As skin tans, it darkens to protect itself against harmful ultraviolet (UV) radiation, but the increasing pigment blocks vitamin D synthesis, limiting the skin's ability to produce more vitamin D, a new study from Brazil finds. The results will be presented in a poster Saturday, April 2, at ENDO 2016, the annual meeting of the Endocrine Society, in Boston.

Even people exposed to high levels of sunlight may be deficient in serum vitamin D because it is mainly induced by UV irradiation and synthesized in the .

"Our research showed that, in a large sample of individuals living in a tropical region located 8 degrees south of the equator with very high rates of sun exposure and extremely high UV irradiation, most people had serum vitamin D below 30 ng/ml (nanograms per milliliter), the cutoff for normal," said lead study author Francisco Bandeira, MD, PhD, associate professor of medicine and chief of the Division of Endocrinology and Diabetes at the University of Pernambuco Medical School in Recife, Brazil. "Our findings suggest that skin tanning, which is a natural protection against the harmful effects of UV irradiation, limits the progressive rise in serum vitamin D towards optimal concentrations."


The researchers evaluated each participant's Fitzpatrick skin phototype scale to estimate the response of different skin types to UV light. In general, higher Fitzpatrick scale scores indicate deeper color and tendency to tan rather than burn in the sun.


They measured everyone's serum vitamin D levels and compared them with their skin phototype and sun index scores.

