For pretty much my whole life, I’ve had an irregular sleep schedule. It started in my pre-teen years when I would secretly stay up way past my bedtime with a flashlight and a book, persisted during my teen and college years when I stayed out far too late partying, and peaked in my early parenting years with my child-who-thought-sleep-was-for-suckers.
These days, my partner is constantly urging me to get on a more consistent sleep schedule. I often stay up late scrolling TikTok or reading when I know I need to wake up early to help get my kids off to school. But I love those quiet, dark hours of me-time. Still, since I short myself during the week, I often find myself desperate to sleep in on the weekends. There are few things that bring more bliss than waking up to a bright, sunny room without the sound of an alarm clock. So, I usually go to bed after midnight, and I’m almost always running on fumes.
Sleep And Our Hearts
A new study tells me that, once again, infuriatingly, my partner is right and I should simply follow their advice. A new study has identified a correlation between the time a person goes to sleep and their risk of developing cardiovascular disease. The study, which compiled sleep and heart data from more than 88,000 subjects in the UK Biobank, found that, for a reduced risk of developing heart disease, the ideal time for going to sleep is between 10 p.m. and 11 p.m.
Interestingly, the correlation between sleep time and lowered risk of heart disease does not appear to be a “the earlier the better” type situation. Go to bed earlier than 10 p.m. and the benefit decreases, according to the study.
The Link Between Sleep Onset And Cardiovascular Disease
My first question was, how do they know this isn’t a situation in which people already have undetected heart disease and that fact itself is what’s causing people’s later sleep times? In other words, could it be that the heart issue causes the irregular sleep and not the other way around?
The study authors had the same question. They controlled for it via “sensitivity analyses,” using accelerometer data collected 12- to 18 months after the sleep timing data was taken. Even so, the associations between going to sleep and cardiovascular disease persisted. Of the 88,026 study participants, 3,172 of them developed cardiovascular disease within an average timeframe of 5.7 years. None of these 3,172 subjects had any known heart issues or sleep disorders at the start of the study.
Study authors noted, however, that they couldn’t be sure that other factors weren’t simultaneously impacting a person’s sleep time and cardiovascular health. For example, if a person was going to bed late due to increased stress at work causing insomnia or because they were staying up late drinking, each of those activities could contribute both to later sleep times and an increased risk of heart disease. Also of note is that the study authors only looked at timing and duration of sleep, not quality of sleep. So we don’t know how deeply the study participants were sleeping.
Theories About The Link Between Sleep And Heart Disease
One theory about the link between earlier or later bedtimes and increased risk of heart disease, according to one of the study’s co-authors, Dr. David Plans, is that the earlier or later bedtimes may impact the time at which a person receives morning sunlight cues to wake up. Morning sun doesn’t just alert our conscious brain that it’s time to start the day — it begins a critical daily cycle (circadian rhythms) that establishes and maintains important bodily functions like glucose regulation to inflammation. Dr. Plans, the head of research at Huma Therapeutics and senior lecturer at the University of Exeter, told The Guardian that throwing off these levels can “increase risk of cardiovascular disease.”
But what about the percentage of the world’s population that lives at far north or south latitudes that cause their experience of daylight to fluctuate wildly from season to season? Do those populations all experience a higher incidence of heart disease? I need to know more.
Additional limitations on the study were that participants were predominantly aged 43 to 79 and white. Study authors suggest further research with a more diverse array of participants before making any kind of blanket announcement about an ideal bedtime.
Regardless, the study does point out a noteworthy correlation between the time we go to sleep and our risk of developing cardiovascular disease. I do love that quiet, peaceful hour after my tween and teen have finally gone to bed. But maybe, in the interest of my own longevity, I’ll have to sacrifice it after all. My partner will certainly be pleased.