You’ve probably heard the phrase “circadian rhythm” before. At some point in your life, you’ve also probably blamed a random health issue on your body clock being “off.” And you may have been right: Your circadian rhythm is actually pretty important when it comes to many aspects of your well-being, ranging from your metabolism, to your sleep, to your immune system function.
To be honest, though, we were a little fuzzy on the details of how a person’s circadian rhythm system actually operates. So, we chatted with Brandon R. Peters, M.D., all about what controls these internal clock processes and what messes with them, as well as why they are such powerful influences when it comes to your overall health. Dr. Peters is a double board-certified neurologist and sleep medicine physician who practices at Virginia Mason Medical Center in Seattle. He is also a clinical affiliate at the Stanford Center for Sleep Sciences and Medicine and the author of Insomnia Solved.
SELF: How would you define circadian rhythm in layman's terms?
Dr. Peters: So the term “circadian” was coined by Franz Halberg in 1959. It comes from Latin words meaning “about a day.” Circadian rhythm is an umbrella term that describes numerous processes in the body that follow a 24-hour schedule. There are a number of things that follow this daily schedule, and the body has a system in place that’s really meant to measure time.
SELF: So what does your circadian rhythm do, exactly?
Dr. Peters: Several physiological processes are timed to patterns of light and darkness. This includes metabolism, hormone levels, and body temperature. The circadian rhythm matches what happens within our body to what occurs in the environment. For example, our body temperature naturally takes a dip around 4 A.M., and this roughly corresponds to the coldest part of the night, which may help to reduce heat loss. Sleep and wakefulness are also ideally synchronized to the patterns of light and darkness. How our body uses energy is also timed to our access to food.
SELF: And what controls your circadian rhythm? Is it something that’s set at birth?
Dr. Peters: There are two main things that control your circadian rhythm: the internal biological clock system and external synchronizing cues. Our internal sense of time, called tau, is genetically determined. In other words, our internal rhythms persist even if we are placed in a cave where light and temperature variations are nonexistent; we would still follow a nearly 24-hour schedule. We would sleep about eight hours and be awake about 16 hours, even if we didn’t experience night and day.
In reference to the external time cues, light is the main controller of the circadian rhythm and really dictates the timing of the body clock, especially in regards to sleep and wakefulness. It enforces a more direct connection to the natural environment. The key thing for most folks is getting morning sunlight. You closely align wakefulness with when you are exposed to natural light, and sleep is more likely to occur overnight when you aren’t.
SELF: Does your circadian rhythm stay the same throughout your life?
Dr. Peters: There is seasonal variation, and variation through the lifespan as well. Some of this is to do with changes in natural sunlight exposure. For example, in the wintertime, you may not be able to get sun right when you are waking up. You may have to use an artificial source of light if you want to maintain a consistent circadian rhythm year round. There is also evidence that teenagers are more likely to be night owls, and that older people may develop some gradual advancement in the timing of their sleep period.
SELF: What external factors can affect or throw off your circadian rhythm?
Dr. Peters: The primary one in sighted individuals is light. In totally blind people who cannot see light, melatonin is a big one. Environmental temperature, exercise, social activities, and meal timing are also all things that can affect the circadian rhythm. When they are consistently timed, they may be useful as external cues (called zeitgebers, which is German for “time-givers”).
The part of the brain that controls circadian timing is the suprachiasmatic nucleus within the hypothalamus. It’s located in the front of the brain, and light travels through the optic nerves from the eyes to the front of the brain. Moreover, every cell in the body has a way to track circadian patterns. So if you isolated skin cells or heart cells or even fat cells, for example, they will still follow circadian schedules. The brain and hormones work together to synchronize all of your body’s separate systems.
Another thing worth mentioning is that our bodies really like routine and regularity. We eat and go to the bathroom at generally the same times during a day. And our bodies adopt certain cues from our routine. Especially for blind subjects who lack light perception, seemingly small elements in a routine can actually become very strong signals.
SELF: Is there any way to change your circadian rhythm? For instance, I consider myself a night owl. Waking up at 6 A.M. is painful for me, but I’d love to be more of a morning person. Is that even possible for me long term?
Dr. Peters: About 10 percent of the population would be considered a night owl, which we also refer to as delayed sleep phase syndrome. But that can also be changed. The key to setting your circadian rhythm is waking up at the same time every day and getting direct sunlight exposure within 15 minutes of waking. It is always brighter outside than indoors, so natural light works better.
Blue light is the part of the light spectrum that shifts our circadian timing. So, we also need to limit our exposure to artificial light before bed. That might mean reducing the use of small screens an hour or two before bedtime, especially for a night owl who wants to become a morning person.
