Associations of Outdoor Temperature, Bright Sunlight, and Cardiometabolic Traits in Two European Population-Based Cohorts

Seasonal variation in cold and light exposure may influence metabolic health. We assessed the associations of bright sunlight and outdoor temperature with measures of glucose and lipid metabolism in two populations of middle-aged European subjects. Cross-sectional study. Two population-based European cohorts. Middle-aged nondiabetic subjects from the Oxford Biobank (OBB; N = 4327; mean age, 41.4 years) and the Netherlands Epidemiology of Obesity (NEO) study (N = 5899; mean age, 55.6 years). Data on outdoor bright sunlight and temperature collected from local weather stations. Insulin resistance and fasting lipid levels. Multivariable regression analyses were adjusted for age, sex, percentage body fat, season, and either outdoor temperature or bright sunlight. In the OBB cohort, increased bright sunlight exposure was associated with lower fasting insulin [−1.27% (95% CI, −2.09 to −0.47%) per extra hour of bright sunlight], lower homeostatic model assessment for insulin resistance (−1.36%; 95% CI, −2.23 to −0.50), lower homeostatic model assessment for β-cell function (−0.80%; 95% CI, −1.31 to −0.30), and lower triglyceride (−1.28%; 95% CI, −2.07 to −0.50) levels. In the NEO cohort generally unidirectional but weaker associations were observed. No associations between outdoor temperature and measures of glucose or lipid metabolism were detected following adjustment for bright sunlight. Bright sunlight, but not outdoor temperature, might be associated with increased insulin sensitivity and lower triglyceride levels.