The Atlantic has a long, interesting article from 2009 covering the Grant Study; a research project at Harvard that has followed 268 men for over 72 years, making it one of the most comprehensive longitudinal studies in history. It has followed the subjects through “war, career, marriage and divorce, parenthood and grandparenthood, and old age.”

What can it teach us about living a good life?

What allows people to work, and love, as they grow old? By the time the Grant Study men had entered retirement, Vaillant, who had then been following them for a quarter century, had identified seven major factors that predict healthy aging, both physically and psychologically.

Employing mature adaptations was one. The others were education, stable marriage, not smoking, not abusing alcohol, some exercise, and healthy weight. Of the 106 Harvard men who had five or six of these factors in their favor at age 50, half ended up at 80 as what Vaillant called “happy-well” and only 7.5 percent as “sad-sick.” Meanwhile, of the men who had three or fewer of the health factors at age 50, none ended up “happy-well” at 80. Even if they had been in adequate physical shape at 50, the men who had three or fewer protective factors were three times as likely to be dead at 80 as those with four or more factors.

What factors don’t matter? Vaillant identified some surprises. Cholesterol levels at age 50 have nothing to do with health in old age. While social ease correlates highly with good psychosocial adjustment in college and early adulthood, its significance diminishes over time. The predictive importance of childhood temperament also diminishes over time: shy, anxious kids tend to do poorly in young adulthood, but by age 70, are just as likely as the outgoing kids to be “happy-well.” Vaillant sums up: “If you follow lives long enough, the risk factors for healthy life adjustment change. There is an age to watch your cholesterol and an age to ignore it.”

The study has yielded some additional subtle surprises. Regular exercise in college predicted late-life mental health better than it did physical health. And depression turned out to be a major drain on physical health: of the men who were diagnosed with depression by age 50, more than 70 percent had died or were chronically ill by 63. More broadly, pessimists seemed to suffer physically in comparison with optimists, perhaps because they’re less likely to connect with others or care for themselves.

More than 80 percent of the Grant Study men served in World War II, a fact that allowed Vaillant to study the effect of combat. The men who survived heavy fighting developed more chronic physical illnesses and died sooner than those who saw little or no combat, he found. And “severity of trauma is the best predictor of who is likely to develop PTSD.” (This may sound obvious, but it countered the claim that post-traumatic stress disorder was just the manifestation of preexisting troubles.) He also found that personality traits assigned by the psychiatrists in the initial interviews largely predicted who would become Democrats (descriptions included “sensitive,” “cultural,” and “introspective”) and Republicans (“pragmatic” and “organized”).

Again and again, Vaillant has returned to his major preoccupations. One is alcoholism, which he found is probably the horse, and not the cart, of pathology. “People often say, ‘That poor man. His wife left him and he’s taken to drink,’” Vaillant says. “But when you look closely, you see that he’s begun to drink, and that has helped drive his wife away.” The horrors of drink so preoccupied Vaillant that he devoted a stand-alone study to it: The Natural History of Alcoholism.

Vaillant’s other main interest is the power of relationships. “It is social aptitude,” he writes, “not intellectual brilliance or parental social class, that leads to successful aging.” Warm connections are necessary—and if not found in a mother or father, they can come from siblings, uncles, friends, mentors. The men’s relationships at age 47, he found, predicted late-life adjustment better than any other variable, except defenses. Good sibling relationships seem especially powerful: 93 percent of the men who were thriving at age 65 had been close to a brother or sister when younger. In an interview in the March 2008 newsletter to the Grant Study subjects, Vaillant was asked, “What have you learned from the Grant Study men?” Vaillant’s response: “That the only thing that really matters in life are your relationships to other people.”