YahGarden

Supplements

Vitamin D

A nutrient made in sunlit skin and found in a few foods and fortified products. It helps the body absorb calcium for bones; trials have returned clear negative results for several uses it is sold for.

Traditional use

A nutrient, not a herbal tradition. Sources: fatty fish and fish liver oils, fortified milk, plant milks, and cereals, small amounts in egg yolks, liver, cheese, and some mushrooms, and bare skin in sunlight.

What studies show

  • Established

    Bone health: long-term shortage of vitamin D and calcium makes bones fragile, and deficiency causes rickets and osteomalacia. Supplements with calcium slightly increase bone strength in older adults; whether that reduces falls or fractures is unclear.

  • Limited

    Sleep: a 2022 review of 19 studies suggested it may improve sleep quality; its effect on sleep quantity and sleep disorders is not clear.

  • Limited

    Cancer: it does not seem to lower breast, colon, rectal, or lung cancer risk; prostate is unclear; very high blood levels may raise pancreatic cancer risk. Trials suggest supplements might slightly reduce cancer deaths.

  • Established

    Heart disease: overall, trials find supplements do not reduce the risk of developing heart disease or dying from it, even with low levels; blood pressure and cholesterol studies are mixed.

  • Established

    Depression, type 2 diabetes, and weight: trials show supplements do not ease depression, do not improve blood sugar, insulin resistance, or hemoglobin A1c, do not stop most prediabetes progressing, and do not aid weight loss.

  • Established

    Multiple sclerosis: in people with MS, trials show supplements do not keep symptoms from worsening or returning. Low levels are linked to higher MS risk, but whether supplements change that risk is unstudied.

Be careful of

Cautions

  • AmountToo much is harmful: nausea, vomiting, weakness, confusion, dehydration, kidney stones, and at extreme levels kidney failure, irregular heartbeat, and death; it almost always comes from supplements, never sunshine. The daily upper limit from all sources is 100 mcg (4,000 IU) for adults, less for children, unless a provider prescribes more to correct a deficiency.
  • InteractionOrlistat reduces vitamin D absorption; statins may work less well with high-dose vitamin D; steroids such as prednisone lower vitamin D levels; thiazide diuretics plus vitamin D can push blood calcium too high.
  • ConditionBreastfed infants, older adults, people with little sun or dark skin, people with fat-absorption conditions such as Crohn's or celiac disease, and people with obesity or past gastric bypass more often run short; a blood test tells.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or have a medical condition.

Sources

  1. Vitamin D - Consumer (opens in a new tab) · NIH ODS · read September 15, 2026
  2. Sleep Disorders and Complementary Health Approaches: Usefulness and Safety (opens in a new tab) · NCCIH · read September 15, 2026

Reviewed September 15, 2026.