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

After examining those records, they noticed a significant increase in the rate of STEMI heart attacks at the start of the workweek, with a 13% increase specifically on Mondays. 

Why Mondays, you might ask? “The cause is likely multifactorial; however, based on what we know from previous studies, it is reasonable to presume a circadian element,” notes Dublin-based cardiologist Jack Laffan in a news release. 

As you may know, sleep is integral for your overall well-being; poor quality and inadequate amounts of sleep can impact cardiovascular and metabolic health1. 

And having a consistent bedtime and wake-up time is essential to keeping a regulated circadian rhythm. When your sleep schedule is all over the place (like, say, when you sleep in on the weekends), your body doesn’t know when to produce melatonin, the hormone that signals that it’s time to go to sleep. As a result, your circadian clocks may suffer most on Sunday nights—which can impact your heart health come Monday morning.