Bedroom Light Exposure at Night: A Hidden Risk to Blood Glucose Metabolism and Cardiovascular Health

Jun 08, 2025 | 0 comments posted by Nature Target

Do you fall asleep peacefully in complete darkness, or do you rely on a nightlight for comfort? Do you drift off while watching your phone or television, or do you turn off all electronic devices early and rest with your eyes closed? The glow from bedroom lamps, TV screens, and smartphones may seem insignificant, but these light sources could be quietly compromising your health and the quality of your sleep.

A recent study has uncovered intricate connections between nighttime light exposure and our metabolic health.

Bedroom Light at Night Impairs Glucose Metabolism

In January 2025, a study shed new light on the relationship between bedroom lighting and glucose metabolism. Researchers emphasized that maintaining darkness in the bedroom at night may help prevent glucose metabolism disorders.

The study recruited 256 students aged 16 to 22. Using portable light meters, researchers measured bedroom illumination over two consecutive nights and recorded participants’ sleep duration over seven days and dietary intake over a 24-hour period.

Findings revealed a significant association between light intensity and duration in the bedroom and biomarkers of glucose metabolism. For each standard deviation increase in light intensity, insulin levels rose, along with the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and the triglyceride-glucose (TyG) index. These associations were especially pronounced in individuals who had later eating schedules.

Insulin resistance, a condition where the body becomes less responsive to insulin, hinders effective blood sugar regulation and is a known precursor to type 2 diabetes.

Specifically, participants exposed to higher bedroom light intensity or light exposure exceeding 50 minutes during the night showed significantly elevated glucose metabolism markers compared to those in low-light environments.

These findings highlight the close link between nighttime light exposure and metabolic health. The researchers recommend maintaining a dark sleeping environment to support healthy glucose metabolism.

Nighttime Bedroom Lighting Also Affects Cardiovascular Health and Increases Obesity Risk

Previous research has also demonstrated that nighttime light exposure in the bedroom can negatively affect cardiovascular function and contribute to weight gain.

Exposure to Light at Night Increases Obesity Risk

A 2019 longitudinal study published by the U.S. National Institutes of Health in *JAMA Internal Medicine* followed over 40,000 women for five years. The study concluded that women exposed to artificial light while sleeping were more likely to gain weight—especially those who kept lights or televisions on in the bedroom overnight.

Researchers categorized light exposure as: no light, small nightlight in the room, light from outside the room, or having a room light or TV on while sleeping.

Results showed that women who slept with indoor lights or a television on experienced an average weight gain of 5 kilograms during the follow-up period.

Light Exposure at Night Affects Cardiovascular Health

A 2022 study from Northwestern University, published in *Proceedings of the National Academy of Sciences*, found that sleeping with lights on can impair cardiovascular function and increase insulin resistance—both risk factors for heart disease and diabetes.

Researchers divided 20 healthy young adults into two groups:

One group slept under dim lighting for two consecutive nights.
The second group slept under dim lighting the first night and moderate lighting the next.

The study revealed that brighter nighttime light exposure kept the body in a heightened state of alertness, raising heart rate during sleep. Over time, this sustained cardiovascular stress could contribute to declining cardiometabolic health.

How to Reduce Light Exposure and Improve Sleep Quality

Here are several practical strategies to minimize light exposure at night:

Use Blackout Curtains

Install blackout curtains to block outdoor light, and close them fully during sleep. If complete darkness is not achievable, consider using a sleep mask.

Use Localized Lighting in the Bedroom

Opt for low color-temperature light sources to create a calming, relaxing atmosphere. Bedrooms serve multiple purposes—resting, sleeping, dressing—so a combination of general and task lighting is ideal. For example, use bedside table lamps or wall sconces for the sleeping area, supplemented by ceiling lights for general illumination. This setup avoids overly bright lighting that may harm vision or cause glare off furniture surfaces.

Avoid Bright Lights During Nighttime Awakenings

For older adults or those who frequently wake during the night, consider soft nightlights (0.8–2 watts) rather than bright overhead lights or harsh phone flashlights. Position nightlights close to the floor and away from direct eye exposure.

Limit Electronic Device Use in the Bedroom

Minimize the use of devices such as smartphones, televisions, and computers—especially before bed. These gadgets emit light, produce noise, and generate heat, all of which may disrupt sleep.