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Vitamin D

Vitamin D is the fat-soluble hormone-vitamin that regulates calcium absorption, bone mineralisation, and multiple immune pathways. The IOM RDA is 600 IU/day for adults 19–70 and 800 IU/day for 71+; the Endocrine Society recommends 1,500–2,000 IU/day for deficiency correction. Blood 25(OH)D is the accepted status marker.

Salmon fillet, egg yolks, and a small supplement bottle on a stone board.
Salmon fillet, egg yolks, and a small supplement bottle on a stone board.

What vitamin D actually is

Vitamin D is not really a vitamin — it is the precursor of a steroid hormone (calcitriol, 1,25-dihydroxyvitamin D₃) that binds a nuclear receptor and regulates hundreds of genes, most centrally those governing intestinal calcium and phosphate absorption and osteoclast activity in bone remodelling. Two forms enter the body: D₂ (ergocalciferol) from plant sources and UV-irradiated yeast, and D₃ (cholecalciferol) from animal sources and the skin's conversion of 7-dehydrocholesterol by UVB radiation.

Intake references

  • IOM RDA: 600 IU/day (15 μg) for adults 19–70; 800 IU/day (20 μg) for 71+.
  • Endocrine Society: 1,500–2,000 IU/day for adults at risk of deficiency.
  • EFSA AI: 15 μg/day for adults.
  • UL (IOM): 4,000 IU/day (100 μg) for adults.

Sources

  • Oily fish: salmon (~450–600 IU per 3.5 oz), mackerel (~370 IU), sardines (~200 IU).
  • Fortified foods: most US and Canadian milk (~120 IU/cup), fortified plant milks and orange juice, some breakfast cereals.
  • Egg yolks: ~40 IU each.
  • UV-treated mushrooms: up to 400 IU per 3.5 oz.
  • Cutaneous synthesis: ~1,000–3,000 IU from 10–20 minutes of midday summer sun at mid-latitudes, skin-type dependent.

What the evidence supports

Bone and muscle outcomes in adults with baseline 25(OH)D below 20 ng/mL respond to supplementation (Bischoff-Ferrari, NEJM 2012;367:40–49; Weaver, Osteoporosis International 2016;27:367–376). The evidence weakens progressively for:

  • Cardiovascular disease: VITAL (Manson 2019, n=25,871, 5-year follow-up) reported no reduction in major CV events at 2,000 IU/day.
  • Cancer incidence: VITAL secondary analysis reported no reduction in incidence; a modest reduction in cancer mortality reached borderline significance.
  • Respiratory infection: Jolliffe 2021 IPD meta-analysis found a small reduction (RR 0.92) with daily/weekly dosing.
  • All-cause mortality: Chowdhury (BMJ 2014;348:g1903) meta-analysis reported an 11% reduction with supplementation in older adults.

How NakedCalorie treats vitamin D

Vitamin D is shown per serving in μg (or IU) on the nutrient panel, where declared. Fortified vitamin D in a Group 4 formulation does not raise the food-quality score above what the NOVA group earns. See calcium for the co-nutrient in bone health and dietary fats for the absorption pathway.

Frequently asked questions

How much vitamin D do adults need?
The IOM RDA is 600 IU/day (15 μg) for adults 19–70 and 800 IU/day (20 μg) for adults 71+, set to keep serum 25(OH)D above 20 ng/mL. The Endocrine Society recommends 1,500–2,000 IU/day (37.5–50 μg) for correcting documented deficiency, targeting >30 ng/mL.
What blood level counts as deficient?
The IOM threshold is 20 ng/mL (50 nmol/L) — below this, bone health starts to suffer. The Endocrine Society uses 30 ng/mL (75 nmol/L). Neither cutoff is disputed for skeletal outcomes; both are conservative for extra-skeletal endpoints where the RCT evidence is thinner.
Does the sun really produce enough?
Ten to twenty minutes of midday summer sun to face and forearms at temperate latitudes yields ~1,000–3,000 IU depending on skin type — but only in months when the UVB index rises above ~3, which excludes autumn and winter in most of Europe, Canada, and the northern US. Skin ageing and cancer risk mean sun exposure is a poor lever for many adults.
Does vitamin D prevent respiratory infections?
Individual-participant-data meta-analysis (Jolliffe, Lancet Diabetes & Endocrinology 2021;9:276–292) of 46 RCTs (48,488 participants) found a small (RR 0.92) reduction in acute respiratory infections with daily or weekly (not bolus) supplementation. VITAL (Manson, NEJM 2019;380:33–44) found no reduction in cardiovascular events or cancer at 2,000 IU/day over 5 years in generally sufficient participants.
Can you overdose from food?
Essentially not from food. Toxicity is a supplement issue, generally requiring >10,000 IU/day for months and blood 25(OH)D >150 ng/mL. The IOM UL is 4,000 IU/day for adults.

Written by NakedCalorie editorial team.

Medically reviewed by Pending registered dietitian review — last reviewed July 15, 2026.

Educational information only, based on peer-reviewed literature and regulatory sources. Not medical advice.

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