Impact of Light Exposure During Sleep on Health Outcomes

In a recent real-world Northwestern Medicine study, older males and females (63 to 84 years of age) exposed to light during sleep at night were substantially more likely to develop hypertension, diabetes, and obesity in comparison to adult individuals who did not have such exposure.

The study participants were a part of the Chicago Heart Association Detection Project in Industry (CHA), a public health program, and an epidemiologic study was conducted between 1967 and 1973 for the identification of adults at an increased risk of cardiovascular disorders in workplaces throughout Chicago.

Almost 40 years later (2007 to 2010), Dr.Zee and Dr. Martha Daviglus, an Adjunct Professor of Preventive Medicine at Feinberg, conducted the Chicago Healthy Aging(CHAS) study with 1,395 survivors of the original CHA study who were willing to participate.

The present cross-sectional study conducted by the researchers comprised 552 participants for whom, exposure to light was monitored using actigraphy devices worn on the wrists of their non-dominant hands and the measurements were tracked for a period of seven days. In addition, the participants filled out a sleep diary daily. The participants were also subjected to detailed examinations of blood pressure (BP), height, weight, glucose, cholesterol, and other established risk factors for cardiovascular disorders.

The researchers were astonished on finding out that not even half of the study participants had five hours of complete darkness every day with light exposure even during sleep at night.

Dr. Minjee Kim, the corresponding author of the study, a Northwestern Medicine physician and Assistant Professor of Neurology at Northwestern University Feinberg School of Medicine said, 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. 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.”

However, it is not known whether diabetes, obesity, hypertension, or diabetes, caused individuals to sleep with the light on, or if light exposure contributed to the development of the health conditions. Individuals with the conditions may be more likely to wake up from sleep in the middle of the night to use the washroom (with the light on) or there may be other reasons to keep the light on. Diabetic individuals with neuropathy may keep the light on at night to decrease the risk of accidental falls.

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

Dr. Zee and the team are currently considering an intervention study to determine if restoration of the natural light-dark cycle leads to improvements in health outcomes like cognition. In addition, Dr. Zee offered a few tips to decrease light exposure during sleep which are as follows:

  1. Don’t turn the lights on. If you need to have a light on (e.g., for safety), a dim light should be used situated closer to the floor.
  2. The color of the light is an important consideration. A red/orange/amber light stimulates the brain to a less degree. Blue light or white light should be avoided and should be far away from the sleeping area.
  3. Eye masks or blackout shades could be beneficial if outdoor light cannot be controlled. In addition, the bed should be oriented such that the outdoor light does not shine directly on the face.

Other study authors include Matthew Maas, Kathryn Reid, Rosemary Braun, Michael Wolf, and Thanh-Huyen Vu.


Kim, M., et al. (2022) Light at night in older age is associated with obesity, diabetes, and hypertension. Sleep.


Pooja Toshniwal Paharia

Dr. Pooja Toshniwal Paharia is a Consultant Oral and Maxillofacial Physician and Radiologist, M.DS (Oral Medicine and Radiology) from Mumbai. She strongly believes in evidence-based radiodiagnosis and therapeutic regimens for benign, potentially malignant, or malignant lesions and conditions either arising from the oral and maxillofacial structures or manifesting in the associated regions.

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