Not everyone’s circadian rhythm is a flat 24 hours. Yours could be 23 or 25. Some body clocks operate on a much shorter 20-hour cycle. This explains why some people are night owls, others are early birds, and a few of us feel permanently jet-lagged.
It turns out there’s a genetic explanation.
Everyone has a central clock that tells all the individual clocks within their body (the one in your muscles, liver, stomach, etc.) what time it is based on Earth’s 24-hour cycle and how to act accordingly. Each of those clocks are regulated by clock proteins, including a major one called the PER protein. When that protein is out of sync, it can throw you into a common 23-hour clock rhythm or an even more common 25-hour clock rhythm. Researchers at universities including the University of California Santa Cruz (UCSC) recently discovered that people with certain genetic mutations in an enzyme (called casein kinase 1) can even be thrown into a 20-hour clock rhythm.
Even though people on these schedules often still get the ideal seven or more hours of sleep, a disrupted circadian rhythm—or living out of tune with the Earth’s day and night—has been linked to a host of health issues. The thinking? Your clock will try very hard to align to the Earth on its own, but if yours is that much shorter, you can never really catch up, creating disarray on a molecular level. “It’s like living with perpetual jet lag,” says Carrie Partch, PhD, an Associate Professor in the Department of Chemistry and Biochemistry at UCSC and the study’s lead author.
The good news is that scientists believe this gene variant that makes people run on a 20-hour clock is rare (like, one in a million). Only people who go to bed around 7 pm and wake up around 4 am, even on weekends, likely have it. It’s a variation you’re born with and one that can affect your sleep cycle even as a child, though you might not notice until your teens or later, when you have more control over your bedtime.
“Your lifestyle—particularly when you train and when you eat—can be modified to shift the phase, or time settings, of your body clocks to peak earlier or later in the day depending on your goal.”
Karyn Esser, PhD, Professor and Associate Program Director at the University of Florida’s Institute of Myology
“Having a dramatically shorter clock means your melatonin release, which prompts your body for sleep, peaks much earlier, so you’re tired well before you should be,” says Partch. “Then you wake up before the day has really started.”
Whether your clock’s short or long, you don’t have to let it dictate how you tick and tock. “Your lifestyle—particularly when you train and when you eat—can be modified to shift the phase, or time settings, of your body clocks to peak earlier or later in the day depending on your goal,” says Karyn Esser, PhD, a Professor and Associate Program Director at the University of Florida’s Institute of Myology and a leading researcher on the relationship between circadian rhythms and skeletal muscle.
Research on body clocks and training is still in progress. But if you feel wiped by, say, 8 pm, you would probably benefit most from an afternoon workout. That’s because exercise can shift your body clocks, which can delay the onset of melatonin, says Esser. If you struggle to get to sleep before midnight, a morning session—preferably an outdoor one—should align your circadian cues for sleep onset to peak earlier in the day. “The nice thing is that your muscle clocks are very responsive to exercise and can adjust to the training schedule you set forth, so your muscles will get used to any scheduling changes,” she says. “As they do, they’ll perform better, so you should eventually see similar, if not greater, results.”
Regardless of your personal clock, you also want to eat breakfast, lunch, and dinner within a 10-hour time frame that best matches the hours of sunlight, adds Partch. Exposing yourself to natural light as soon as you wake and limiting blue-light screens (your phone, TV, and laptop) after dark to minimize melatonin disruption helps too.
“There’s so much more to learn, but it’s fascinating to know that we all operate on our own clock, which controls practically everything in our bodies,” says Partch. The closer you pay attention to yours, the more likely you’ll feel more control over when you wake, eat, train, sleep—whatever it is you want to do with your time.