cardiovascular events and all-cause death; its ancillary fracture study was null for total, nonvertebral and hip fractures and found no difference by baseline 25(OH)D level; D-Health (n=21,315, placebo arm already at 77 nmol/L) was null for all-cause mortality and showed a nominal signal towards higher cancer mortality on exploratory analysis; D2d (n=2,423, baseline 27.7 ng/mL) missed significance for diabetes prevention at a dose sitting at the upper intake level.
ODS states supplementation offers little benefit for glucose control or diabetes prevention particularly in replete individuals, that across cardiovascular trials it did not reduce risk even among participants with low status, and that the research does not support using it to promote weight loss, with a meta-analysis finding no effect on body weight or fat mass absent calorie restriction. A post hoc D2d subgroup with baseline 25(OH)D below 30 nmol/L showed 62% lower diabetes incidence — hypothesis-generating, not a trial finding.
At a glance
Hydroxylated to 25(OH)D and then to 1,25(OH)2D, which acts through the nuclear vitamin D receptor to regulate intestinal calcium and phosphate absorption and bone mineralisation. The receptor is expressed in many non-skeletal tissues, which is what generated the cancer, cardiovascular and antidiabetic hypotheses. The calcium–phosphate and bone-mineralisation mechanism is confirmed in humans. **The extraskeletal mechanisms are not**: the proposed anti-cancer, cardioprotective and antidiabetic pathways failed when tested in large randomised trials, so a receptor being present in a tissue is not evidence that supplementation changes anything in it.
Dated determinations, each flagged for whether it is final and whether it covers safety only. A safety review is not an efficacy finding, and most reporting in this category conflates the two.
Dual status: a supplement ingredient and a permitted fortificant in conventional foods.
Food and Nutrition Board limit, recorded in the NIH ODS fact sheet last modified 13 October 2026, which also advises avoiding serum 25(OH)D above roughly 125–150 nmol/L (50–60 ng/mL). Harms of excess are hypercalcaemia and hypercalciuria, typically above about 375 nmol/L, with nausea, vomiting, muscle weakness, pain, dehydration, thirst and kidney stones, and in extreme cases renal failure, soft-tissue calcification, arrhythmias and death. ODS also reports that serum levels of about 75–120 nmol/L have been linked to higher all-cause mortality, certain cancers, cardiovascular events and falls and fractures in older adults, and that combining high calcium with moderate vitamin D raised kidney-stone risk by 17% in one trial of postmenopausal women. Adverse events did not differ from placebo in VITAL, D-Health or D2d. D2d tested a dose sitting at this upper limit and still found no significant diabetes prevention.
In the Annex of authorised claims under Regulation (EU) 432/2012. Each requires only that the food be at least a "source of" vitamin D, with no daily amount specified. Note the asymmetry this creates: the European Union authorises bone and immune claims while four large independent RCTs found no fracture or mortality benefit in replete adults, and the VITAL fracture study found no difference by baseline 25(OH)D level.
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