How much sunlight do you need in order to produce enough Vitamin D?

16 June 2021

In a simulation of ultraviolet (UV) light, researchers calculated the amount of vitamin D produced when exposing your skin to the sun under various conditions of UV radiation.

More precisely, they determined the ultraviolet (UV) B (UVB) irradiance and the exposure time needed to achieve effective serum vitamin D3 doses at various periods of the year and at different times of the day, in Miami, FL, and in Boston, MA. These two cities have very different latitudes, Boston being in the northern east of the USA with a latitude of 42.3°N, and Miami being in the south of the USA at a latitude of 25.8°N. The results of this simulation reveal the amount of vitamin D produced by exposing 25.5% of the skin area (which is equivalent to exposing your face, neck, hands and arms), and that is equivalent to 1000 IU (international units).

For a skin type 1 (light white skin), the results show that approximately 10 min of sun exposure in enough in January in Miami at midday to synthetize 1000 IU of Vitamin D, but 40 min is needed if you live in Boston. Quite a difference! Moreover, bear in mind that a dose of 1000 IU is not that much Vitamin D. Many medical doctors and experts recommend much higher amounts of Vitamin D to prevent deficiency.

If you have a darker skin (e.g. type 5, see my previous post from April 28 to learn about skin types), you will need a lot more exposure time in order to produce the same amount of Vitamin D under the same conditions as above. If you live in Miami, you will need 2 hours of sun exposure, and if you live in Boston… well the simulations show that you won’t be able to produce that much Vitamin D no matter how long you expose your skin! Indeed, studies have shown that if you have a dark skin the amount of Vitamin D produced can be dramatically reduced by as much as 90% or more compared to a light/fair skin type!

Reference

Journal of the American Academy of Dermatology

Volume 62, Issue 6, June 2010, Pages 929.e1-929.e9

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