George Vaillant conducted a thirty-year study of a group of Harvard graduates that found that adopting an altruistic lifestyle is a critical component of good mental health. David McClelland, a psychologist at Harvard, showed a group of students a film of Mother Teresa working with the poor and sick in India. After he analyzed their saliva and found increased immunoglobulin-A, an antibody that helps fight respiratory infections.
Volunteering decreases the risk of depression, gives a sense of meaning and purpose, improves social connectedness, and even extends life expectancy!
So service is good for our mental and physical health.