The downside of staying up late

Night owls take more risks with their health than early birds. We probably always knew that but now we know what and why.

During his time in the Oval Office, Barack Obama was a self-proclaimed “night guy” who tended to stay up well past midnight despite his early morning duties.

His predecessor, George W. Bush, was usually in bed by 10 and often started his workday well before seven a.m.

New research suggests Bush and other early birds may have fewer health risks than their night owl counterparts.

Last year, a study found people who considered themselves to be evening types, loosely defined as those who prefer to stay up and rise late, were at greater risk than morning types for psychological disorders, diabetes, neurological disorders, gut disorders, and heart disease.

And a study published recently in The BMJ medical journal found that in women, being a morning person can lower the risk of breast cancer. The study team analyzed genetic data, sleep questionnaires, and breast cancer incidence reports collected from hundreds of thousands of women. Using a variety of analytic techniques, they found consistent evidence that women who were early to rise and early to bed were less likely to develop breast cancer than women who stayed up and slept in late.

The study authors acknowledged that the findings had limitations; for example, the women in the study self-reported their sleep-wake habits and preferences, so were subject to error. But their study’s findings aren’t the first to link morning preferences with a health benefit.

For some time, researchers have understood that human beings are equipped with built-in clock genes that exist in every cell in the body, and are active or inactive at regular intervals throughout the day. These clock genes, in conjunction with environmental cues such as daytime sun exposure, help set the body’s internal circadian rhythms or schedules, which regulate a person’s appetite, hormone levels, body temperature, energy, sleep schedule and 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.

Wulff says the body’s internal clocks do not exactly overlap with the external, 24-hour clock set by our solar system. This is by design. “It gives us the flexibility to adapt or adjust to different environments, such as seasonal shifts in daylight schedules.”

Most people have overlap between their internal clocks and the external world’s 24-hour clock. They may run slightly ahead or behind, and so their preference for rising on the early side or staying up a bit later isn’t too dramatic.

But in up to 10% of the population, there’s a sizeable discrepancy. This discrepancy creates an extreme preference for morningness or eveningness, she says. And the underlying genetic variations that account for this extreme preference for eveningness seem to be associated with a greater risk for health issues.


One possibility is that the clock genes that are associated with night owl status also increase a person’s risk for various health issues.  Another  is that work or school or social demands are more likely to impose unnatural sleep-wake schedules on evening types, as opposed to morning people.

The resulting disconnect 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 promote poor sleep, unhealthy hormone shifts, metabolic issues, or other biological changes that could lead to things like 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, microbiome and the heart, everything will be affected.”

This only applies to the small percentage of night owls who are at the extreme end of the spectrum.  Most people, those who get up between 5 and 9 a.m. and go to bed between 10 p.m. and one in the morning, probably have little to worry about.

For extreme night owls, they need to get to bed earlier. Just as shift workers who are forced to sleep during the day and work all night are at higher risk for cancer and other health problems, extreme night owls who are forced to rise early in the morning may run into issues.

If there’s some way for them to adjust their obligations to suit their sleep-wake preferences, their health may benefit from it.