According to a new study regular exercise may help to safeguard the mind against depression through previously unknown effects on working muscles. Mental health experts have long been aware that exercise somehow makes people and animals emotionally more positive, but precisely how physical activity can enhance someone’s mental state has been a mystery.

Researchers at the Karolinska Institute in Stockholm knew from earlier research that aerobic exercise, in both mice and people, increases the production within muscles of an enzyme called PGC-1alpha1 (PGC). In studies using mice they found that this enzyme protects the brain from a substance called kynurenine which accumulates in the bloodstream after stress. Kynurenine is able to pass the blood-brain barrier, and once inside the brain it creates inflammation that is thought to cause depression.

Exercise elevates the body’s level of PGC, and this breaks down the kynurenine so that it cannot pass the blood-brain barrier. Thus the brain is protected from the inflammation and depression that is caused by stress. Maria Lindskog, a co-author of the study, summarises the results this way: “you reduce the risk of getting depression when you exercise”. So if work and other pressures are getting you down, it may be a good idea to go for a jog... just keep your kynurenine in check.