The artificial glow of a lightbulb or smartphone at night might disrupt the body’s natural circadian rhythm, according to new research suggesting a connection between nighttime light exposure and an increased risk of developing type 2 diabetes.
Conducted with nearly 85,000 participants aged 40 to 69, the study involved monitoring light exposure levels through wrist-worn devices over a week. Part of the extensive UK Biobank experiment, the health outcomes of these individuals were tracked for up to nine years. It was found that 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 monitoring period.
While the study does not establish a direct cause-and-effect relationship, it indicates a dose-dependent link between nighttime light exposure and the risk of developing metabolic disorders, strengthening the association between the two.
Participants in the highest 10 percent of nighttime light exposure had a 67 percent greater risk of developing type 2 diabetes compared to those in the lowest 50 percent.
Previous research indicates that artificial light at night, from sources such as reading lamps, smartphones, or TVs, can hinder sleep onset. However, this study’s findings remained consistent even after adjusting for sleep patterns and duration, suggesting other mechanisms might be influencing the results.
The study also accounted for variables such as sex, genetic diabetes risk, diet, physical activity, daylight exposure, smoking, and alcohol use, none of which altered 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,” concluded the study authors, led by researchers at Monash University in Australia.
Prior observational studies have similarly linked nighttime artificial light to insulin resistance, but these did not measure indoor light sources as precisely or for as extended a period.
Emerging evidence from animal and human studies suggests that artificial light exposure can disrupt circadian rhythms, leading to reduced glucose tolerance, altered insulin secretion, and weight gain—all of which are associated with a higher risk of metabolic disorders like type 2 diabetes.
However, the study had limitations, including the inability to account for meal times, which affect circadian rhythms and glucose tolerance. Socioeconomic factors were also considered at a regional rather than individual level, and only older adults were included in the study.
Individual responses to light vary significantly, with some studies indicating that the intensity of light needed to suppress melatonin production, crucial for regulating circadian rhythm, ranges widely from 6 to 350 lux.
Despite these limitations, previous experiments suggest that melatonin disruption and circadian rhythm disturbances can lead to decreased insulin secretion by the pancreas, potentially contributing to diabetes development.
More rigorous studies are necessary to fully understand how nighttime light exposure impacts circadian rhythms and, consequently, the body’s metabolic health.
Some research suggests that a weekend of camping without artificial light can help reset a person’s circadian rhythm—perhaps a simple, nature-based intervention worth considering.
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