If you’re a runner, you’ve probably experienced the “runner’s high.”
That’s the euphoric feeling generally considered responsible for giving runners an extra boost.
According to a new study in Cell Metabolism this feeling is controlled partially by a hormone called leptin.
The less leptin you have, the more likely you are to experience runner’s high.
In a study on mice, those with reduced leptin in the brain logged about twice as many miles on a running wheel compared to normal mice.
According to the findings, decreased leptin levels increase motivation for physical activity in order to pursue food.
“Our study also suggests that people with lower fat-adjusted leptin levels, such as high-performance marathon runners, could potentially be more susceptible to the rewarding effects of running and thus possibly more inclined to exercise,” said study author Stephanie Fulton, Ph.D., associate professor of nutrition at the University of Montreal, in a statement.
What Is Leptin?
Leptin is a hormone derived from fat cells that sends a signal to the brain when the body is full on fuel and energy.
In the past, having low levels of leptin was linked to exercise addiction and fast marathon times in humans. In mice, it has been linked to faster running speeds and duration.
Fulton’s research team examined genetically engineered mice that were lacking STAT3, a leptin-sensitive protein. STAT3 activates the leptin signal in neurons that release dopamine. Dopamine is a feel-good chemical.
The researchers observed that normal mice ran 6 kilometers per day on a running wheel while the mice deficient in STAT3 ran 11 kilometers a day.
The STAT3-deficient mice also spent more time in the side of the chamber that was associated with running than the normal mice.
Researchers concluded the findings suggest that a decline in leptin-induced STAT3 signaling increases the rewarding effects of running. STAT3 deficiency also led to impaired dopamine signaling, which has been tied to enhanced reward seeking in humans.
“Besides its effect on body weight regulation, leptin is also important for motivation to run. Lower leptin levels increase running performance and promotes the ‘runner’s high,’” Fulton told Healthline. “We have evolved to increase the return on effective food acquisition behaviors and leptin is sending the brain a clear message: When food is scarce, it’s fun to run to chase some down.”
The Anorexia Link
It’s believed that people with anorexia have low fat-adjusted leptin levels that are tied to increased restlessness and hyperactivity.
Fulton said the mechanism detailed in her work could explain the hyperactivity in anorexia patients.
She warned that people should be cautious when linking the study’s findings to anorexia because she is not aware of direct evidence that leptin therapy could reduce hyperactivity.
“Our findings are convincing and suggest that leptin might have great potential as a medication for treatment of anorexia-induced hyperactivity,” she said. “However, it’s important to keep in mind that leptin is an anorexigenic hormone, and if anorexic patients do not eat, leptin treatment could bring serious, dangerous consequences, including an earlier death.”
In the future, the researchers want to delve into the association between food seeking and runner’s reward.
They also want to look at the neural pathways of how dopamine contributes to the runner’s high, the possibility that it evolved to enhance stamina, and look at the increase in the probability of success these individuals have for foraging and hunting.
“We do not want people to think that leptin is the only metabolic signal controlling the rewarding effects of running. Likewise, dopamine is not the only brain chemical involved,” Fulton added.
So is the runner’s high a positive or negative thing?
Fulton said the short-term benefits are “unquestionable” but being addicted to running — or the high — could have harmful effects.
“Avid runners will need to get their daily fix of miles, devoting an increasing amount of hours per day to running exercise, solely to get their high. For these individuals, running exercise has an importance that may outweigh everything else in their lives, including work, friends, and family,” Fulton said.