In a massive study of 85,000 people, scientists at Flinders University have found that night-time exposure to light increases the risk of developing type 2 diabetes, independent of daytime activities.
“Light exposure at night can disrupt our circadian rhythms, leading to changes in insulin secretion and glucose metabolism,” said senior author Andrew Phillips, an associate professor from the College of Medicine and Public Health. “Changes in insulin secretion and glucose metabolism caused by disrupted circadian rhythms affect the body’s ability to regulate blood sugar levels, which can ultimately lead to the development of type 2 diabetes.”
Using UK Biobank data, 84,790 participants wearing wrist light sensors for a week between 2013 and 2016 were assessed nine years later. With 13 million hours of light-sensor data gathered, researchers found that there was up to 67% greater risk of developing diabetes later in life. The scientists also found that risk increased with the amount of time spent exposed to light, independent of daytime behaviors.
The data supports the hypothesis that light, which suppresses or shifts central circadian rhythms, putting them in an "abnormal phase", may also change how insulin is secreted and glucose metabolized.
"For example, disrupted circadian melatonin or glucocorticoid rhythms may exhibit elevated concentrations during waking hours, thereby reducing pancreatic insulin secretion, and promoting hepatic glucose production at times that coincide with food intake," they noted in the study. "Persistent circadian misalignment may lead to persistently elevated postprandial glucose levels, initiating the development of type 2 diabetes by increasing the size and inflammation of adipocytes, thereby promoting insulin resistance, and the secretion of inflammatory markers (e.g., interleukin-1β) that inhibit pancreatic beta-cell function."
While lifestyle and behaviors such as shift work, irregular sleeping patterns impact diabetes risk, the researchers accounted for these factors and still found that light exposure between 12.30 am and 6 am presented a significant health issue. The researchers, naturally, suggest limiting personal light exposure between these hours, in an effort to keep circadian rhythms on track, is for many an easy way to lower the risk of developing type 2 diabetes.
“The results showed that exposure to brighter light at night is associated with a higher risk of developing diabetes, with a dose-dependent relationship between light exposure and risk,” said Phillips. “Our findings suggest that reducing your light exposure at night and maintaining a dark environment may be an easy and cheap way to prevent or delay the development of diabetes."
The study was published in the journal The Lancet Regional Health – Europe.
Source: Flinders University
