A common recommendation is 600–800 IU (15–20 mcg). Many experts suggest 1,000–2,000 IU during winter months.

Should I test 25(OH)D?

An optimal range is generally 30–50 ng/mL. Below 20 ng/mL is considered deficient.

D3 (cholecalciferol) raises and maintains levels better than D2.

Vitamin D3: Immune Support, Bones, and Muscles

During the fall and winter months across much of the US, sunlight is often too weak to produce enough vitamin D in the skin. As a result, a large share of adults have suboptimal levels for much of the year.