What's Really Behind Runner's High

Leptin hormone tied to mid-run euphoria


The hormone that helps you feel full may also help you enjoy your morning run a little more.

A new study from Canada found that low levels of leptin (a hormone found in the body's fat cells) may be instrumental in inducing euphoric feelings in the middle of a run — sometimes known as a "runner's high."

So far, research has only been conducted on mice.

Leptin informs the body that it has enough energy to survive. It also causes the lethargic feeling that sometimes follows a big meal.

Past research linked low levels of leptin to a desire to exercise more. According to researchers, this extra motivation may be a result of the mind giving the body a reason to engage in physical activity — which humans historically needed to do to look for food.

"Based on these findings, we think that a fall in leptin levels increases motivation for physical activity as a means to enhance exploration and the pursuit of food," said lead study author Stephanie Fulton, PhD, an associate professor of nutrition at the University of Montreal, in a press release. "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."

Dr. Fulton and team tested normal mice against mice lacking the leptin-inducing protein STAT3. STAT3 sends messages to the part of the brain that produces dopamine (a chemical that causes feelings of pleasure).

The normal mice ran 6 kilometers (about 3.7 miles) per day on average, while the STAT3-deficient mice ran 11 kilometers (about 7 miles). The STAT3-deficient mice also spent more time on the side of their cages associated with running than the normal mice did.

STAT3 deficiency was found to cause a blunted release of dopamine in the brain, which has been linked to pleasure-seeking and risky behavior in humans.

This may mean that the STAT3-deficient mice were looking for "high" to release the dopamine that their low leptin levels couldn't.

Dr. Fulton and team plan to test the relationship between dopamine and stamina next.

This study was published Sept. 1 in the journal Cell Metabolism.

The Canadian Institutes of Health Research, Fonds de Recherche en Sante de Quebec, the Canadian Diabetes Association and Universite de Montreal funded this research. No conflicts of interest were disclosed.