Christina Szalinski July 11, 2024
Concerned about your patient’s type 2 diabetes risk? Along with the usual preventive strategies — like diet and exercise and, when appropriate, glucagon-like peptide 1 (GLP-1) agonists — there’s another simple, no-risk strategy that just might help: Turning off the light at night.
A study in The Lancet found that people who were exposed to the most light between 12:30 AM and 6 AM were 1.5 times more likely to develop diabetes than those who remained in darkness during that timeframe.
The study builds on growing evidence linking nighttime light exposure to type 2 diabetes risk. But unlike previous large studies that relied on satellite data of outdoor light levels (an indirect measure of light exposure), the recent study looked at personal light exposure — that is, light measured directly on individuals — as recorded by a wrist-worn sensor.
“Those previous studies likely underestimated the effect,” said study author Andrew Phillips, PhD, professor of sleep health at Flinders University in Adelaide, Australia, “since they did not capture indoor light environments.”
Using data from 85,000 participants from the UK Biobank, the recent study is the largest to date linking diabetes risk to personal light exposure at night.
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“This is really a phenomenal study,” said Courtney Peterson, PhD, a scientist at the University of Alabama at Birmingham’s Diabetes Research Center, who was not involved in the study. “This is the first large-scale study we have looking at people’s light exposure patterns and linking it to their long-term health.”
What the Study Showed
The participants wore the light sensors for a week, recording day and night light from all sources — whether from sunlight, lamps, streetlights, or digital screens. The researchers then tracked participants for 8 years.
“About half of the people that we looked at had very dim levels of light at night, so less than one lux — that basically means less than candlelight,” said Phillips. “They were the people who were protected against type 2 diabetes.”
Those exposed to more light at night — defined in the study as 12:30 AM-6 AM — had a higher risk for type 2 diabetes. The risk went up as a dose response, Phillips said: The brighter the light exposure, the higher the diabetes risk.
Participants in the top 10% of light exposure — who were exposed to about 48 lux , or the equivalent of relatively dim overhead lighting — were 1.5 times more likely to develop diabetes than those in the dark. That’s about the risk increase you’d get from having a family history of type 2 diabetes, the researchers said.
Even when they controlled for factors like socioeconomic status, smoking, diet, exercise, and shift work, “we still found there was this very strong relationship between light exposure and risk of type 2 diabetes,” said Phillips.
How Light at Night May Increase Diabetes Risk
The results are not entirely surprising, said endocrinologist Susanne Miedlich, MD, a professor at the University of Rochester Medical Center, Rochester, New York, who was not involved in the study.
Light at night can disrupt the circadian rhythm, or your body’s internal 24-hour cycle. And scientists have long known that circadian rhythm is important for all kinds of biologic processes, including how the body manages blood sugar.
One’s internal clock regulates food intake, sugar absorption, and the release of insulin. Dysregulation in the circadian rhythm is associated with insulin resistance, a precursor to type 2 diabetes.
Phillips speculated that the sleep hormone melatonin also plays a role.
“Melatonin does a lot of things, but one of the things that it does is it manages our glucose and our insulin responses,” Phillips said. “So if you’re chronically getting light exposure at night, that’s reducing a level of melatonin that, in the long term, could lead to poor metabolic outcomes.”
Previous studies have explored melatonin supplementation to help manage diabetes. “However, while melatonin clearly regulates circadian rhythms, its utility as a drug to prevent diabetes has not really panned out thus far,” Miedlich said.
Takeaways
Interventional studies are needed to confirm whether strategies like powering down screens, turning off lights, or using blackout curtains could reduce diabetes risk.
That said, “there’s no reason not to tell people to get healthy light exposure patterns and sleep, especially in the context of diabetes,” said Phillips.
Other known strategies for reducing diabetes risk include intensive lifestyle programs, which reduce risk by up to 58%, and GLP-1 agonists.
“Probably a GLP-1 agonist is going to be more effective,” Peterson said. “But this is still a fairly large effect without having to go through the expense of buying a GLP-1 or losing a lot of weight or making a big lifestyle change.”
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