Harvard started looking into this in 1938 when the Harvard Study of Adult Development kicked off. Over 79 years, researchers tracked 724 men -- one group was Harvard College freshmen, the other men from the poorest parts of Boston.
The most important finding of this study is that health flows from how happy people are with their relationships. If people are isolated or suffer from conflict-ridden relationships, their health and happiness deteriorate. If people have good relationships with family, friends, and the community, they live longer, they're healthier, and they're happier.
Here are three things I think you should do to benefit from the findings of this study.
1. End or repair toxic relationships.
The Harvard study found that living in conflict is bad for people's physical and emotional health. Fixing toxic relationships is the most time-sensitive problem in a person's life. Health and happiness can improve most quickly by making a change in any relationship that leaves you feeling tired of fighting at the end of each day.
You could either end the relationship altogether -- or seek counseling to try to repair the relationship. But the key thing to remember is that you will never be happy as long as you stay in toxic relationships. The pain of ending such relationships may be extreme in the short run -- but the longer-term benefit for your health and happiness will more than offset that pain.
2. Revive and strengthen relationships with family and old friends.
Don't let your relationships with family and old friends go stale. Instead, put energy into making those ties fresh by doing new things together. If you can't see these people as often as you used to, find ways to keep in regular contact.
Robert Waldinger, the director of the Harvard study and a Harvard Medical School psychiatry professor, said it doesn't matter how many friends you have -- but the quality of your close relationships is vitally important.
He said all your close relationships should be "good, warm, and close." Indeed, he found that as people age, such relationships will help them cope with challenges such as physical pain. Conversely, people in relationships that are full of conflict find that any physical pain they suffer is compounded by emotional pain.
3. Keep building new, positive relationships.
A logical corollary of the first two suggestions is that you should keep cultivating new relationships as you age. After all, people you've known since you were younger may move away or get too consumed by their daily challenges to make time for continuing the old friendships.
If you can find a way to build new, positive relationships, you will keep your mind active and enjoy the benefits of both the joy and support from the new relationships combined with the closeness and ease of the relationships you've built with family and friends.
I've found that teaching college is a great way to do this. Relationships built with professional colleagues and students are a source of satisfaction. It feels to me as though helping people starting out in their careers is a good thing to do. And helping new students and ones who have graduated is a life-affirming activity.
Do these three things and happiness, health, and long life could be yours.