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Light Exposure During Sleep May Increase Insulin Resistance

Healthy adults who slept with an overhead light on had significantly greater insulin resistance the next morning.


BALTIMORE—A single night of light exposure during sleep may acutely affect insulin resistance, according to research described at the 32nd Annual Meeting of the Associated Professional Sleep Societies. Studies have found that nighttime artificial light exposure affects circadian rhythms such as melatonin and sleep, and disturbances in these rhythms may affect cardiometabolic function.

To assess whether light exposure during sleep negatively affects cardiometabolic outcomes, possibly via disruptions to sleep architecture and melatonin profile, Ivy C. Mason, PhD, a research fellow at Harvard Medical School in Boston, and colleagues conducted a study in which they randomized 20 healthy adults ages 18 to 40 to different sleep conditions. The conditions were run in parallel for three days and two nights.

One group slept in the dark (ie, less than 3 lux) on the first night and in a lighted room (ie, with an overhead light of 100 lux) on the second night. The other group slept in the dark on both nights.

Participants had eight hours of sleep opportunity each night, starting at a habitual bedtime that was determined from one week of actigraphy with a sleep diary. On both nights, overnight polysomnography was performed and hourly blood samples were collected to measure melatonin.

Researchers performed oral glucose tolerance tests on both mornings and assessed changes from the first morning to the second morning. They compared the groups using repeated measures analysis of variance.

The dark–light group (n = 10; two males) had a mean age of 26.61 and a mean BMI of 23.25 kg/m2. The dark–dark group (n = 10; four males) had a mean age of 26.78 and a mean BMI of 24.25 kg/m2).

Homeostatic model assessments of insulin resistance values were significantly higher in the morning following sleep in the light in the dark–light group, compared with those values in the dark–dark group. This effect was primarily due to increased insulin levels in the group that slept in the light, said the researchers.

“Our preliminary findings show that a single night of light exposure during sleep acutely impacts measures of insulin resistance,” said Dr. Mason. “These results are important, given the increasingly widespread use of artificial light exposure, particularly at night.… More research is needed to determine if chronic overnight light exposure during sleep has long-term, cumulative effects on metabolic function.”

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