Context

Seasonal variation in cold and light exposure may influence metabolic health.

Objective

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.

Design

Cross-sectional study.

Setting

Two population-based European cohorts.

Participants

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).

Interventions

Data on outdoor bright sunlight and temperature collected from local weather stations.

Main outcome measures

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.

Results

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.

Conclusions

Bright sunlight, but not outdoor temperature, might be associated with increased insulin sensitivity and lower triglyceride levels.

Copyright © 2019 Endocrine Society.