"Every friend makes you healthier; every friend makes you happier," Fowler says. "We're not talking about your 500th friend on Facebook. We're talking about your dearest and closest friends, and these people are hard to find."
Antonucci has a different view. Human relationships have negative as well as positive consequences, and a friendship that has turned toxic is not worth keeping. "Nobody can drive you quite so crazy as someone who is near and important to you," she says. "One of the things people have to do is to learn when to give up on a relationship and how to do it."
The good news about friendships is that they get better with age, says Karen Fingerman, professor of human development and family science at the University of Texas. "It almost doesn't matter what relationship you're talking about. They get better when you get older." Older people are generally more happy and forgiving and less judgmental than younger people. They also are less driven by emotions and hormones and do a better job of controlling their behaviors.
The number and diversity of friendships tend to naturally decline in later years, and can lead to isolation and adverse effects on health and happiness. Psychologist Laura Carstensen, who directs the Stanford Center on Longevity, says people should consider paying attention to the diversity and ages of people in their circle of friends. This can minimize the serious impact of having all your friends die off, she says.
Developing and maintaining friendships requires continuous attention. "Give-and-take is important," Blieszner says. Other elements of solid friendships, she notes, include paying attention to what's going on in a friend's life, seeking out and participating in shared interests and activities, and being able to confide deeply to a friend.
"People should learn to value relationships," Antonucci concludes. "They will make them happier. And with longer life expectancies, they really have to think about the kind of life they want to lead ... I think we underestimate how important it is in our lives to have relationships."