How do you get enough vitamin D in winter?

Vitamin D is unusual: your body can make it from sunlight. But that depends on UVB rays reaching your skin at a strong enough angle — and in winter, at much of the latitude of the United States, they don't.

Why latitude matters

A classic 1988 study measured vitamin D production in skin samples exposed to sunlight. In Boston (about 42°N), there was essentially no production from November through February; in Edmonton, Canada (about 52°N), the "vitamin D winter" stretched from October through March. Farther south, in Los Angeles and Puerto Rico, production continued through winter.

As a rough rule, the farther north you live, the longer your vitamin D winter. Our location guides estimate the window for all 50 states and 100 cities.

How much vitamin D do you need?

According to the NIH Office of Dietary Supplements, the Recommended Dietary Allowance is:

Winter strategies that work

• Eat vitamin D foods: fatty fish two or more times a week, fortified milk or plant milk, eggs and UV-exposed mushrooms.
• Get outside anyway: midday winter light won't make much vitamin D at high latitudes, but it still helps your mood and body clock.
• Test, don't guess: a 25-hydroxyvitamin D blood test shows your actual status — it's part of the baseline labs we cover in preventative wellness. Your clinician can advise on supplements based on the result, your diet and any medications.

Who's at higher risk of low vitamin D?

Older adults (see our healthy aging guide), people with darker skin, people who spend little time outdoors, and people with conditions affecting fat absorption are more likely to run low — another reason testing beats assumptions.