A new study published in JAMA indicates that high amounts of artificial light at night can increase a person’s risk of heart disease — and breast cancer — by up to 50%.

The research, led by Uppsala University’s Dr. Jonathan Cedernaes, tracked 89,000 participants for one week between 2013 and 2016. Researchers then followed up with participants roughly eight years later. Higher levels of artificial light at night were linked to elevated risks of coronary heart disease, stroke, atrial fibrillation, myocardial infarction and heart failure.

The study found that the increased risks persisted even after accounting for factors such as sleep duration, sleep efficiency, physical activity and seasonal photoperiod.

While scientists have long noted that light from devices such as cellphones and televisions can affect sleep quality, the study showed that other sources of artificial light can also have adverse effects.

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Conversely, people who were exposed to high amounts of daytime light had lower risks of cardiovascular disease.

“Just as all light is not uniform, neither are we as individuals. Indeed, the light intensity needed to significantly suppress evening melatonin secretion is higher following greater daytime light exposure, and can differ by several 10-fold across individuals,” Cedernaes wrote.

The study suggests that people should reduce unnecessary bright nighttime lighting and optimize 24-hour light exposure to lower cardiovascular risk.