We all know sleep is important. But most of us focus on how much sleep we're getting, not the time we're actually drifting off. But a major study has turned that assumption on its head, and you're going to want to pay attention if you consider yourself a night owl.
According to research published in the European Heart Journal, drawing on data from over 88,000 UK Biobank participants aged 43 to 74, the time you fall asleep could have a significant impact on your risk of heart and circulatory disease. Participants wore wrist trackers over the course of a week to record their sleep and wake times, answered detailed lifestyle questionnaires, and were then followed for six years - during which time over 3,000 of them developed heart and circulatory disease.
© Getty ImagesThe results, once adjusted for age, smoking status, and other cardiovascular risk factors, were striking. People who fell asleep between 10pm and 11pm had the lowest risk of developing heart and circulatory disease. Those who went to bed between 11pm and midnight had a 12 per cent greater risk, but that figure jumped up to 25 per cent for those who fell asleep at midnight or later.
There was a difference depending on gender, too, with sleep timing appearing to have more of an impact on women than men.
Why bedtime could be more important than you might think
So what's actually going on inside the body when we push our bedtime later? Dr. Raj Dasgupta, Associate Professor of Clinical Medicine at the University of Southern California, who specialises in sleep medicine, explains to Best Quality Designer Handbag that it comes down to the body's internal clock.
"Your body's 24-hour internal clock has an influence on blood pressure, heart rate, inflammation, and metabolism," says the expert, who has appeared on TV shows The Doctors and Chasing the Cure. "When sleep timing is inconsistent or usually late, it can disrupt these systems."
The researchers behind the study suggest that falling asleep at the right time may help ensure you wake naturally with the morning light, a cue that helps regulate your circadian rhythm. However, when that rhythm is thrown off, it can have a significant impact on the cardiovascular system. There is growing evidence that disrupted circadian patterns are linked to elevated blood pressure and an increased risk of heart disease.
But it's not just when you go to sleep that matters, it's also how much. "Short sleep, usually under seven hours each night, is related to high rates of hypertension, stroke, and cardiometabolic disease," Dr Dasgupta warns us. "Poor sleep and untreated sleep apnoea can also further increase cardiovascular strain."
Why sleep should be a priority for heart health
© Getty ImagesThe American Heart Association recently updated its cardiovascular health framework, expanding its guidance from "Life's Simple 7" to "Life's Essential 8," and officially added sleep duration as a critical factor in heart and brain health. The new guidelines recommend seven to nine hours of sleep per night for adults.
"The most practical steps are simple," says Dr Dasgupta. "Try to sleep about seven to nine hours each night, keep a consistent bedtime schedule, limit late-night light exposure on screens, and look into symptoms like loud snoring or daytime fatigue."
It's worth noting that the study doesn't prove late bedtimes cause heart disease, and researchers are careful to stress that further work is needed to fully understand the relationship between the two. However, there is a definite link between the two, and the message from sleep specialists is clear. "Sleep is not just rest," Dr. Dasgupta says. "It is active cardiovascular recovery."
