Night owl or early bird? Here's how your inner clock impacts your health
Did the holidays mess up your sleep patterns? Maybe you stayed up late ringing in the new year, or changed time zones while traveling. Science journalist Lynne Peeples says the body's circadian rhythms are sensitive to many different types of changes — but especially to sunlight.
In her new book, The Inner Clock: Living in Sync with Our Circadian Rhythms, Peeples describes an experiment in which she lived for 10 days in an underground bunker, with no exposure to sunlight or clocks.
"I wanted to get a sense of my personal rhythm," she explains. "We all tick a little differently, and so I wasn't totally clear on just how my inner clocks ticked."
Peeples says she quickly lost sense of time, and began suffering from clumsiness and brain fog: "I think day seven or eight, I was just dropping everything and super uncoordinated."
Throughout the experiment, Peeples charted her temperature, heart rate and glucose levels. Later, she worked with scientists to analyze the data she had gathered over the 10-day period.
"About that same time that I was feeling just really out of whack, uncoordinated and a little loopy ... that was when the data showed that my heart-rate rhythm and my temperature rhythms were no longer coordinated, and also when I was becoming more and more uncoordinated with the sun," she says.
Peeples says her time in the bunker illustrates the importance of daylight: "Our clocks and this coordination of our entire physiology really counts on those inputs of light and dark to tell the body that it's day and night and coordinate those activities. And when we don't get daylight, when we don't get those photons to help calibrate those clocks, then things go awry. And that affects our mental health and our physical health."
Interview highlights
On how important circadian rhythms are to our overall health.
We have trillions of tiny "clocks" in our bodies. Really, when you think about it, nearly every cell in your body has a clock. And these clocks evolved to coordinate with each other and with the sun to help our bodies be primed to do the right things at the right time. … We evolved to be most alert and awake and take advantage of the light of the day.
And "circa" in circadian means about or around. So our inner clocks did evolve to be ... around 24 hours but they're not precise timekeepers so we need that regular calibration from the environment, from the Earth's 24-hour cycle to keep them coordinated with each other and with the sun so that they are primed to do those right things at the right times.
On the importance of daylight
The science suggests that light across the whole day is crucial, but in particular, morning light. … It's pretty clear that during the daytime, especially in the early hours, getting daylight will help recalibrate our rhythms. And then throughout the day, the accumulation of that, getting those photons from the full spectrum that the sun offers, in particular those blue wavelengths of light that we get from the sun, will help align our rhythms as well as help make them more robust. ...
Then at night again, to keep that contrast, to make the body understand that this was day and this is night when we're supposed to wind down for sleep, that's when we need the lights down and not blasting our overhead lights in our our homes, for example, or putting our face in front of screens. So it's all about that contrast.
On daylight saving time disrupting our circadian rhythms
When we spring forward or fall back, we are giving ourselves a dose of jet lag, but we're locking the clock there. So when we spring forward, we're essentially stealing an hour of light from the morning, which is when we really want the light. And we're tagging that on to the end of the day, when we our bodies really are looking for the dark and it's throwing us out of alignment from the sun. Before we had any kind of standard time around the world locally, the sun was generally at its highest point of overhead at noon. And if we shift that with daylight saving time, we're throwing that off.
On everyone's clocks ticking differently
We all tick a little differently. Those inner clocks in our bodies that tick at around 24 hours, for some of us, that means that they take a little longer than 24 hours, and for some, they're faster and it's a little under 24 hours to do its full circuit, so to speak. So because of that, there's times a day that we have a greater predilection for certain things. And if we think about sleep/wake, that's where I think most of us experience these differences.
There are some of us that if we have a shorter circadian rhythm, we might more likely be early birds. It's easier for us to go to sleep early at night and we might wake early. And on the other end of the spectrum, there are the extreme night owls, where they may be at their peak late and be awake and alert into the night and then wanting to sleep in late in the morning.
So it's both the speed at which our clocks tick, as well as this alignment with light. Scientists are trying to understand that more now. But how our body responds to light is also affecting how these clocks align with the 24-hour day. There's not just early birds and night owls. There's a full spectrum that goes to pretty great extremes. Different genetics can program or predispose some people to truly function better overnight than during the day.
On how our clock changes with age
When we are first born, as parents can attest, we don't really have a lot of rhythm. We're kind of eating and sleeping throughout the day and night. And then as we get a little older, young kids tend to be early risers, and that quickly changes when we reach adolescence. So at that point, early teen years, our rhythms start to drift later., [by] as much as two or three hours. A kid that used to rise and be alert and ready to go at 6 a.m., now it might be more like 9 a.m. And of course, that means it's harder for these kids to go to sleep at night. And then as we get older, it kind of balances out a little bit.
And then in our older years, on average, we tend to be maybe slightly early risers. But ... scientists are finding, as we get older, our circadian rhythms get blunted, they get weaker. So we do not have as profound of a rise and fall in our rhythms and that manifests in a weaker sleep/wake cycle. So we might be more prone to napping during the day. You know, you think about like the the grandparent sitting in the chair and are falling asleep during the day and then maybe struggling to sleep at night. That is always partially due to the circadian rhythm being weakened as we get older. But ... we're also understanding how to potentially strengthen those rhythms, in part through things like getting that extra contrast of light and dark throughout the day.
On research out of the University of Pittsburgh studying the correlation between some mental health disorders and circadian rhythms
It might be the case that certain drugs that are used for mental health disorders, like schizophrenia and depression, might actually work by affecting the circadian clock. … This vicious spiral that happens with a lot of mental health disorders where somebody has depression, for example, and they're indoors during the day. … Being indoors and missing that morning light then sets them up to more likely stay awake later at night. And then that's going to set them up to sleep in the next day. And overall, that's going to weaken their rhythms. And if there's a link between that and the disorder itself, it creates the snowball effect that some of the science is pointing to potentially a way out.
On disruption to our circadian rhythms and Alzheimer's
The science is pretty clear that as we disrupt our rhythms and we disrupt our immune system and our ability to metabolize food at the right times a day and all these things. It's not a shock to scientists that there could be ramifications for how that could propel the development of cancer and heart disease, other cardiometabolic disorders, and then in the long term, potentially dementia. …
If we understand that, maybe that could help us find new treatments or help certain people as we get older to access more of those cues, more of that circadian hygiene that helps their rhythms stay robust. And could that again put off and delay the onset of these diseases? Or if somebody has that disease, could having those stronger rhythms alleviate some of the symptoms and slow down the progression of that disease? These are open questions, but a lot of promising research [is] suggesting that there there is a lot of potential here.
Sam Briger and Anna Bauman produced and edited this interview for broadcast. Bridget Bentz, Molly Seavy-Nesper and Carmel Wroth adapted it for the web.
