How much sun do you really need for vitamin D? A balanced look at what the evidence supports — and what it doesn't.
Vitamin D is one of the most cited reasons people skip sunscreen. The reality is more nuanced: sun exposure does drive vitamin D synthesis, but it does not require sunburn-level doses, and supplementation is a safe alternative.
How sun makes vitamin D
UVB converts 7-dehydrocholesterol in the skin to previtamin D3, which the liver and kidneys later activate. Most people produce adequate vitamin D from short, casual sun exposure — roughly 5–15 minutes on arms and legs a few times a week, depending on latitude and skin type.
Sunscreen does not cause deficiency
Multiple studies (including a 2019 meta-analysis in the British Journal of Dermatology) show that real-world sunscreen use does not meaningfully reduce serum 25(OH)D levels. People apply far less than the lab-tested amount, and incidental UV is enough.
When to consider supplementation
If you live above 35° latitude in winter, work indoors, or have darker skin, ask your doctor about a daily 800–2000 IU vitamin D3 supplement. It avoids the cancer risk trade-off entirely.
Key takeaways
Casual incidental sun is enough for most people.
Sunscreen does not meaningfully cause vitamin D deficiency.
How to read this Vitamin D and the Sun: What's True, What's Hype page
The UV index is a measure of erythemal (skin-reddening) irradiance, where each whole point equals 25 mW/m² of UV energy reaching the surface. That is why burn-time estimates fall roughly by half when the index doubles.
UV strength on this page follows solar elevation, ozone thickness, cloud cover, altitude, and surface reflection. Snow can bounce back most of the UV that hits it, water and sand far less, but all of them add to the dose skin receives.
Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.
Cloud cover is not protection. Thin or broken cloud can still pass most incoming UV, and light cloud edges can briefly scatter more UV toward the ground than a clear sky.
Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.
UV scale reference
The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.
A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.
Keep exploring DermUV
These pages give more depth around vitamin d and the sun: what's true, what's hype, from UV-scale reference material to definitions and city forecasts.