Featuring: Minjee Kim, MD
Night lights, TV left on, smartphones linked to significantly higher disease rates
In a sample of older men and women ages 63 to 84, those who were exposed to any amount of light while sleeping at night were significantly more likely to be obese and have high blood pressure and diabetes compared to adults who were not exposed to any light during the night, reports a new Northwestern Medicine study.
Light exposure was measured with a wrist-worn device and tracked over seven days.
The study of real-world associations (not an experiment), published in the journal Sleep, demonstrates the prevalence of any light exposure at night being linked to higher rates of obesity, high blood pressure (known as hypertension) and diabetes among older adults.
“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 of artificial sources of light that are available 24 hours of a day,” said study corresponding author Minjee Kim, MD, assistant professor of Neurology in the Division of Neurocritical Care, and a Northwestern Medicine physician. “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.”
Study investigators were surprised to find that less than half of the 522 study participants consistently had a five-hour period of complete darkness per day. The rest of the participants were exposed to some light even during their darkest five-hour periods of the day, which were usually in the middle of their sleep at night.
Because this was a cross-sectional study, investigators don’t know if obesity, diabetes and hypertension cause people to sleep with a light on, or if the light contributed to the development of these conditions. Individuals with these conditions may be more likely to use the bathroom in the middle of the night (with the light on) or may have another reason to keep the light on. Someone with foot numbness because of diabetes may want to keep a night light on to reduce the risk of falls.
“It’s important for people to avoid or minimize the amount of light exposure during sleep,” said senior study co-author Phyllis Zee, MD, PhD, chief of Sleep Medicine in the Department of Neurology, director of the Center for Circadian and Sleep Medicine, and a Northwestern Medicine physician.
Zee and colleagues are considering an intervention study to test whether a restoration of the natural light-dark cycle improves health outcomes such as cognition.
Zee offered tips to reduce light during sleep:
Who are the study participants?
The study participants were originally enrolled in the Chicago Heart Association Detection Project in Industry (CHA), a public health program and epidemiologic study conducted in 1967-1973 to identify high-risk adults for heart diseases in workplaces throughout the Chicago area. The study included a detailed examination of known risk factors for heart disease.
Almost 40 years later (2007-2010), Zee and Martha Daviglus, MD, PhD, now adjunct professor of Preventive Medicine at Feinberg, conducted a separate study (“Chicago Healthy Aging Study (CHAS)”) with 1,395 survivors of the original CHA study who agreed to participate. They underwent another detailed examination of blood pressure, weight, height, cholesterol, glucose and other known risk factors for heart disease. In addition, they wore the actigraphy device on their non-dominant wrists for seven days and filled out a daily sleep diary. Slightly more than half of the actigraphy devices used had the capacity to measure light, which constitute the basis of this new study.
Other Northwestern authors include senior co-author Kathryn Reid, PhD, research professor of Neurology in the Division of Sleep Medicine; Thanh-Huyen Vu, MD, PhD, research associate professor of Preventive Medicine in the Division of Epidemiology; Matthew Maas, MD, MS, associate professor of Neurology in the Division of Neurocritical Care; Rosemary Braun, PhD, MPH; associate professor of Molecular Biosciences in the Weinberg College of Arts and Sciences; and Michael Wolf, PhD, MPH, associate vice chair for research in the Department of Medicine and the James R. Webster, Jr., Professor of Medicine.
This research was supported by the National Heart, Lung, and Blood Institute (grants R01 HL089695, R01 HL090873, R01 HL021010), the National Center for Advancing Translational Sciences (UL1TR001422) and the National Institute on Aging (P30AG059988), all of the National Institutes of Health.
This article was originally published in the Feinberg School of Medicine News Center on July 19, 2022.
Minjee Kim, MD, assistant professor of Neurology in the Division of Neurocritical Care, and corresponding author of the study.
Phyllis Zee, MD, PhD, chief of Sleep Medicine in the Department of Neurology and director of the Center for Circadian and Sleep Medicine.
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