Getting enough sleep with few interruptions does not guarantee cardiovascular health, according to a study. The 10-year tracking research found that inconsistent bedtimes after age 40 can disrupt the body's biological rhythm and strain the heart.
According to a paper published in BMC Cardiovascular Disorders, introduced by U.S. health outlet Men's Health, researchers examined the correlation between the variability of bedtimes in adults aged 40 to 60 and the risk of developing cardiovascular disease. The researchers concluded that beyond sleep duration and sleep quality, the regularity of when one falls asleep can also be a variable that determines heart health.
The study involved 3,231 people who were an average of 46 years old at the outset. The researchers tracked their bedtimes and wake-up times to identify individual sleep patterns, then analyzed changes in medical records over 10 years. As a result, 128 people experienced major cardiac events including unstable angina, stroke, heart failure, and heart-related death.
Even after controlling for other variables such as body mass index and cholesterol levels, bedtime irregularity was commonly observed in these groups. In particular, cases where the time of falling asleep changed daily and daily sleep fell short of eight hours showed twice the risk of heart problems compared with cases that did not. In contrast, variability in wake-up time showed no clear association with heart risk. The researchers explained that when it comes to heart health, consistency in bedtime may have a greater impact than wake-up time.
Laura Nauha, a postdoctoral researcher at the University of Oulu in Finland and the paper's first author, said the regularity of bedtime may be closely related to heart health. She explained that the consistency of bedtime is an indicator that reflects daily rhythm and its degree of fluctuation.
Behind bedtime acting as a variable is the biological rhythm. The biological rhythm is a biological clock that controls when bodily functions operate, coordinating the timing of eating, rest, and sleep. Dr. Sudha Tallavajhula, a neurophysiologist and sleep medicine specialist at UTHealth Houston, explained that the biological rhythm is also connected to hormone secretion, heart rhythm, and blood pressure regulation. These functions are all directly linked to cardiovascular health.
Dr. Grant Bailey, a cardiologist at South Denver Cardiology and AdventHealth Littleton, said that continuously changing bedtime throws off the biological rhythm. He explained that disruption of the biological rhythm can increase the secretion of stress hormones and adrenaline, affecting heart rate and blood pressure.
Changes in sleep patterns also affect appetite-regulating hormones. This may lead to unbalanced eating habits, and if sleep deprivation persists, the risk of anxiety and depression can rise as well.
Dr. Tallavajhula explained that during sleep, the body transitions from a state centered on activity and digestion to one where recovery, hormone regulation, and memory consolidation take place. This recovery process is a function needed by both the heart and the brain, she said. She said that when sleep quality declines, the heart is placed under continuous stress and cannot secure time to recover. She added that the awareness that the three elements of sleep quality, quantity, and timing are equally important has recently been spreading.
