Vitality

Bright Light Can Slow Metabolism And Insulin Resistance, Leading To Higher Peak Blood Sugar In The Evening

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Sunlight in the evening may be no good for your metabolism. Pixabay Public Domain

Those trying to control their weight are always seeking ways to boost their metabolism. Some methods, like working out, are pretty well known. Others, including the consumption of spicy foods and laughing, are a bit more obscure. Alternatively, things like fasting have the power to make your metabolism sluggish. According to a new study by scientists from Northwestern University, you can add bright light to the list of seemingly random things that can slow your metabolism.

The researchers found that exposure to bright light increased insulin resistance compared to dim light and caused higher peak blood sugar levels in the evening. Insulin resistance occurs when the body is unable to efficiently move glucose out of the bloodstream, resulting in built up blood sugar. If allowed to remain, such a buildup could result in increased body fat, weight gain, and a higher risk for Type 2 diabetes.

“These results provide further evidence that bright light exposure may influence metabolism,” said Kathryn Reid, senior author of the study and a research associate professor of neurology at Northwestern, in a press release. “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.”

A previous study at Northwestern showed that people who received the majority of their bright light exposure in the morning weighed less than those who received the majority of their bright light after 12 p.m. In addition, mouse studies showed that animals kept in constant light had abnormal glucose metabolism and gained more weight than control mice.

Reid’s team wanted to find out why.

“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,” said Ivy Cheung, first author of the study and a postdoctoral fellow in neurology at Northwestern. “The results of this study emphasize that our lighting environment impacts our health outcomes.”

The team recruited 19 healthy adults for the study, randomizing their exposure to three hours of light exposure starting at either 30 minutes or 10.5 hours after waking. Both the morning and evening groups ate while exposed to light. Then the researchers compared everyone’s results to their dim light exposure as a control.

The results confirmed that the light, which was blue-enriched to make it mimic natural light more than conventional fluorescent light does, altered metabolic function in both morning and evening, but only evening light lead to higher peak glucose. This suggests insulin has a greater inability to compensate for a glucose increase in the evening.

Source: Cheung I, Zee P, Shalman D, Malkani R, Kang J, Reid K. Morning and Evening Blue-Enriched Light Exposure Alters Metabolic Function in Normal Weight Adults. PLOS One. 2016.

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