Sun Exposure and Type 2 Diabetes Mellitus: A Prospective Follow-up Cohort Study from Southern Sweden.

Background/aim: An inverse association exists between type 2 diabetes mellitus (T2DM) and both plasma vitamin D levels and sun exposure, but vitamin D supplementation does not reduce the incidence. We sought to assess whether there is a dose-dependency in the association between sun exposure and T2DM.

Patients and methods: The melanoma in Southern Sweden (MISS) cohort is comprised of one thousand women without cancer from age groups between 25 and 64, drawn from the Southern Swedish Population Registry of 1990 by random selection. At the inception of the study, 74% of those women responded in writing to an inquiry (n=29,518) and provided detailed information on their sun exposure habits, age, exercise, education, and age at menarche. At the 11-year follow-up, 24,098 responses were received. We analyzed the data using logistic regression analysis with T2DM as a dependent variable and other as independent.

Results: We found a dose-dependent inverse relationship between degree of sun exposure and incidence of T2DM. Compared to women with the greatest sun exposure habits, those with moderate and low sun exposure had an odds ratio (OR) of 1.47, [95% confidence interval (CI)=1.2-1.8] and 2.47, (95% CI=1.8-3.4) for T2DM, respectively. In addition, the OR for T2DM was higher in women with normal BMI than in overweight women [3.72 (95% CI=1.8-7.9) vs. 1.90, (95% CI=1.3-2.7)].

Conclusion: A strong inverse dose-dependent association between sun exposure and T2DM indicated that an inverse causal relationship may exist between sun exposure and the incidence of T2DM, possibly via nitric oxide.