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People with irregular sleep patterns may face substantially higher odds of high blood pressure than those who stick to a schedule, even when they get the recommended amount of sleep each night, new research suggests.

The study, published Tuesday in the journal , found people who slept in on the weekends or varied the times they went to sleep and woke up throughout the week were substantially more likely to have high blood pressure, also known as hypertension, than those with more consistent sleep routines.

"This indicates that people may need to consider not only how long they sleep, but also recognize the importance of keeping a regular sleep schedule for optimal cardiovascular health," said senior study author Danny Eckert, director of the Adelaide Institute for Sleep Health and a professor in the College of Medicine and Public Health at Flinders University in Adelaide, Australia.

The adults get seven to nine hours of nightly sleep to promote optimal heart and brain health. The recommendation is based on prior research that found people who get less than six hours of sleep per night on average face a much higher risk for high blood pressure, obesity, cardiovascular disease and premature death. Likewise, those who get too much sleep – more than an average nine hours per night – face higher risks for high blood pressure, stroke, Type 2 diabetes and death.

The authors of the new study note prior research examining the links between sleep duration, nightly variation in sleep schedules and high blood pressure has relied on data reported over just a few weeks.

In the new study, researchers looked at sleep patterns over a nine-month period for 12,287 adults with and without high blood pressure from 20 countries. Participants were predominantly middle-aged men who were overweight. Data were collected from July 2020 to March 2021. The analysis included an average 181 nights of sleep data and 29 blood pressure readings for each participant.

The study defined high blood pressure as a systolic (top number) reading of 140 mmHg or higher or a diastolic (bottom number) reading of 90 mmHg or above. (The AHA and American College of Cardiology define high blood pressure as a systolic pressure of 130 or higher or a diastolic pressure of 80 or higher that stays high over time.)

The researchers used a device placed under the mattress to measure sleep timing (when people went to sleep and woke up) and duration. They found people whose bedtimes varied by 90 minutes or more faced 92% increased odds for high blood pressure, compared to those who stuck to a regular bedtime. But even those whose bedtimes varied by slightly more than 30 minutes from night to night were 32% more likely to have high blood pressure.

"This is a relatively modest level of sleep timing variability, given that people often stay up late on the weekends," Eckert said.

Sleeping late also was associated with higher odds of high blood pressure, but less so than not getting to bed on time. Waking up 43 minutes later was associated with a 9% increase.

As prior studies have found, the new analysis also showed a link between hypertension and getting too little or too much sleep. People who got less than seven or more than nine hours of sleep were 20%-30% more likely to have high blood pressure. People whose sleep duration varied by two hours or more from night to night were 85% more likely to have hypertension than those with less than an hour's difference in the amount of sleep they got each night.

Studying sleep patterns for nine months provides a more stable data set from which to draw conclusions about how sleep may be affecting heart health, said Dr. Reena Mehra, a professor of medicine and director of the Sleep Disorders Research Program at the Cleveland Clinic Sleep Disorders Center in Ohio. Mehra was not involved in the new study.

"If you're only looking at a span of weeks, that's a much smaller window of time," she said. "If there's something unusual going on in a person's life, that's going to impact the findings. Whereas if you look at sleep patterns in totality over a span of months, that gives you a better picture of sleep-wake habituality."

While work schedules and other commitments can sometimes make it hard to keep regular sleep times, the findings confirm the need for people to "try to be as mindful as possible about sleep," Mehra said. "Do the best you can to get consistency."