Vitamin D in the United States
The US has two major sets of vitamin D recommendations — from the Institute of Medicine (now NASEM) and from the Endocrine Society — which don't fully agree. Milk fortification since the 1930s largely eliminated childhood rickets. Adult vitamin D adequacy varies dramatically by latitude, ethnicity, and lifestyle.
IOM vs Endocrine Society
- IOM 2011 (still official reference): RDA 600 IU/day ages 1–70, 800 IU age 71+. Target 25(OH)D ≥ 20 ng/mL sufficient. Upper limit 4,000 IU/day.
- Endocrine Society 2011: 1,500–2,000 IU/day for adults at risk. Target 25(OH)D ≥ 30 ng/mL. Upper limit up to 10,000 IU/day for correction.
- IOM designed for population bone health; Endocrine Society for individual clinical management. Both defensible for their purposes.
NHANES data
National Health and Nutrition Examination Survey (NHANES) has tracked US 25(OH)D since 1988. Key findings:
- ~24% of US adults have 25(OH)D < 20 ng/mL (IOM deficient).
- ~40% have < 30 ng/mL (Endocrine Society insufficient).
- Highest deficiency rates: non-Hispanic Black adults (~76% < 30 ng/mL), Hispanic (~54%), non-Hispanic White (~29%).
- Winter deficiency rates higher across all groups.
State-by-state seasonal patterns
Above the "37° line" (roughly from Kansas City through Louisville to Washington DC), meaningful vitamin D winter runs November through March. Below that line (from Los Angeles through Dallas to Atlanta), vitamin D synthesis is possible year-round in fair-skinned adults. See our latitude page for city-by-city detail.
Milk fortification
Since the 1930s, US fluid milk has been fortified with vitamin D at 100 IU/cup. Combined with butter/margarine fortification and (later) breakfast cereal fortification, this ended endemic US childhood rickets. Adult supplementation levels from fortified foods remain modest (typically 100–300 IU/day dietary contribution) — not enough to prevent adult deficiency without supplementation.
Testing 25(OH)D in the US
Widely available through primary care, LabCorp, Quest, and direct-to-consumer services. Insurance coverage varies with diagnosis code. Out-of-pocket cost $30–100. Direct-to-consumer options (Everlywell, LetsGetChecked, Rupa Health, Function Health) increasingly popular.
Practical US dosing
- Standard adult maintenance: 1,000–2,000 IU/day cholecalciferol year-round.
- Above 37° latitude, winter: at least the 1,000–2,000 IU/day; testing recommended if deficiency history.
- Non-Hispanic Black adults, veiled women, housebound elderly: year-round supplementation regardless of location.
- Corrective dosing per Endocrine Society: 50,000 IU/week × 8 weeks if deficient, then maintenance.