Study: Any Amount of Light While Sleeping Linked to Poorer Health Outcomes

Older individuals who were exposed to any amount of light while sleeping were significantly more likely to be obese, have high blood pressure, and have diabetes.

In individuals aged 63 to 84 years, those who were exposed to any amount of light while sleeping at night were significantly more likely to be obese, have high blood pressure, and have diabetes compared to adults who were not exposed to any light during the night, according to data from a Northwestern Medicine study published in Sleep. In the real world study, investigators used wrist-worn devices to measure and track light exposure over 7 days.

“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,” Minjee Kim, MD, assistant professor of neurology at Northwestern University Feinberg School of Medicine and physician at Northwestern Medicine, said in a statement. “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.”

The results showed that fewer than half of the 552 individuals in the study consistently had a 5-hour period of complete darkness per day. The rest of the individuals were exposed to some light, even during their darkest 5-hour periods of the day, which were usually in the middle of their sleep.

Because of the nature of the study, investigators did not know whether obesity, diabetes, and hypertension cause individuals to sleep with the light on or whether the light contributed to the development of these conditions.

Individuals with the former conditions may be more likely to use the bathroom with the light on in the middle of the night or another reason to have the light on. For example, an individual with foot numbness because of their diabetes may leave the light on to reduce the risk of falls.

Investigators are considering an intervention study to test whether a restoration of natural light-dark cycles improves health outcomes including cognition.

“It’s important for people to avoid or minimize the amount of light exposure during sleep,” Phyllis Zee, MD, PhD, chief of sleep medicine at Feinberg and a Northwestern Medicine physician, said in a statement.

The investigators offered tips to reduce light during sleep, which included keeping the lights off or having a dim light on closer to the floor; using amber or red/orange light instead of white or blue light when sleeping; and using blackout curtains or eye masks, if needed, to reduce the amount of light.

The individuals in the study were enrolled in the Chicago Heart Association Detection project in Industry, which is a public health program and epidemiologic study conducted to identify individuals at high risk for heart disease in workplaces throughout the Chicago, Illinois area. Further, investigators included a detailed examination of known risk factors for heart disease.


Light during sleep in older adults linked to obesity, diabetes, high blood pressure. EurekAlert. News release. June 22, 2022. Accessed June 30, 2022.