Safety · Supplement
Vitamin D: side effects, safety & interactions
Very safe in the ordinary range; toxicity (hypercalcemia) is real but requires sustained megadosing, typically well abov
- Overall grade
- Grade A
- Last revised
- 0
- graded outcomes
- 2
- references listed
Assembled by the app from other entries in this library. It adds no evidence of its own — follow the links to the entries it draws on.
The evidence in words
Safety profile
Very safe in the ordinary range; toxicity (hypercalcemia) is real but requires sustained megadosing, typically well above 10,000 IU/day for months. The classic mistake is high-dose D without magnesium (a required cofactor) or K2 (which directs calcium to bone rather than arteries).
Interactions to respect
No major interactions are on record for Vitamin D at typical doses, but tell your clinician about everything you take.
What Vitamin D is
Vitamin D is a fat-soluble secosteroid the skin makes from UVB sunlight and the gut absorbs from food or supplements. It is measured in blood as 25-hydroxyvitamin D (25(OH)D). Despite the name it behaves like a hormone: the active form, calcitriol, binds a nuclear receptor expressed in most tissues. Deficiency is common at higher latitudes, in darker skin, in the elderly, and in anyone who avoids the sun.
The honest bottom line
If you live away from the equator, get a 25(OH)D test. If you're low, 1,000–2,000 IU/day with a fatty meal, K2 and magnesium alongside, re-test at 12 weeks. If you're already replete, more does nothing — the megadose-prevents-everything story did not survive the big trials.
Related reading
Entries that share this one's tags or conditions.
- Vitamin DA steroid hormone precursor that most temperate-latitude adults run low on — worth correcting, oversold as a cure-all.Evidence grade A
- Vitamin D for Autoimmune diseaseEvidence grade C — VITAL hinted at a small reduction; not establishedEvidence grade C
- Vitamin D for Cancer / CVD prevention (replete adults)Evidence grade D — VITAL and others nullEvidence grade D
- Vitamin D for Correcting deficiency (25(OH)D)Evidence grade A — Dose-dependent, predictable riseEvidence grade A
Sources
As this entry records them: title, journal and year. None carries a DOI or PubMed id, so none is linked as a verified paper. Each link searches PubMed for the title; check that what you find is what the entry describes.
- 1.Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL) — N Engl J Med, 2019. Search PubMed (opens in a new tab)
- 2.Vitamin D and type 2 diabetes prevention (D2d) — N Engl J Med, 2019. Search PubMed (opens in a new tab)
Last revised . A grade is this entry's reading of the evidence, not medical advice.