The calendar may be one more tool that can help you gauge your heart risk: The season and day of the week can influence your chances of having a heart attack, new research from Sweden suggests.

In the study, researchers analyzed data from over 156,000 hospital admissions for a heart attack over seven years. They discovered a few surprising differences in heart attack timing.

When looking at day of the week, the most heart attacks occurred on Mondays, and the least on Saturdays. In fact, the risk of heart attack was 11 percent higher on Mondays than control days, which the researchers defined as Tuesdays through Fridays.

Young, working people seemed most vulnerable to the Monday increase—their risk of heart attack was 20 percent higher on the first day of the workweek.

And when looking at months, December was most risky, while July logged the least number of heart attacks. Relatedly, summer vacations in July were safer for the heart than winter holidays like Christmas and New Year’s.

The times when heart attacks were higher coincide with perceived high and low levels of stress—say, for instance, returning to work on a Monday morning, the researchers say. And it’s possible that stress can trigger changes in your biological system that can leave you vulnerable to a heart attack, as we previously reported. (These 4 food pairings can protect your heart.)

As your stress levels rise, so does the action in a part of your brain called your amygdala, says Ahmed Tawakol, M.D., who has studied the physiological effects of stress but was not involved in the present study. This triggers your bone marrow to churn out more immune cells to fight the stress. But this increase can also cause a spike in inflammation, which can hurt your arteries and your heart. (For more health news delivered right to your inbox, sign up for our Daily Dose newsletter.)

It’s also possible that the Monday spike could be due to delays seeking care over the weekend, the researchers believe. But when they adjusted the data to take into account the timing of symptom onset, the results still remained significant—suggesting that high and low stress timing does play a role in heart attacks.

So try to tamp down your stress to help your heart. The good news is, proven stress-reduction techniques—be it exercising, deep breathing, or even watching a funny movie—can reduce the activity of the amygdala, says Dr. Tawakol. Try these 19 ways to live a stress-free life to calm your racing mind—and protect your heart, too.

Additional reporting by Elizabeth Millard

Christa Sgobba For nearly 10 years, Christa has created health, fitness, nutrition, and wellness content that’s steeped in science but engaging enough that people actually want to read it.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io