Exercise can alleviate mild depression, but exactly how it does so is unclear. Now Ellen Billett thinks she's found a key component in the process: a molecule called phenylethylamine, which can modulate levels of mood-altering serotonin and dopamine in the brain. Billett, a biochemist at Nottingham Trent University in England, began studying phenylethylamine because studies have shown it can be used to treat some forms of moderate depression. Other research, meanwhile, revealed the compound is scarce in the body fluids of depressed people. To test this connection, Billett asked 20 healthy men to refrain from exercise on one day and then run on a treadmill for 30 minutes the next. She took urine samples from the subjects on both days and discovered that the concentrations of phenylacetic acid, a breakdown product of phenylethylamine, increased by an average of 77 percent after exercise.
Phenylethylamine can cross from the bloodstream to the brain, so it could possibly help mediate the connection between exercise and mood in the body's peripheral tissues. The molecule is also chemically similar to amphetamine, a hint that it might be one source of runner's high. The latest findings may encourage a more holistic approach to psychiatry. "It gives doctors more reason to prescribe exercise as an alternative or an adjunct to drugs for treating mild to moderate depression," Billett says.