Athletes have long basked in the happy glow that follows a good workout. Now, a new study suggests where those good feelings come from: Exercise boosts levels of phenylethylamine, a mood-elevating neuromodulator.
Many researchers believe that, in addition to the short-term feeling of well-being known as "runner's high," physical activity has significant, longer-lasting antidepressant effects. But a recent review questioned the evidence for that theory, and scientists have struggled to pin down the brain chemicals that explain how exercise might relieve depression. Some proposed endogenous opiates such as endorphins might be at work. But that theory was undermined by studies showing that opiate blockers did not dampen the good mood of the physically active.
The new study examined phenylethylamine, a molecule the brain uses to regulate the neurotransmitters dopamine and norepinephrine, and is sometimes prescribed for depression when other drugs fail. Ellen Billett and colleagues at Nottingham Trent University in the United Kingdom asked 20 healthy students to abstain from exercise for 24 hours, then run for 30 minutes on a treadmill. In 18 of the subjects, urine levels of phenylacetic acid--a reliable indicator of brain phenylethylamine--rose after exercise, the scientists report in the October issue of the British Journal of Sports Medicine. The finding represents an important first step in linking exercise and mood, Billett says, and may bolster the British government's decision in April to recommend that doctors prescribe exercise to alleviate depression.
Still, scientists have yet to validate that the effects of physical exercise continue over time, and that phenylethylamine directly improves mood, says Andrew Steptoe, a psychologist at University College in London. Vigorous exercise may produce a whole series of changes in the body that promote well-being, says Steptoe, of which a phenylethylamine boost could be just one aspect.