Males and Females Have Different Circadian Rhythms, Study Finds

If you have trouble syncing up your sleep schedule with your partner, there might be a scientific explanation for it. A team of researchers found that a person’s sex substantially impacts whether they’re a morning or night person, and how well they can adapt to disruptions in their normal sleep rhythm, like shift work and long-distance travel. 

The researchers who worked on the paper, which was published on September 4 in the journal Science, analyzed multiple studies on sleep patterns and wakefulness. They discovered that females tend to be morning people, and are more active during the day, while males are more likely to be active at night. Females were also better at coping with disruptions in their normal circadian rhythm than males, making them more resilient when disturbed during sleep. Males, on the other hand, are more likely to nap in the afternoon.

The researchers didn’t find any reasons for this sex difference in circadian rhythms, a phenomenon known as dimorphism. They don't know the exact cause yet, lead study author Seán T. Anderson, PhD, a post-doctoral fellow at the University of Pennsylvania, tells Verywell. However, he has a theory.

“One possible reason is that, historically, women have had a greater role in nurturing offspring,” Anderson says. “These earlier rhythms may have helped them to be more in sync with young children who are also more morning-oriented. Women also tend to sleep more deeply and are more resilient to nocturnal disturbances, which aligns with this idea.”

Researchers also found that this phenomenon isn't unique to humans. “We see a similar pattern across other species, which indicates that this dimorphism is not simply due to recent societal pressures but may have had an evolutionary cause,” Anderson says.

What Is a Circadian Rhythm?

Circadian rhythms are 24-hour cycles within the body’s internal clock, according to the National Institute of General Medical Sciences (NIGMS). These rhythms cause physical, mental, and behavioral changes on a daily cycle and they mostly respond to light and darkness in your environment. Your sleep-wake cycle is an example of a light-related circadian rhythm.

Most living things have circadian rhythms, including animals, plants, and microbes, the NIGMS says. Natural factors in the body produce these rhythms, but signals from the environment also affect them. Their main cue is daylight, which can turn on or off genes that control the molecular structure of biological clocks.

How to Sync Up Circadian Rhythms

Recent findings on sex differences in circadian rhythms are important for understanding why people behave the way they do at certain times of day, W. Christopher Winter, MD, board-certified sleep medicine researcher at Charlottesville Neurology and Sleep Medicine and author, tells Verywell.

“There are interesting patterns that emerge. For example, when women are on, they’re really on," Winter says, explaining women have a strong ability to focus. "But when their circadian rhythm drops, they’re not.”

But differences in circadian rhythms can create opposing patterns for couples of different sexes. “Your preference for mornings or evenings is wired into your biology, and it’s very difficult to change this in a meaningful, lasting way,” Anderson says. He recommends viewing differing circadian rhythms as a positive instead of a negative.

“If you find yourself awake in the early morning or late at night while your partner is sleeping, then this could be the perfect time to enjoy your own activities that they might not be interested in,” he says.

If you’re struggling to be able to find time together where you’re both awake and mentally present, Winter recommends trying to take small steps toward becoming more in sync. “You don’t need to say, ‘He’s a night person, she’s a morning person, and there’s nothing we can do about it,’” he says.

Winter suggests that the night owl in your relationship try to become more active in the morning by doing activities like exercising early. At the same time, the morning person could attempt to be livelier in the evening. “Over time, you may be more alert a little later or earlier, depending on what you're going for,” he says.

Male and female body clocks also tend to become more similar as they age. 

“So, once you get close to retirement age, your clocks may start to line up more harmoniously,” he says.