People whose bedtimes changed more from night to night showed a 23% higher risk of serious cardiovascular events in a major US study drawing on more than one million nights of recorded sleep.
Published November 2 in the American Heart Association journal Circulation: Population Health and Outcomes, the research analyzed Fitbit and medical records from 10,362 adults enrolled in the US National Institutes of Health’s All of Us Research Program. Researchers assessed sleeping patterns over six months and followed participants for a median of 3.7 years.
During that period, 230 participants developed conditions included in the study’s combined cardiovascular outcome, which covered heart attacks, ischemic strokes, heart failure and cardiomyopathy, a disease affecting the heart muscle.
Inconsistent wake-up times were associated with a 20% higher risk of the combined outcome. Each 29-minute increase in the statistical variation of nightly sleep duration was linked to a 24% higher risk.
Researchers also found that average sleep duration was not significantly associated with the combined outcome in their analysis, drawing greater attention to the consistency of sleeping patterns.
“Sometimes the quality of sleep is something we cannot control. But the regularity, consistent bedtimes throughout the week and waking up at the same time every morning, is something some people can control,” said neuroscientist Nguyen Minh Tuan Viet of Boston Children’s Hospital and Harvard Medical School.
The findings carry practical relevance for Filipinos working overnight, rotating shifts or regularly changing their sleeping hours. The country’s IT and business process management industry employed approximately 1.9 million people in 2025, according to its industry association. Viet also identified weekend schedule changes as a common source of irregular sleep.
The American Heart Association recommends seven to nine hours of sleep for adults and consistent bedtimes and wake-up times. The new findings highlight an everyday habit that workers and families can monitor as they take greater care of their cardiovascular health.
