Light Exposure Overnight Raises Risk of Heart Disease & Strokes

For thousands of years our human ancestors slept in the dark. There were no lights inside or outside. That meant that when candles or oil lamps were snuffed out at night, people had very little light exposure. Today, though, we are surrounded by lights both inside and outside. Most cities are awash in light pollution. Many people like to leave some light on in the bedroom. It can seem reassuring, especially if you have to get up in the middle of the night to go to the bathroom. Could light exposure at night have negative health consequences? A new study suggests it can (JAMA Network Open, Oct. 23, 2025).

Light Exposure and Cardiovascular Disease:

We all live by what scientists call our “circadian rhythm.” This cycle is based upon a 24-hour internal body clock. The word “circadian” is based upon the Latin roots “circa” which means around or about and the word “diem” or day. Put them together and you get “about a day.”

The authors of the article in JAMA Network Open explain the importance of this internal clock:

“Robust circadian rhythms are vital for healthy cardiovascular function. Circadian rhythms have been observed in systolic and diastolic blood pressure; platelet activation; fibrinolysis, vascular endothelial function; circulating cortisol, epinephrine, and norepinephrine; glucose tolerance; and heart rate average, heart rate variability, QT interval [electrocardiogram measurement], and PR segment [also ECG measurement]. Short-term circadian disruption in humans causes hypercoagulability [blood clotting potential], elevated heart rate, elevated blood pressure, inflammation, and reduced cardiac vagal modulation. Long-term circadian disruption in animal models causes myocardial fibrosis, hypertrophy, impaired contractility, adverse cardiac remodeling, and accelerated progression to heart failure.”

That is quite technical, but I bet you figured out that “disruption” of our circadian rhythm is not good for the body. The authors go on to point out that such disruption can increase the risk for cardiovascular diseases including atherosclerosis, CAD (coronary artery disease) and high blood pressure.

The Scientific Study of Light Exposure:

The UK Biobank study involves more than 500,000 volunteers. They were recruited between 2006 and 2010 and have been the source of some valuable health information. In this study, more than 100,000 participants wore light-tracking devices on their wrists for one full week between 2013 and 2016. The data that were collected on health outcomes lasted until November 2022.

The researchers carefully tracked health outcomes and compared them to light exposure. Here are the results in the authors own words:

“In this cohort study, across approximately 13 million hours of personal light exposure data, and approximately 700 000 person-years of follow-up, individuals exposed to higher levels of night light had higher risks for incident coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke. These associations of night light with cardiovascular disease risk were robust to adjustment for cardiovascular risk factors including physical activity, diet, sleep, and genetic susceptibility. These findings support night light exposure as an important risk factor for adverse cardiovascular health.”

“The observed associations of brighter night light with higher cardiovascular disease risks are consistent with previous studies of outdoor night light. We observed a 23% to 32% higher risk of coronary artery disease, and a 45% to 56% higher risk of myocardial infarction for people with the brightest nights (91st to 100th percentiles), compared with those with the darkest nights (0 to 50th percentiles).”

Should you wish to better understand the reasons why light exposure disrupts circadian rhythm and increases the risk for cardiovascular disease, check out the original article at this link.

The researchers point out that cardiovascular disease is a leading cause of sickness and death worldwide. Most healthcare professionals encourage their patients to eat a healthy diet, exercise and avoid tobacco products. Rarely do they mention anything about circadian rhythms and light exposure.

The authors conclude their research:

“To our knowledge, this is the first study of personal light exposure patterns and incident cardiovascular diseases, indicating night light as an important new risk factor. Our findings demonstrate that, additional to current recommendations, avoiding night light is a promising target for preventing cardiovascular diseases.”

Some folks might rightly say that they need a night light to safely find their way to the bathroom in the middle of the night. What’s the answer to that conundrum? Stumbling around in the dark could lead to a fall and that would be extremely dangerous, especially for an older person.

The answer is as simple as a sleep mask. Leave a night light on and just remove the sleep mask before getting out of bed. The one I personally like is the Manta Sleep Mask, but there are lots of others to choose from.

