Healthy, middle-aged adults exposed to more bright sunlight in the 7 days before providing a blood sample had lower levels of markers indicating risk for insulin resistance and dyslipidemia vs. adults exposed to less sunlight, according to findings published in The Journal of Clinical Endocrinology & Metabolism.
“Spending more time outdoors in the sun might be associated with health benefits,” Constantinos Christodoulides, MD, PhD, a university research lecturer and honorary consultant in diabetes and endocrinology at the Oxford Centre for Diabetes, Endocrinology and Metabolism at the University of Oxford, United Kingdom, told Endocrine Today. “Increased bright sunlight exposure may be associated with a reduced risk for type 2 diabetes and heart disease by lowering blood insulin and lipid levels.”
Christodoulides and colleagues analyzed data from middle-aged adults without diabetes using data from the Oxford Biobank, a population-based cohort of randomly selected healthy participants from Oxfordshire, United Kingdom (n = 4,327; mean age, 41 years), and the Netherlands Epidemiology of Obesity study (n = 5,899; mean age, 56 years), a population-based, prospective cohort study of adults without diabetes living in the greater area of Leiden, the Netherlands. Participants in both cohorts completed baseline assessments, including body composition measurements via DXA and providing fasting blood samples. Data on mean outdoor temperature and hours of bright sunlight (defined as global radiation 120 W/m²) were collected from local weather stations. Researchers calculated the mean outdoor temperature and bright sunlight duration during a 7-day and 30-day period before date of blood sampling, and used linear regression analyses to assess associations between mean bright sunlight and temperature with measures of insulin resistance and dyslipidemia.
Researchers noted that the mean outdoor temperature was similar in the two geographic regions, although the median number of hours of bright sunlight duration was lower in the Oxfordshire area vs. the Leiden area (mean, 3.8 hours vs. 5 hours).
In the Oxfordshire cohort, researchers found that each additional 1-hour increase in bright sunlight during the 7 days before blood sampling was associated with a –1.05% decrease in insulin resistance (95% CI, –1.65 to –0.45) and a –0.54% improvement in beta-cell function (95% CI, –0.89 to –0.19). Both associations were driven by a mean –0.92% decrease in fasting insulin level per 1-hour increase of bright sunlight (95% CI, –1.48 to –0.36), according to researchers.
Longer exposure to bright sunlight in the 7 days before blood sampling was also associated with lower LDL cholesterol (mean, –0.36%; 95% CI, –0.66 to –0.07) and lower triglyceride levels (mean, –0.57%; 95% CI, –1.12 to –0.03); however, the association for LDL cholesterol no longer persisted after adjustment for season and mean outdoor temperature.
In the Leiden area cohort, researchers observed similar associations between bright sunlight and glucose and lipid metabolism, but with smaller effect sizes, they wrote.
There were no associations between outdoor temperature and glucose and lipid metabolism after adjustment for mean bright sunlight, according to researchers.
“Replication of our findings in other large cohorts of healthy subjects and patients with type 2 diabetes and heart disease, followed by clinical trials assessing the role of light therapy as an adjuvant therapy for these disorders, is needed,” Christodoulides said. “We would also need to understand the underlying biological mechanisms driving the beneficial effects of bright sunlight on blood insulin and lipid levels through biomedical research if these are confirmed.” – by Regina Schaffer
For more information:
Constantinos Christodoulides, MD, PhD, can be reached at the Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, OX3 7LE, Oxford, United Kingdom; E-mail: firstname.lastname@example.org.
Disclosures: The authors report no relevant financial disclosures.