New research in The Journal of Physiology suggests that exercising at certain times of the day can alter the circadian rhythms, potentially offering a new therapy for jet lag and shift work.

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Jet lag can lead to insomnia and fatigue, but exercise may help alleviate such disruptions to a person’s body clock.

Circadian rhythms, which are “physical, mental, and behavioral changes that follow a daily cycle,” regulate our bodies.

Light and darkness are the main factors that affect our circadian rhythms.

A cluster of nerve cells in the brain receives information about the amount of light through the optic nerves, “telling” our brains to make us sleepy by releasing the sleep hormone melatonin.

However, when we travel to a different time zone or work the night shift, we disrupt these circadian rhythms. Some of the adverse effects of such disruptions include insomnia and fatigue, trouble focusing, headaches, and gastrointestinal problems.

There are currently no treatments for the adverse effects of jet lag or shift work, so researchers are trying to devise novel therapies. For instance, one recent study has found that the retina contains some cells that secrete vasopressin, another hormone that helps regulate circadian rhythms.

Altering the vasopressin signaling pathway may one day lead to the manufacture of eye drops that could offset the effects of jet lag, but such treatments are still far from becoming a reality.

However, what if it was possible to treat jet lag without drugs? What if light was not the only factor that affects circadian rhythms?

Shawn Youngstedt, from the College of Nursing and Health Innovation and the College of Health Solutions at Arizona State University in Phoenix, and his colleagues asked themselves these questions.

Their research found that exercise may counter the negative effects of circadian rhythm disruption.

Youngstedt and his colleagues examined the effects of exercise on 51 “aerobically fit” participants aged 59–75 years and 48 study participants aged 18–30 years. They measured the participants’ circadian rhythms and how exercise affected them for a period of 5.5 days. Specifically, the 99 volunteers all did 1 hour of moderate treadmill exercise for 3 consecutive days at one of eight different times during the day or night.

The scientists determined the participants’ baseline body clock by analyzing their urine samples and determining their levels of melatonin.

The body releases melatonin in different amounts at different times of the day: The hormone peaks in the evening and drops in the morning. By taking samples from the volunteers every 90 minutes, the researchers identified the precise time when their melatonin rose and fell throughout the day.

Exercising at 7 a.m. or between 1 p.m. and 4 p.m. shifted the circadian rhythm to an earlier time, while engaging in exercise between 7 p.m. and 10 p.m. pushed the body clock back. Age or sex did not affect these results.

On the other hand, exercising between 1 a.m. and 4 a.m. or at 10 a.m. did not affect their melatonin levels.

Youngstedt comments on the findings, saying: “Exercise has been known to cause changes to our body clock. We were able to clearly show in this study when exercise delays the body clock and when it advances it.”

“This is the first study to compare exercise’s effects on the body clock, and could open up the possibility of using exercise to help counter the negative effects of jet lag and shift work.”

Shawn Youngstedt

However, the study authors caution that because the participants had higher fitness levels than the general population, the results may not extend to people who are less fit.