Light at night can increase heart disease risk

It turns out that being exposed to bright light at night can significantly increase your chances of developing serious heart problems, including heart attacks, strokes and heart failure. That’s according to a new study led by Flinders University and published in JAMA Network Open, which utilised data from nearly 89,000 people in the UK.

Unlike previous studies that have relied on satellite images or surveys of outdoor light at night, this research used real-time data from wrist-worn sensors, giving a much clearer picture of how light in our indoor environments affects health. Using these devices, 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 factors like exercise, diet, sleep habits and genetics.

“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,” said lead author Dr Daniel Windred, a research associate at FHMRI Sleep Health.

“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.

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,” said senior co-author Professor Sean Cain, also from FHMRI Sleep Health.

“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, also from FHMRI Sleep Health, said 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,” he said.

“We’re not talking about extreme cases; even low levels of indoor light can interfere with your body’s natural rhythm.”

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, with Windred encouraging people to take control over their own exposure where possible.

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

Image credit: iStock.com/Leonid Sorokin