SELF: But if you try and fight your natural rhythm, will your body want to push back? I've tried this circadian shift before, and I eventually just fall back into my old patterns.
Dr. Peters: It depends on how much you’re attempting to shift your patterns. If you’re changing from waking up at 10 A.M. to 6 A.M., that might take you a while. If you’re moving your schedule 15 to 30 minutes perhaps a week at a time, it may take a month or more. But it’s better to do it gradually. And it’s easier to adhere to it that way.
I don’t think it’s necessarily impossible for you to change your circadian schedule, but if you’re falling into old patterns where you feel more awake at night and are still having trouble getting up in the morning after a while, it’s possible you are not really committing to changing all of the factors we’ve discussed. Are you powering off your electronics with adequate time before bed, and are you exposing yourself to light as soon as you wake up? Are you also shifting, for example, your dinner schedule accordingly? Or when you have morning coffee? Just changing your sleep and wake time may not be enough without adjusting these other cues. I do think that with some effort it is possible to keep to a new schedule, even if it’s not what you would consider your naturally preferred schedule. It requires consistency. But as I said, a consistently fixed wake time and morning sunlight exposure immediately upon awakening are key.
Any time there is something off with a person’s routine, their genetic predisposition will come out again. So if you do not maintain consistency, your genetic predisposition, possibly of being a night owl as you describe, will return. But if the person keeps to the routine, they can sleep the same hours as everyone else. Most people with delayed sleep phase disorder have a family history of the disorder. So in that case, a new routine may be harder to achieve without addressing the social influences. If everyone else stays awake late and sleeps in, you would be less likely to adhere to the new routine.
SELF: Can you circadian rhythm affect your health at all?
Dr. Peters: The most common symptoms associated with a circadian rhythm issue are insomnia and sleepiness at improper times. A night owl may have sleepiness that persists into the start of the day, like at work, and wanting to go back to bed or not wanting to get up. Sleep deprivation, which many people with circadian rhythm-related issues experience, opens up a whole Pandora’s box because so many things are then affected, from your metabolism to immunity.
Chronic sleep deprivation is associated with many health issues. Sleep deprivation may also have the power to worsen certain chronic medical issues. The reality is we are just now learning a lot about the powerful effects of sleep deprivation. Circadian rhythm has been described for about 60 years, and the genetics have been understood since 1994. But we’re still learning a lot about the relationship between how circadian rhythm affects overall health. There is a lot more that we just don’t fully understand. There are probably a lot of implications of this science in many different aspects of health that we have yet to uncover.
For instance, there is interesting research going on in regards to how surgeries might be more successful at certain times pegged to someone’s circadian rhythm. Or, it may be better to take medication at certain times depending on the person and their circadian system. These are all specific scenarios that we are looking into and expanding the science on, and it’s really only the beginning.
SELF: We're always told that you should go to bed and wake up as close to the same time every day as possible. But that can feel unrealistic when you really want to sleep in on the weekends. In your professional opinion, how important is this really?
Dr. Peters: I have to be honest, I really do think it’s important. Sleep is something we are increasingly recognizing as a pillar of health. It should be prioritized. We should respect it. People can sleep normally if they can allow themselves to abide by their circadian rhythm and sleep during their preferred time.
If it’s dark and you’re feeling tired, you should take that as a signal that it’s time to go to bed and not fight it by staying up and watching Netflix. Think about it as a night owl, when you have to get up certain days for an early appointment: You don’t feel alert. You don’t feel your best. When other life demands throw you off your schedule, or you allow for interruptions and changes to your routine, then you start to experience the effects of sleep deprivation.
SELF: So you’re saying people should really try to make an effort not to sleep in until 11 A.M. on Saturday if they typically get up at 6 A.M. for work, even if our bodies might seem like they’re craving that?
Dr. Peters: It would be best to keep a regular schedule through the week. What happens is people wake up at 6 A.M. during the week for work, and they don’t get to bed as early as they need to, so they become sleep deprived. So, they sleep in on weekends. Sleeping in an extra hour probably isn’t too detrimental, and two hours, sure it’s OK, but it’s still not ideal. More than that and you can interrupt your circadian rhythm. If you think about it, sleeping in for a few hours extra on the weekend is like taking a trip across the country for a few days. It causes a variant of jet lag. Try to stay within an hour of your normal sleep and wake times on weekends too.
And it’s interesting that you say, “even if your body craves that.” If it really feels so painful to get up close to your normal work alarm time on weekends too, that’s a possible sign that you are experiencing some level of sleep deprivation, and it’s worth looking at your workweek sleep habits. If you are observing good sleep habits, waking up at your normal time or within an hour of it probably won’t be as difficult as you think. If it is, you may not be getting an adequate amount of sleep during the week to meet your sleep needs.