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Being a night owl can be bad for your heart.

That may sound surprising, but a large study found people who are more active late at night — when most of the population is winding down or already asleep — have poorer overall heart health than the average person.

“It is not like, that, night owls are doomed,” said research fellow Sina Kianersi of Brigham and Women’s Hospital and Harvard Medical School, who led the study. “The challenge is the mismatch between your internal clock and typical daily schedules” that makes it harder to follow heart-healthy behaviors.

And that’s fixable, added Kianersi, who describes himself as “sort of a night owl” who feels a boost in “my analytical thinking” after about 7 or 8 at night.

Heart disease is the leading cause of death in the U.S. The American Heart Association has a list of eight key factors that everyone should heed for better heart health: being more physically active; avoiding tobacco; getting enough sleep and a healthy diet; and controlling blood pressure, cholesterol, blood sugar and weight.

Where does being a night owl come in? That has to do with the body’s circadian rhythm, our master biological clock. It follows a roughly 24-hour schedule that regulates not just when we become sleepy and when we’re more awake but also keeps organ systems in sync, influencing things like heart rate, blood pressure, stress hormones and metabolism.

Everybody’s circadian rhythm is a little different. Prior research had suggested night owls might have more health problems, as well as risk factors like higher rates of smoking and less physical activity, than people with more typical bedtimes, Kianersi said.

To learn more, Kianersi’s team tracked more than 300,000 middle-age and older adults in the UK Biobank, a huge health database that includes information about people’s sleep-wake preferences. About 8% of those people classified themselves as night owls, more active physically and mentally in the late afternoon or evening and up past most people’s bedtime.

About a quarter were early-birds, most productive in the daylight hours and likewise early to bed. The rest were average, somewhere in the middle.

Over 14 years, the night owls had a 16% higher risk of a first heart attack or stroke compared to the average population, the researchers found.

The night owls, especially women, also had overall worse cardiovascular health based on meeting the heart association’s eight key factors, the researchers reported Wednesday in the Journal of the American Heart Association.

Unhealthy behaviors — smoking, insufficient sleep and poor diet — appear to be the main reasons.

“It comes down to the problem of a night owl trying to live in a morning person’s world. They’re getting up early for work because that’s when their job starts but it may not align with their internal rhythm,” said Kristen Knutson of Northwestern University, who led recent heart association guidance on circadian rhythms but wasn’t involved in the new study.

That affects more than sleep. For example, metabolism fluctuates throughout the day as the body produces insulin to turn food into energy. That means it might be harder for a night owl to handle a high-calorie breakfast eaten very early in the day, during what normally would still be their biological night, Knutson said. And if they’re out late at night, it can be harder to find healthy food choices.

As for sleep, even if you can’t meet the ideal of at least seven hours, sticking to a regular bedtime and wake time also may help, she and Kianersi said.

The study couldn’t examine what night owls do when the rest of the world is asleep. But Kianersi said one of the best steps to protect heart health — for night owls and anyone — is to quit smoking.

“Focus on the basics, not perfection,” he said — again, advice that’s good for everyone. —AP

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.