“The study by Perreau-Linck and colleagues36 is the first to report that self-induced changes in mood can influence serotonin synthesis. […]
Exposure to bright light is a second possible approach to increasing serotonin without drugs. […]
Several lines of research suggest that exercise increases brain serotonin function in the human brain. […]
The fourth factor that could play a role in raising brain serotonin is diet. According to some evidence, tryptophan, which increases brain serotonin in humans as in experimental animals,69 is an effective antidepressant in mild-to-moderate depression.”
Young, Simon (2007). Journal of Psychiatry & Neuroscience.
2007 November; 32(6): 394–399.