02 July 2024, Exposure to artificial light at night, such as from a lightbulb or smartphone, may disrupt the body’s circadian rhythm and increase the risk of developing type 2 diabetes, a new study suggests.
The research, conducted among nearly 85,000 people aged 40 to 69, tracked participants’ exposure to different levels of light using wrist-worn devices over one week. As part of the UK Biobank experiment, the health of the cohort was monitored for up to nine years. Those who developed type 2 diabetes were more likely to have been exposed to light between 12:30 am and 6:00 am during the study period.
The results do not establish a direct cause-and-effect relationship but show a dose-dependent link between nighttime light exposure and the risk of a metabolic disorder. Participants in the top 10 percent for light exposure at night had up to a 67 percent higher risk of developing type 2 diabetes compared to those in the bottom 50th percentile.
Artificial light at night, whether from a reading lamp or a smartphone, can make it harder to fall asleep. However, the study found that the association between light exposure and diabetes risk persisted even after accounting for sleep patterns and duration, suggesting another underlying mechanism.
Other factors such as sex, genetic risk for diabetes, diet, physical activity, daylight exposure, smoking, and alcohol use did not alter the results.
“Advising people to avoid night light is a simple and cost-effective recommendation that may ease the global health burden of type 2 diabetes,” conclude the study’s authors, led by researchers at Monash University in Australia.
Previous observational studies have linked artificial light at night to insulin resistance, but those studies did not measure indoor light sources as closely or for as long.
Emerging evidence suggests that exposure to artificial light can disrupt circadian rhythms, leading to reduced glucose tolerance, altered insulin secretion, and weight gain all tied to an increased risk of metabolic disorders like type 2 diabetes.
One limitation of the study is that meal times, which can affect circadian rhythms and glucose tolerance, were not accounted for. Additionally, some socioeconomic factors were measured at a regional rather than individual level, and only older adults were considered.
Individual responses to light vary, with some studies suggesting that the intensity of light needed to suppress melatonin production can range from 6 to 350 lux. Disrupted melatonin production and circadian rhythms can reduce insulin secretion from the pancreas, potentially contributing to diabetes development.
More rigorous studies are needed to understand how nighttime light impacts circadian rhythms and metabolic health. Some research suggests that a weekend of camping without artificial light can help reset a person’s circadian rhythm, a potential recommendation for maintaining metabolic health.
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