Researchers analyzed the hospital records of 10,528 patients who suffered the most severe type of heart attack — ST-segment elevation myocardial infarction (STEMI) — over a five-year period.

After examining these records, they found a significant increase in STEMI heart attacks at the start of the work week, with a 13% increase on Mondays.

Why Mondays you may ask? “The reason is probably multifactorial; however, based on what we know from previous research, it is reasonable to assume a circadian element,” says Dublin cardiologist Jack Laffan in a press release.

As you may know, sleep is an integral part of your overall well-being; Poor quality and insufficient sleep can affect the cardiovascular system and metabolic health1.

To maintain a regulated circadian rhythm, it is important to have a consistent sleep and wake time. When your sleep schedule is all over the place (like when you sleep in on the weekends), your body doesn’t know when to produce melatonin, the hormone that signals it’s time to sleep. As a result, your circadian clock may suffer most on Sunday night, which can affect your heart health on Monday morning.