The Harvard Study of Adult Development began in 1938, when researchers started tracking 268 Crimson sophomores. Among the early participants: future president John F. Kennedy and Washington Post editor Ben Bradlee.

It’s one of the longest longitudinal studies in the world. And it has found that having close relationships is the best predictor of longevity—and helps delay mental and physical decline.

That’s reassuring for retirees who are surrounded by loving family and friends. But what if you’re isolated—or estranged—from loved ones?

“People do better when they have close relationships,” said Mark Sichel, a licensed clinical social worker in Austin. “And if you can’t have close relationships with family, you can create a second family with close friends.”

For retirees who have drifted apart from family members, reconciliation has its benefits. Aside from boosting your odds of living longer, there’s joy in re-establishing a severed relationship.

Author of “Healing From Family Rifts,” Sichel decided to reconcile with his estranged father in 2006. His father was dying from leukemia, and Sichel says he “just showed up in the hospital” to reconnect.

“You have to make the first move,” he said. “That’s the only way to unfreeze a relationship that’s been frozen.”

It’s normal to fear rejection or conflict if you attempt to reconcile. But for Sichel, the gambit paid off instantly.

“My father was delighted to see me,” he recalled. “I dropped my grievances and he dropped his grievances. It was immediate.”

Sichel’s motive in seeing his father wasn’t to raise his longevity. He simply wanted to end the estrangement.

“It won’t work if you’re doing it for extended life,” he warned. “It’ll work if you think [fondly] of the past and you’re very interested in the other person.”

Fixing a broken relationship requires hard work. If you see it as one more step to add years to your life (like limiting your caloric intake or taking a daily walk in the woods), think again.

“The idea of a longer life is so abstract,” said Joshua Coleman, Ph.D., author of “Rules of Estrangement.” “You may want more concrete reasons to repair a relationship. The abstract notion of longevity may not be sufficiently stimulating and motivating to get you to do the work” that reconciliation entails.

What’s more, some relationships cannot be repaired. Others “may have broken up with us,” Coleman says, and shut down our attempt to re-enter their life.

If you’re going to initiate contact, brace for impact. Don’t assume it will go smoothly like Sichel’s hospital visit with his father.

“If you take the high road, the other person may not be able or capable of responding at the same level,” Coleman said. “You may need to take more responsibility than you think is right or fair.”

What should you talk about? Do you begin with an apology and hope to hear one in return?

That’s a risky strategy. Rather than focus on who was right and who was wrong, skip to a safer topic. Look ahead and express interest in strengthening ties.

“It’s better to discuss new shared experiences,” Sichel said. “You need to make a decision that it’s useless to stay attached to grievances and cling to resentments. If you obsess and ruminate about what they did to you, it’s making you sick. It’s not making them sick.”

For many retirees, the problem isn’t fixing a breach in a once-treasured relationship. The real challenge is assessing whether you have the kind of high-quality relationships that breed longevity.

Lucy Blake, Ph.D., a senior lecturer in psychology at the University of the West of England, cites two characteristics of these solid relationships: they are relatively conflict-free and there’s a longstanding affection that both parties share.

“High-quality relationships have fairly low or average levels of conflict,” said Blake, author of “Home Truths.” “And if there is conflict, it’s resolved well. The second thing is there are warm feelings for the other person.”

Because extreme loneliness can contribute to mortality, it’s never too late to forge bonds with those around us. Even if you no longer enjoy close relationships with family or friends, embracing an active social life can lay the groundwork for quality relationships to bloom.

There’s no guarantee that happy relationships will prolong your life. But it’s worth trying to cultivate as many of them as you can, while you can.