How does exercise affect serotonin levels?

There are findings showing that exercise may boost serotonin levels in the brain, resulting in a calming, anxiety-reducing effect, and -- in some cases -- a drowsiness effect. In addition, a stable serotonin level in the brain is associated with a positive mood state or feeling good over a period of time. We know that women may have a greater sensitivity to the changes in serotonin, which is often indicated by mood swings during the menstrual cycle. Female hormones also act on the neurotransmitter serotonin following the birth of a child or during menopause. Lack of exercise and inactivity can aggravate low serotonin levels.  

Serotonin is a neurotransmitter found in the brain that aids in transporting messages throughout the nervous system. It is known to regulate mood, appetite, and the circadian rhythm. Exercise increases serotonin levels, and tryptophan levels in the brain. Tryptophan is required to produce serotonin. To achieve optimal serotonin levels, exercise is recommended 3 hours per week – or 30 minutes per day.