July 12, 2026
I'd like to share a thought-provoking article from the online publication Medium. It explores whether being a morning lark or a night owl affects your health. It caught my eye because of a recent finding linking a “morning person” tendency with a lower risk of breast cancer.
New research suggests “morning larks” may have fewer health risks than their “night owl” counterparts.
Last year, a study found that people who identified as “evening types” — broadly, those who prefer to stay up late and wake late — faced higher risks than morning types for psychological disorders, diabetes, neurological disorders, gut disorders, and even death. Additional research along these lines also indicates that evening types carry a greater risk of heart disease.
And a study published last week in The BMJ medical journal found that among women, being a “morning person” is linked to a lower risk of breast cancer. The U.K. research team examined genetic data, sleep questionnaires, and breast cancer incidence reports gathered from hundreds of thousands of women. Applying several analytic methods, they found “consistent evidence” that women who rose early and went to bed early were less likely to develop breast cancer than those who stayed up and slept in.
The study authors acknowledged limitations in their findings — most notably that the women self-reported their sleep-wake habits and preferences, which can introduce error. Still, their results are not the first to connect morning tendencies with a health advantage.
For some time, researchers have known that humans carry built-in “clock genes” in every cell of the body, switching on and off at regular intervals across the day. Together with environmental cues such as daytime sunlight, these clock genes help establish the body's internal circadian rhythms — the schedules that govern appetite, hormone levels, body temperature, energy, sleep timing, and much more.
“The reason for this is our planet is ruled by the solar system which generates a rhythmic environment, and over millions of years organisms have developed these clocks to cope with the environmental rhythms,” says Katharina Wulff, a chronobiologist and senior lecturer in molecular biology at Umeå University in Sweden.
Yet Wulff notes that the body's internal clocks don't perfectly align with the external 24-hour clock set by our solar system — and that's intentional. “This allows us the flexibility to adapt or adjust to different environments, such as seasonal shifts in daylight schedules,” she explains.
For most people, there's substantial overlap between their internal clocks and the external world's 24-hour clock. They may run slightly ahead or behind, so their preference for rising early or staying up a bit later isn't very pronounced. But in some — up to 10% of the population, Wulff estimates — there's a notable mismatch. That mismatch produces an extreme preference for morningness or eveningness, she says. And the genetic variations behind an extreme evening preference appear to be tied to a higher risk of health problems.
But why? One possibility is that the clock genes linked to night owl status also raise a person's risk for various health issues. Another possibility is that work, school, or social demands more often impose unnatural sleep-wake schedules on evening types than on morning people. The resulting gap between when a night owl's body wants to sleep and wake and when life forces them to sleep and wake may disrupt their natural internal rhythms in ways that foster poor sleep, unhealthy hormone shifts, metabolic problems, or other biological changes that could lead to conditions such as cancer or depression.
“If people are always having to adhere to a schedule they're not suited to, that may create health problems,” Wulff says. “The muscles and microbiome and eating and the heart — everything will be affected.” Wulff adds that this applies only to the small share of night owls at the extreme end of the spectrum. If you're like most people — meaning you tend to get up between 5 and 9 a.m. and go to bed between 10 p.m. and one in the morning — you likely have little to worry about.
For extreme night owls, the takeaway from these studies isn't that they should go to bed earlier; rather, they'd be better off if allowed to follow their body's natural inclination to stay up and sleep a bit later, says Wulff. Just as shift workers forced to sleep during the day and work all night face higher risks of cancer and other health problems, extreme night owls forced to rise early may run into issues. If they can adjust their obligations to match their sleep-wake preferences, their health may benefit.
I'm Dr. Michael Hunter. I hope your day is filled with joy!
I earned my undergraduate degree from Harvard, my medical degree from Yale, and completed a radiation oncology residency at the University of Pennsylvania. I've been honored to be named a “top doctor” in Seattle Magazine, US News & World Report, Seattle Metropolitan Magazine, 425 Magazine, and WA magazine. Readers of the Kirkland Advertiser have voted me the top doctor (in any field) in the region on multiple occasions. I care for people with cancer at Evergreen Hospital, just outside Seattle. And now the small print: Nothing here is meant as individualized advice, and I encourage you to consult a trusted health care provider. Thank you for joining me today.
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