Recently published in the Journal of the American Academy of Dermatology, a study favours supplements over sun exposure for vitamin D.

Vitamin D can be synthesized by the body when the skin is exposed to UV rays. Since research indicates that vitamin D has benefits that go beyond bone health, science tries to find the best means to obtain sufficient vitamin D stores while avoiding the danger of UV rays, namely skin cancer.

Researchers form New York and Norway have united to determine what sun exposure would be necessary to match a supplement of 400 IU of vitamin D. A computer simulation was used to answer this burning issue, taking location into account: either Boston, a rather northern city, or Miami, in a tropical region.

In fact, the simulator showed that it would be hardly possible to simply synthesize vitamin D during winter in Boston. Hence, people living at similar latitudes or north, such as Canadians, should resort to supplement to get their daily vitamin D during winter days. During summer in Boston a sun exposure of 3-8 minutes would be required to obtain the same levels of vitamin D as a 400 IU supplement, provided that one quarter of the skin is exposed to the sun.

This simulation is generally feasible if daily outdoor time is spent with clothing that reveals a lot of skin surface. Researchers however prefer to recommend a vitamin D supplement due to the skin cancer risk associated with UV rays from the sun without proper sun protection such as sun cream.

In Miami, between 3 to 6 minutes of exposing one quarter of the skin surface would be sufficient to obtain vitamin D levels similar to what a 400 IU supplement would provide year round. This solution can be more realistic since in Florida, clothing is often leaving more skin exposed than in northern locations. Again due to the risk of skin cancer, researchers favoured supplements of vitamin D to obtain our daily fill.

References:

V. Terushkin, A. Bender, E.L. Psaty, O. Engelsen, S.Q. Wang, A.C. Halpern. Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes. Journal of the American Academy of Dermatology 2010; 62 (6): 929.e1-929.e9

Parker J, Hashmi O, Dutton D, Mavrodaris A, Stranges S, Kandala NB, Clarke A, Franco OH. Levels of vitamin D and cardiometabolic disorders: systematic review and meta-analysis. Maturitas 2010; 65(3): 225-236

Pittas AG, Lau J, Hu FB, Dawson-Hughes B. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. Journal of Clinical Endocrinology & Metabolism 2009; 92 (6): 2017-2029.