The Study of Adult Development led for over 30 years by George Vaillant, a professor at Harvard Medical School, my alma mater, followed 800 people for their entire lives to see what actually makes people live happier, healthier, and longer.  The study was the longest prospective study of physical and mental health in the world, and it found six factors that impact happiness, including relationships, education, and generosity.

Source: 6 things that make people live longer, happier lives – Business Insider