Evidence grade: B
Correcting a deficiency matters for bone and muscle health. In VITAL, a large trial of about 25,000 adults, extra vitamin D showed little added benefit for most major outcomes in people who were not low.
What it is
A fat-soluble vitamin your skin makes from sunlight. It also comes from fatty fish, eggs and fortified foods. It helps you absorb calcium.
What people claim
- Stronger bones
- Better muscle function
- Immune support
- Long-term health support (large trials found little benefit for people who were not low)
Doses used in studies
Adult recommended intakes (not study doses) are about 600–800 IU (15–20 mcg) a day. VITAL tested 2,000 IU a day. A blood test (25-hydroxyvitamin D) shows whether you are low.
These are amounts researchers tested, not a recommendation for you.
Who should be cautious
- Very high doses can raise blood calcium; the adult upper limit is 4,000 IU a day unless a doctor says otherwise
- People with kidney stones, sarcoidosis or high calcium
- Interacts with some medicines, including steroids and some diuretics
- Pregnant or nursing people: ask a doctor first, as safety data is limited
- Under 18: talk to a doctor or parent before using any supplement
Holistic and Eastern context
Many traditions value morning sun. Brief, sensible sun exposure is the natural source, balanced against skin-cancer risk.
Sources
- Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL) Manson et al., N Engl J Med, 2019
- Vitamin D fact sheet for health professionals NIH Office of Dietary Supplements
← All supplements · Laws & Research
Education only, not medical advice. Supplements are not reviewed by the FDA for safety or effectiveness before sale, and nothing here is meant to diagnose, treat, cure or prevent any condition. Talk to your doctor or pharmacist before starting any supplement, especially if you are pregnant, nursing, take medication or have a health condition.