According to studies, the chemical serotonin makes a person happier, calmer, and more focused. Low serotonin levels are often found in people with depression and other mental health disorders, but it is unclear whether low serotonin levels cause depression, if depression actually lowers serotonin, or if there are other factors.

Many antidepressant medications, known as selective serotonin reuptake inhibitors (SSRIs), target the body's serotonin levels to treat depression, post-traumatic stress disorder, anxiety, and some eating disorders. SRRI medications prevent nerve cells from absorbing serotonin, so it can travel elsewhere in the body.

Serotonin increases the rate of digestion, helps propel harmful pathogens through your system more quickly, and aids in appetite control. However, serotonin also plays a role in gut inflammation, and people with intestinal problems tend to have overactive serotonin, which causes unpleasant symptoms.

Exercise increases serotonin levels by releasing an amino acid called tryptophan in the body, which turns into serotonin in the brain. Aerobic exercise such as running, cycling, or swimming are more effective than anaerobic exercise to level the body's tryptophan content and maximize serotonin from a workout.

People living in colder, darker climates can suffer from the seasonal affective disorder (SAD), and the drop in mood during winter could be due to low serotonin levels. However, this is reversible, and many people find that 45 minutes of light therapy daily is enough to help regulate their mood and fight off SAD.