Friendship is key to staying well, says Alice Domar Ph.D., founder of the Domar Center for Mind/Body Health. “People who have inadequate social support are as likely to die early as people who smoke or have high cholesterol.”

She recommends keeping two kinds of relationships going. “You need your foxhole friends, who will be there for you at 2 am and your party friends, you make you laugh,” she says. What you don’t need? Unhealthy relationships. These can prove as bad for you as total isolation. “If there are people in your life who suck you dry, break up with them,” says Domar. “There is nothing wrong with that.”