Early to Wake, and to Walk

Compared with people who tend to stay up late, early risers did the equivalent of 20 to 30 minutes more walking each day.

evening types go to bed later and wake up later than morning types. They also tend to move around far less throughout the day, according to one of the first studies to track daily movements of a large sample of early birds and night owls. It suggests that knowing our chronotype might be important for our health.

Each of us contains a master internal body clock, located in our brains, that tracks and absorbs outside clues, such as ambient light, to determine what time it is and how our bodies should react. This master clock directs the release of hormones, such as melatonin, and other chemicals that affect sleep, wakefulness, hunger and other physiological systems.

Responding to these biochemical signals, as well as genetic inclinations and other factors, we each develop a chronotype, our biological response to the passage of time. Research shows that most people harbor a morning or day chronotype when young, an evening version in adolescence and young adulthood, and a return to a day or morning type by middle age. But some people remain lifelong night owls.

In past studies, people identified as evening types were more likely to develop

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heart disease, obesity, diabetes and other metabolic conditions. They also tended to exercise less and sit far more.

But these studies depended on people’s recollections, which are notoriously unreliable. For the new study, published in the Scandinavian Journal of Medicine & Science in Sports, almost 6,000 Finns visited researchers at the University of Oulu for an in-person exam and a variety of questionnaires, including one designed to determine their chronotypes.

The researchers also gave the volunteers an activity tracker to wear for two weeks. They found that among men and women, the day types moved more than the evening types.

This study does not explain why evening types tend to be less active, said Laura Nauha, who led the study. There may be physiological interactions between body clocks, muscles and other bodily systems. But practical considerations probably play a larger part, she says.

Evening types may feel most energetic at night, when gyms could be closed and pathways dark. Another obvious factor “could be lack of sleep.”

Ms. Nauha says the findings suggest that night owls “may need to work harder to try to ensure they exercise.”