The People’s Pharmacy is reader supported. When you buy through links in this post, we may earn a small affiliate commission (at no cost to you).

Interior Lighting Is

You may have heard advice to lower light levels as bedtime approaches. People exposed to bright light indoors have lower levels of melatonin, a hormone essential for sleep. But interior lighting is not the only problem.

Outdoor light pollution has become common worldwide. Most cities use bright light outdoors at night so people can travel safely. But when people are exposed to artificial outdoor light at night, they may experience unexpected harmful effects.

Studying the Effects of Outdoor Light Overnight:

Chinese researchers analyzed light exposure and medical records of more than 28,000 people in Ningbo, China (Stroke, April 2024). They used satellite maps to figure out where the street lights and other nighttime light sources were brightest. After six years of follow-up, those with the highest exposure to outdoor light overnight were 43 percent more likely to develop cerebrovascular disease than those with least exposure. That includes both ischemic and hemorrhagic strokes.

Air Pollution Is an Independent Risk Factor:

Air pollution has also been linked to a higher risk for Parkinson disease as well as heart problems. Consequently, the researchers checked its effects in Ningbo. They found that it too increased the risk for strokes.

People who were exposed to the highest levels of particulates from burning wood, gasoline, oil or diesel fuel were 41 percent more likely to develop cerebrovascular disease than those with the lowest exposures. The investigators suggest that air pollution, covering most particle sizes, may increase inflammation. This in turn could contribute to atherosclerosis or high blood pressure, both risk factors for strokes.

The hazards of air pollution and light pollution appear to be independent.

According to the lead researcher,

“Our study suggests that higher levels of exposure to outdoor artificial light at night may be a risk factor for cerebrovascular disease…Therefore, we advise people, especially those living in urban areas, to consider reducing that exposure to protect themselves from its potential harmful impact.”

Learn More:

We discussed ways to protect yourself and your family from indoor air pollution with Dr. Richard Corsi.

For decades, cardiologists have focused on cholesterol as the key risk factor for heart disease. What if there were other really important elements in the evolution of cardiovascular disease?

You have just read about light exposure as one key contributor to coronary artery disease, heart attacks, heart failure and atrial fibrillation. There is another crucial factor in this week’s health news. It has to do with infections. When is the last time a cardiologist asked you about your exposure to upper respiratory tract infections? They may play a critical link, however.

An article in the New York Times (October 29, 2025) is titled:

“Covid and Flu Can Triple Your Risk of Heart Attack”
“A new analysis adds to the research about the link between viral infections and heart disease.”

You can read all about the latest research that links infection to heart disease at this link:

“How COVID, Flu and Other Infections Cause Heart Disease”
Doctors blame heart disease on bad cholesterol. What if infections cause heart disease? From COVID to gum disease, germs can harm the heart.

A Few Favors Please:

Here at The People’s Pharmacy we strive to keep you informed about the latest health research. There are only two of us…Joe and Terry Graedon. In addition to preparing these newsletters each week, we write 3 nationally syndicated newspaper columns distributed by King Features. And we host a nationally syndicated public radio show heard on over 200 NPR stations and repeaters. And there is also a podcast.

We love what we do, but it takes a lot of time to read, research and write these articles. To keep this website going strong, we need your support. Please let friends and family know about the articles you find helpful. You can do that by scrolling to the top of the page and sharing them via email and social media.

Your financial support is also extremely meaningful.You can eliminate the ads that frequently pop up in the middle of an article. We wish we did not have to support this website with such advertisements, but we would go dark without them. You can eliminate the ads by supporting this website for $5 a month…about the cost of a nice cup of coffee. Here is a link to go ad-free. Not a fan of a monthly charge to your credit card? How about a one-time donation? Here is a link for that.

We have been writing for more than 50 years. We have another book we are very anxious to complete, but it is hard to finish this book with all the writing we are currently doing for our newspaper clients, radio listeners and newsletter subscribers. That is why we are seeking partners to help share the responsibilities. If you know of any healthcare professionals who share our values and passions and who might be interested in exploring a partnership, please send contact information to:

questions@peoplespharmacy.com

Thank you for your support and encouragement.