A new study out of the US suggests that any kind of light exposure during sleep can lead to significantly elevated risk of obesity, diabetes and high blood pressure, especially in older adults.

Here at Herculean Strength, we’ve been badgering you to pay attention and get your sleep routine sorted if you want to increase your well-being and maximize your gains. Sleeping properly can DOUBLE your testosterone, for instance.

And this new study is just further evidence for how crucial sleep is to good health.

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Sleep and light exposure: new study

As part of a study of over 500 older men and women aged between 63 and 84, researchers from Northwestern University discovered that harmful light exposure can come from all many different sources, including room lights left on for safety or reassurance, bedrooms that lack proper curtains, and digital devices lighting up at odd hours.

The researchers tracked these individuals for seven days, measuring their exposure to light using wrist-worn devices under real-world conditions. The results showed that older adults who did not get a five-hour period of complete darkness each day were much more prone to develop obesity, diabetes and high blood pressure than those getting uninterrupted sleep.

The researchers discovered that less than half of the 552 participants in their study regularly enjoyed a five-hour period of total darkness each night. What’s more, light was shining on them during the darkest periods of the night and during the middle of someone’s typical sleep cycle – a crucial period for getting the best quality sleep.

“Whether it be from one’s smartphone, leaving a TV on overnight or light pollution in a big city, we live among an abundant number amount of artificial sources of light that are available 24 hours of a day,” says study corresponding author Dr. Minjee Kim, an assistant professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician, in a media release.

“Older adults already are at higher risk for diabetes and cardiovascular disease, so we wanted to see if there was a difference in frequencies of these diseases related to light exposure at night.”

A similar study on ambient light and sleep quality


Another study out of Northwestern University showed that exposure to even a small amount of ambient light at night can disturb your sleep, as well as harming cardiovascular function and increasing insulin resistance the next day.

“The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes and metabolic syndrome,” said senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine.

“It’s important for people to avoid or minimize the amount of light exposure during sleep.”

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The study authors caution, however, that their findings don’t reveal which condition is causing the other. Could obesity, diabetes, and hypertension be causing people to sleep with more lights on? Or are lights causing these changes in the human body?

The authors also note that individuals with these health problems may be more likely to get up and go to the bathroom in the middle of the night — turning on more lights. Others with foot numbness, one of many symptoms of diabetes, may also keep more lights on at night to reduce the risk of falling over.

“It’s important for people to avoid or minimize the amount of light exposure during sleep,” says senior study co-author Dr. Phyllis Zee, chief of sleep medicine at Feinberg and a Northwestern Medicine physician.

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