Bright light during meals affects metabolism, lowers effect of insulin: Study

While researchers say they do not understand how light affects insulin resistance and blood glucose, their recent study suggests an environmental impact on how the body processes nutrients.

By Stephen Feller

CHICAGO, May 19 (UPI) -- Blood glucose levels increase with the brightness of light, according to a small study at Northwestern University, suggesting overall metabolism can be affected by the environment one eats in.

Researchers say they do not understand how light affects metabolism, but the possibility that lighting affects how the body handles nutrients could help researchers understand how environmental factors may impact health.


Studies have shown that light sources such as smartphones and televisions affect sleep patterns, and a study in 2014 suggested exposure to morning light could help people lose weight.

The immediate effects of lighting during meals, however, had not been looked at, researchers say.

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"Our findings show that insulin was unable to acutely bring glucose levels back to a baseline level following a meal with bright light exposure in the evening," Ivy Cheung, a postdoctoral fellow in neurology at Northwestern University, said in a press release. "The results of this study emphasize that our lighting environment impacts our health outcomes."

For the study, published in the journal PLOS ONE, researchers recruited 19 healthy adults to randomly be exposed to blue-enriched light and dim light to find its affect on hunger over the course of four days.


All participants were put under dim light on day two as a baseline, before nine participants were then exposed either to 0.5 hours of blue-enriched light after they woke up while 10 were exposed to 10.5 hours after they woke up, in order to expose them to light beyond evening sundown.

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The researchers took subjective measures of hunger and sleep every hour and took blood samples every 30 minutes for four hours per day in association with the light, measuring for glucose, insulin, cortisol, leptin and ghrelin.

All measurements between the groups were similar, researchers reported, but participants who ate breakfast in the light had higher insulin resistance, while those who ate dinner in the light had higher peak glucose.

"These results provide further evidence that bright light exposure may influence metabolism," said Dr. Kathryn Reid, a research associate professor of neurology at Northwestern University. "It's cool that bright light has this effect, but we don't understand why yet. "In theory, you could use light to manipulate metabolic function."

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