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Vitamin D

Also known as: Vitamin D3, Cholecalciferol

A vitamin made in the skin from sunlight. Deficiency is common in winter, at higher latitudes, and in people with darker skin.

Common forms: D3 softgels · D3 drops · D2 (ergocalciferol)

Draft summary, not yet reviewed by a qualified health professional · Last updated 2026-11-03

Talk to a healthcare professional first

This information is for education only and is not medical advice, diagnosis, or treatment. Supplements can interact with medications and health conditions. Check with your doctor or pharmacist before starting anything, especially if you take medication, are pregnant or breastfeeding, or have a health condition. These statements have not been evaluated by the FDA; supplements are not intended to diagnose, treat, cure, or prevent any disease.

What the evidence says

Colds & immune support

CLimited evidence

An earlier meta-analysis suggested vitamin D slightly reduced respiratory infections, but the 2025 update (61,000+ participants) found the effect was no longer statistically significant, with no clear benefit by baseline vitamin D level or dosing schedule.

Dose used in studies
400–2,000 IU/day (daily dosing)
Time to effect
Weeks to months
Most relevant for
Correcting a confirmed deficiency is worthwhile for overall health
Studies (2)

Bone health

CLimited evidence

Vitamin D alone did not reduce fractures in community-dwelling adults; combined calcium + vitamin D showed a small reduction in some analyses, mainly in older or institutionalized people.

Dose used in studies
800–1,000 IU/day, usually with calcium
Time to effect
Months to years
Most relevant for
Older adults at fracture risk, together with calcium
Studies (3)

Safety

Common side effects

  • Rare at normal doses

Avoid or ask your doctor first if

  • You have high blood calcium, sarcoidosis, or recurrent kidney stones

Pregnancy & breastfeeding

Likely safe at normal dietary doses — confirm with your provider.

Upper limit

4,000 IU/day (100 mcg) for adults

Medication interactions

  • moderateBlood pressure medications: With thiazide diuretics, high doses may raise blood calcium too much.

This list covers common medication classes only and is not exhaustive.

Buying tips

Look for third-party testing seals (USP Verified, NSF Certified, or Informed Choice) and match the form and dose used in studies.

Where to buy (affiliate)

Further reading