Even moderate nighttime light exposure during sleep harms heart health and increases insulin resistance

Nighttime light exposure during sleep may impact metabolic function, according to a new study.

The goal of this study was to see if light exposure during sleep has an unfavorable effect on metabolic results.

Although light exposure during sleep has been found to disturb sleep, these findings suggest that it may also alter metabolism.

“Our preliminary findings show that a single night of light exposure during sleep acutely impacts measures of insulin resistance,” says lead author Ivy Cheung Mason.

Twenty healthy individuals between the ages of 18 and 40 were randomly assigned to one of two groups: Dark-Dark (DD) or Dark-Light (DL) for a three-day, two-night stay. Participants were given eight hours of sleep each night, beginning at their usual bedtime as established by one week of actigraphy with a sleep diary.

The DL group (n=10, 2 males, ages 26.61 ± 4.64 years) slept in the dark < 3 lux on Night 1 and slept in overhead room light of 100 lux on Night 2, while the DD group (n=10, 4 males, ages 26.78 ± 5.15 years) slept in the dark <3 lux on both Nights 1 and 2.

On both nights, polysomnography and hourly blood samples for melatonin were taken. After a night of sleep in complete darkness or 100 lux of light, participants underwent oral glucose tolerance tests on both mornings. Day/Night 1 to Day/Night 2 changes between the DD and DL groups were compared.

Homeostatic model assessment of insulin resistance change values were significantly higher (p<0.05) in the morning following sleep in the light (DL group) compared to sleep in the dark (DD group). This effect was primarily due to increased insulin levels for DL compared to DD group.

The findings reveal that a single night of light exposure during sleep has a significant impact on insulin resistance measurements. Insulin resistance is a condition in which cells are unable to respond to insulin and move glucose out of the bloodstream, and it occurs before type 2 diabetes develops.

“These results are important given the increasingly widespread use of artificial light exposure, particularly at night,” adds Mason “The effect we see is acute; more research is needed to determine if chronic overnight light exposure during sleep has long-term cumulative effects on metabolic function.”

Image Credit: Getty

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