Exposure to bright light at night can increase heart disease risk

A new study led by Flinders University has found that being exposed to bright light at night can significantly increase the chances of developing serious heart problems, including heart attacks, strokes and heart failure.

Published in JAMA Network Open, the research is the largest study of its kind to explore how personal light exposure affects heart health using data from nearly 89,000 people in the UK.

Using wrist-worn sensors, researchers from FHMRI Sleep Health tracked over 13 million hours of light exposure and followed participants for up to 9.5 years.

The study found that people who were exposed to the brightest light at night were much more likely to develop heart problems, with a 56% higher chance of heart failure and 47% more likely to have a heart attack.

These risks remained high even after accounting for other factors like exercise, diet, sleep habits and genetics.

Dr. Daniel Windred, lead author and Research Associate at Flinders University's FHMRI Sleep Health, says the study highlights a risk factor that many people aren't aware of, but one that's easy to address.

This is the first large-scale study to show that simply being exposed to light at night is a strong and independent risk factor for heart disease.

Disrupting your body's internal circadian clock by repeatedly exposing yourself to bright light at night, when it would typically be dark otherwise, will put you at a higher risk of developing dangerous heart issues.

Thankfully, we do have some control over our exposure to light at night.

By using blackout curtains, dimming lights, and avoiding screens before bed, we can help to reduce the health risks associated with light at night."

Dr. Daniel Windred, Lead Author and Research Associate at Flinders University's FHMRI Sleep Health

The study also found that women and younger people were especially vulnerable to the impact of light exposure at night.

"Women may be more sensitive to the effects of light disrupting their body clock, which supports earlier research findings," says senior co-author, Professor Sean Cain.

"In fact, women exposed to high levels of night light had similar heart failure risks to men, which is unusual because women typically have some natural protection against heart disease."

Senior co-author, Associate Professor Andrew Phillips, says that this isn't just a problem for shift workers or people living in brightly lit cities.

"Everyday habits, like scrolling on your phone in bed or falling asleep with the TV on or bedroom lights on, can expose you to potentially harmful levels of light," says Associate Professor Philips from FHMRI Sleep Health.

"We're not talking about extreme cases, even low levels of indoor light can interfere with your body's natural rhythm."

Unlike previous studies that relied on satellite images or surveys of outdoor light at night, this research used real-time data from wearable devices, giving a much clearer picture of how light in our indoor environments affects health.

With heart disease still the leading cause of death worldwide, the researchers say it's time to treat light at night like other health risks-such as poor diet, lack of exercise, or smoking.

The team is now calling for more research into lighting guidelines for homes, hospitals, and cities to help reduce night-time light exposure.

"We need to take our body clocks seriously," concludes Professor Cain.

"Protecting our natural sleep rhythms could be a powerful way to fight heart disease."