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The vitamin D window

Your skin makes vitamin D when it is hit by UVB, and UVB only reaches the ground in useful amounts when the sun is fairly high in the sky — roughly when the UV index is 3 or more. That simple fact drives when, and whether, you can make vitamin D from the sun.

General sun-safety information, not medical advice. Burn times vary enormously with skin, the UV index, altitude, reflection off snow or water, and some medicines — when in doubt, cover up. Any new, changing or unusual mole or spot should be checked by a doctor.

The "vitamin D winter"

At high latitudes — including the Baltic and Nordic countries and much of northern Europe — the winter sun sits too low for months for your skin to make meaningful vitamin D, no matter how long you stay out. This "vitamin D winter" runs roughly from October to March. In that window, vitamin D has to come from diet (oily fish, eggs, fortified foods) or a supplement, which is why many northern health authorities recommend one over winter.

Skin type and time change the dose

In the sunnier half of the year, short exposures around the middle of the day make vitamin D efficiently. How long you need depends on your skin: fairer skin makes it faster, darker skin needs considerably longer. The catch is that fair skin also burns quickly, so the goal is brief, regular exposure that stops well short of pinkness — never a burn in the name of vitamin D.

Related

Source: WHO Global Solar UV Index and general dermatology and public-health guidance. General information, not medical advice. · checked 2026-09-04

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