Does sunlight act as a prophylactic against diabetes?

Author(s): Karl J. Neeser

Today, several studies show a relationship between type-2 diabetes mellitus (DM) and sun exposure or UVB exposure. Blood-sugar levels were lower during the summer1 or exposure to UVB sun lamps demonstrated increased insulin secretion.2 A direct and significant association between low vitamin D levels (a surrogate measure for low sun exposure) and increased risk of type-2 diabetes has also been found.3,4 A meta-analysis produced moderate evidence that recreational sun exposure is associated with a reduced risk of type-2 diabetes.5 Researchers observed that although higher 25(OH)D levels were consistently associated with a lower risk of diabetes, supplementing 25(OH)D had shown no such effects. They hypothesized that sun exposure could have influences not related to vitamin D, and such seems to have been the case. Another of the more important investigations showed that women who had frequent sun exposure habits had a 30% reduced risk of type-2 diabetes.6 A number of results to date generally satisfy Hill's criteria for causality regarding vitamin D and incidence of pancreatic diseases like diabetes or cancer