A new study published this week in the Proceedings of the National Academy of Sciences challenges that notion and puts forth a different theory: That that "high" it could be due to different substance called endocannabinoids.
Endocannabinoids can basically be thought of as the body's self-produced marijuana and, like cannabis, can impact a wide range of physiological processes, including appetite, pain, memory and mood.
Now the new research was only in mice, so it's unclear how it will apply to humans, but what the researchers found is almost certainly intriguing enough to inspire followup studies.
Researchers from the Central Institute of Mental Health of the University of Heidelberg took mice and gave them running wheels. They found that after the runs, the mice were less anxious and tolerated pain better.
Then they used drugs to block the animals’ endocannabinoid system. The results were striking. The animals were as anxious after running as before running and more sensitive to pain.
"We thus show for the first time to our knowledge that cannabinoid receptors are crucial for main aspects of a runner’s high," the researchers wrote.
There's been a lot of other interesting research on the subject of runner's high recently. In August, scientists at the University of Montreal published their work on a different animal study involving the hormone leptin, which is nicknamed the "satiety hormone."
Leptin, which regulates energy stores, signals to the body when it has enough fuel and energy. The researchers said it's possible that when you are in the middle of a workout, your leptin levels may fall, and this could "send a hunger signal to the brain's pleasure center to generate the rewarding effects of running."
In a study published in the journal Cell Metabolism, they compared normal mice with genetically engineered mice that lacked a leptin-sensitive protein called STAT3 that relays the leptin signal to release the reward chemical dopamine. The normal mice logged an average of six kilometers a day on a running wheel. But the genetically engineered mice ran nearly twice as much as the normal mice — 11 kilometers — each day.
If these studies are confirmed, the big question out there is whether these beneficial effects one day be bottled to help people exercise more to improve their health. It's looking more and more like a possibility.
This post has been updated.
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