Health
10-Year Study: Seven Hours of Sleep Is the Sweet Spot
A decade-long study of 40,000 adults found that seven hours of sleep per night is associated with the best heart health outcomes. The research also found that sleep quality matters more than total hours, and that consistently sleeping more than nine hours carried elevated risk.
Illustration: Clear News
Seven hours of sleep per night is the sweet spot for heart health, according to a 10-year study of 40,000 adults published this week. The research also found that how well you sleep matters more than how long.
The study followed participants across a decade, tracking sleep duration, sleep quality, and cardiovascular outcomes. Researchers used a combination of wrist-worn sleep trackers and annual questionnaires, giving a longer and more objective view of sleep than most prior research.
Adults who averaged seven hours had the lowest rates of heart attack, stroke, and hypertension. Those sleeping fewer than six hours had a 27 percent higher risk of cardiovascular events. Surprisingly, those sleeping more than nine hours also showed elevated risk, a finding the researchers attribute partly to underlying health conditions that cause long sleep.
"Sleeplessness gets all the attention, but oversleeping is also a signal worth paying attention to," said the study's senior author. "The relationship is U-shaped. Both extremes carry risk."
Quality beats quantity
The more striking finding may be about quality. Participants who slept well, meaning they fell asleep quickly, woke rarely, and felt rested, had better heart outcomes than those who slept longer but poorly.
Among people sleeping eight hours, those with fragmented sleep had cardiovascular risk comparable to people sleeping only six hours soundly. The researchers say this reframes sleep guidance: a consistent, restful seven hours beats a restless eight.
"People obsess over the number on their sleep tracker," said a cardiologist not involved in the study. "This says the tracker should be measuring continuity and restfulness too. Seven good hours is the target."
What you can do
The researchers emphasize consistent schedules. Participants whose bedtimes varied by more than an hour from night to night had worse outcomes even when total sleep was adequate. Regularity, the study suggests, may be nearly as important as duration.
The team also found that catching up on weekends did not fully offset short sleep during the week. Sleep debt, it appears, cannot be repaid in bulk.
The study was observational, so it cannot prove that changing sleep habits changes heart risk. But its size and duration make it among the strongest evidence yet for the seven-hour guideline, and a randomized trial testing a sleep-regularity intervention is now being planned.