Most people know that it’s important for adults to get around six to nine hours of sleep each night. But a growing body of research suggests that when you fall asleep and wake up each day may be just as important for your health as how much you sleep.
Studies suggest that for optimal health, it’s best to go to sleep and wake up at roughly the same time each day. Having a fairly consistent bed- and wake-time can help ensure that you get the right amount of sleep each night. But it also puts you in alignment with your circadian rhythm, the innate 24-hour clock that governs daily fluctuations in your hormone levels, body temperature, metabolism, digestion and other aspects of your health.
In 2023, a group of international sleep experts published a report on the importance of sleep regularity. They reviewed more than 60 studies and concluded that keeping a regular sleep schedule, with consistent bed and wake times, were linked to improvements in a wide variety of health and performance outcomes, including metabolic health, mental health, daily alertness and academic performance.
“Sleep is much more complicated than just a simple number of hours per night,” said Susan Redline, a senior physician at the Brigham and Women’s Hospital and a professor of sleep medicine at Harvard Medical School who studies the day-to-day consistency of sleep and wake times, known as sleep regularity. “It really does relate to not only the duration or quantity of your sleep but also the quality and consistency of your sleep.”
It’s not just sleep duration that matters, but sleep consistency
One of the largest studies on the health effects of sleep regularity was published last year in the Journal of Epidemiology and Community Health.
Scientists instructed more than 72,000 middle-aged and older adults to wear sensors that tracked their nightly sleep for a week. Then they followed them for up to eight years. They found that people who had the most irregular sleep schedules were 26 percent more likely to experience heart attacks, strokes and other major cardiovascular events compared with people who went to bed and woke up at fairly consistent times each day.
Strikingly, the study found that the irregular sleepers had a heightened risk of cardiac events even if they slept more than seven hours a night.
Another study of about 60,000 adults published in the journal Sleep in 2024 looked at the impact of sleep on mortality. It found that people who ranked in the top 20 percent for sleep regularity — based on factors such as maintaining a reliable bedtime, a predictable wake-up time and a fairly stable duration of sleep — were less likely to die of heart disease, cancer and other diseases during the study period compared with people who ranked in the bottom 20 percent for sleep regularity.
In the study, people who ranked in the top 20 percent for sleep regularity went to sleep and awoke within a roughly one-hour window most days. By contrast, people who scored in the bottom 20 percent for sleep regularity went to sleep and woke up within a roughly three-hour window most days.
Ultimately, the researchers found that sleep regularity was an even better predictor of an early death than sleep duration.
And it’s not just physical health that might be impacted by an inconsistent sleep schedule. Last year, a study in the journal Psychological Medicine found that compared with irregular sleepers, people who kept consistent sleep schedules had a 38 percent lower risk of developing depression and a 33 percent lower risk of developing anxiety. People in the study who slept at least seven hours each night still had a heightened risk of depression and anxiety if they had irregular sleep and wake times.
Why you should stick to a schedule
An irregular sleep schedule can throw off your body’s circadian rhythm, which keeps a vast array of physiological processes on a fairly regular schedule.
Most people have some intuitive sense that their bodies operate on a daily clock. You’ve probably noticed, for example, that you get sleepy at around the same time each night. Or you may notice that, if you set a regular alarm each morning, you’ll eventually start to wake up around that time even without an alarm.
But it’s not just our sleep and wake times that follow a daily rhythm.
Your body temperature typically rises throughout the morning and afternoon, peaks in the evening, and then falls late at night. In both men and women, testosterone levels typically peak in the morning, while growth hormone levels peak at night during sleep. Stress and metabolic hormones such as cortisol and insulin tend to rise in the morning and fall throughout the day, which is why experts say that our bodies are better able to digest and metabolize food earlier in the day rather than later.
“Sleep regularity influences our circadian rhythm, which is critical to almost every physiologic system in the body, including metabolism and cardiovascular function,” Redline said.
Erratic bedtimes and wake-up times can disrupt the hormones and physiologic functions that are regulated by your internal clock.
Jamie Zeitzer, a professor of sleep medicine at Stanford University who studies circadian rhythms, said that sleep timing and regularity are in many ways as important for your health and well-being as the duration of your sleep.
“If you normally go to sleep at 10, your body’s getting ready from the circadian perspective to go to sleep at 10,” he said. “If you don’t, there are problems.”
If you try to go to bed too early, your body won’t be ready for sleep, and you’ll toss and turn. If you stay up much later than usual, that signals to your body that you need to be awake for some important reason, Zeitzer said.
“It kicks in extra mechanisms to help you stay awake,” he added. “It’s like, ‘Oh, you want to stay awake later? Great, let me help you out.’ And so it induces all of these mechanisms that are not normal.”
This explains the phenomenon many people have experienced when they stay up past their bedtime and then find they get a second wind and struggle to fall asleep later on.
How to create a sleep schedule
Some studies suggest that 10 p.m. is the optimal bedtime for most adults. But in reality, there’s no magic number that works for everyone, Redline said. Instead, the ideal bedtime will vary depending on how much sleep you need and what time you need to wake up each morning.
Here is how you can figure out your optimal bedtime and some simple ways to maintain a consistent sleep schedule.
- First, start by figuring out what time you need to be up in the morning, and then work backward to identify your optimal bedtime, Redline said.
- Next, think about how much sleep you need each night to wake up feeling well-rested. Most people generally need between seven and nine hours of sleep each night. If you have to be up at 6 a.m., and you know you need about eight hours of sleep, then ideally you should go to bed around 10 p.m.
- It’s unlikely that you’re going to fall asleep as soon as you get into bed. So, pick a bedtime that’s about 15 minutes before you need to fall asleep, said Redline.
- If you can, try adding in another 15 minutes before your bedtime for a “winding-down” routine. This could mean reading a book, writing in a journal, doing some gentle stretching, meditation or anything else that you find calming.
- In addition to having a bedtime routine, try to create other nightly routines as well. Think about having your dinner at roughly the same time each night. If that’s not possible, then try to schedule an after-dinner walk or some other activity at the same time each night. For a lot of people, especially those who have to work late, this can admittedly be a challenge. But anything you can do to maintain a routine in the evening will help you stick to a consistent bedtime.
- Try to continue your routine on weekends. For many people, that can be tricky. But the more you can maintain your sleep routine on the weekends, the easier it will be to stick to your sleep schedule during the week.
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