Robert Waldinger, director of the Harvard Study of Adult Development, oversees the longest in-depth study of physical and mental well-being among adults. It has tracked hundreds of young adults from 1938 into their 80s. In an interview in the Harvard Gazette , Waldinger reported that satisfaction in relationships, particularly in marriages , was the best predictor of a happy and healthy life. He went on to say that the best data-backed hypothesis suggests that our relationships help us regulate stress. What he calls “social fitness” is as important as physical fitness and well-being when it comes to longevity. Waldinger also points out that new relationships can start at any age, as our social life is a living system that relies on maintenance and ongoing cultivation. People at 70, 80, or older can make new friends of all ages. And in the future of the 100-year life, a new friendship at 70 could last thirty years.…