Under the Stars, Not the Streetlights: The Healing Power of Darkness

One of the reasons I enjoy getting outside the city and exploring remote wilderness areas is to get away from light pollution. I always find it awe-inspiring to gaze into a pitch-black sky strewn with countless stars. And the latest science shows that we tend to be happier and healthier when we regularly immerse ourselves in extremes of light bright sunlight during at least part of the day and total darkness when we sleep. This helps to reset our circadian rhythm so that we sleep more soundly at night and are more energized and cheerful during the day.

A Harvard study presented at the American Heart Association’s Annual Scientific Sessions on November 10, 2025, should motivate us to minimize screentime at bedtime and darken our bedrooms before we snuggle under the covers. This fascinating research reports that increased exposure to high levels of artificial light at night appears to raise risk for cardiovascular (CV) disease.

The study showed exposure to artificial light from screens, streetlamps, electronic devices, and other sources at night triggers inflammation in the arteries and provokes a stress response in the brain, which in turn exerts a strain on the CV system. Individuals with the highest doses of light exposure at night had a 35% increased risk for a major heart event.

Lead researcher on the study Shady Abohashem, MD, MPH, from Harvard Medical School said, “Prior research has shown that light at night disrupts our body’s natural circadian rhythm, while our work demonstrates that it also activates stress centers in the brain and triggers inflammation in the arteries, a combination that we’ve previously found to increase heart disease risk.” 

The findings are not definitive, but they do support the theory that avoiding exposure to artificial light at night may calm stress pathways in the brain and reduce arterial inflammation, which may translate into a lower risk for developing heart attack, stroke and CV death.  

“For individuals living in areas with high light pollution, we recommend minimizing unnecessary sources of artificial light. That means keeping the bedroom as dark as possible, using blackout blinds, eye masks, dimming lighting, and reducing screen time in the hours before sleep,” Dr. Abohashem said. 

Emerging evidence suggests that excessive ambient light during sleep in other words, failing to sleep in a truly dark bedroom may carry implications beyond mere sleep disruption: It may increase cancer risk. Studies show that exposure to artificial light at night suppresses ­melatonin, a hormone that normally rises in darkness and plays a role in regulating the body’s night signals, as well as possibly exerting anti-cancer effects. A 2023 meta-analysis found that higher indoor or outdoor nighttime light exposure was modestly associated with a higher risk of breast cancer in women.

A global ecological study reported significant positive correlations between artificial light at night and incidence rates of breast, colorectal, lung, and prostate cancers.

The theory is that light at night disrupts circadian rhythm, lowers melatonin, alters hormone secretion and sleep quality, and increases inflammation and oxidative stress all known risk factors for both cancer and CV disease.  

Research shows that even dim light in your bedroom from a nightlight, phone charger, or streetlight through the blinds can interfere with melatonin production and disrupt circadian rhythms and may even raise long-term risks for conditions like obesity, diabetes, cancer, and CV disease. To protect your sleep and overall health, aim for total darkness: Turn off electronic devices, cover glowing clocks, use blackout curtains, or try a soft eye mask. Cool, quiet, and dark are the three pillars of good sleep hygiene and sleeping in darkness is one of the simplest ways to help your body heal, renew, and protect itself every night.