In the quest for better health, many people turn to doctors, self-help books or herbal supplements. But they overlook a powerful weapon that could help them fight illness and depression, speed recovery, slow aging and prolong life: their friends.

Researchers are only now starting to pay attention to the importance of friendship and social networks in overall health. A 10-year Australian study found that older people with a large circle of friends were 22 percent less likely to die during the study period than those with fewer friends. A large 2007 study showed an increase of nearly 60 percent in the risk for obesity among people whose friends gained weight. And last year, Harvard researchers reported that strong social ties could promote brain health as we age.

“In general, the role of friendship in our lives isn’t well appreciated, ”said Rebecca G. Adams, a professor of sociology at the University of North Carolina, Greensboro. “There are a lot of things on families and marriage, but very little on friendship. It baffles me. Friendship has a bigger impact on our psychological well-being than family relationships. ”