The Harvard Study of Adult Development is the longest and most comprehensive investigation of the aging process ever conducted. Since the 1930s, researchers have closely followed more than 800 men and women from adolescence to old age to seek clues about behaviors and activities that are associated with healthy longevity. Some of the findings surprised George Vaillant, a former director of this project and author of Aging Well. He anticipated that “the longevity of your parents, the quality of your childhood and cholesterol levels would be very influential.” They were not. Keeping mentally active and having lots of friends were much more important. A happy marriage or good long-termrelationship at age 50 was a leading indicator of being healthy at age 80 whereas a low cholesterol level had very little significance.

Why would a happy marriage or having lots of friends promote healthy aging? Stress can accelerate the aging process, however, having strong social and emotional support from friends or family can reduce the harmful effects of stress. Stress contributes to illness and premature mortality and reducesthe immune system’s ability to ward off infections and certain cancers. British researchers reported that in a study of more than 180 senior citizens who received the influenza vaccine, those who were happily married developed higher antibodies, and participants who had experienced a significant bereavement had poorer antibody responses.