Sixty years after the launch of the Grant Study of human happiness, University of Pennsylvania psychologist Martin Seligman developed a new field known as positive psychology that attempts to identify and reinforce virtuous traits that can help people lead healthy, happy lives. Researchers have long studied how negative emotions, such as hostility and depression, might contribute to diseases and untimely deaths. Now there is an interest in researching claims that positive affect, or PA—feelings of happiness, contentment, vigor and calm—may help ward off illnesses and enhance longevity.

At least 30 studies have shown that older people who rate high on PA scales tend to live longer than those who have fewer of those feelings, says Sarah Pressman, assistant professor of psychology and social behavior at University of California, Irvine.  In one study, Pressman searched the autobiographies of 88 well-known psychologists and found that those who described their lives with more positive emotion lived up to six years longer than the psychologists who tended to be more dour.

PA also appears to be important in heading off diabetes, cardiovascular disease and stroke, and to contribute to quicker recovery from heart attacks, surgeries and hip fractures. One six-year study of seniors found that those who were happier had one-third fewer strokes than those who were less content. Pressman’s colleague, Sheldon Cohen, exposed 334 volunteers to a cold virus and found that those with higher PA had much greater resistance to getting sick.

Once illness occurs, those with PA seem to have better outcomes, provided the disease isn’t at an advanced stage. “Positive emotion won’t rebuild a kidney if you have end-stage kidney disease or get rid of millions of cancer cells replicating in your body,” says Pressman. “But there is excellent work showing that men with early-stage HIV and women with early-stage breast cancer live longer if they are happier around the time they are diagnosed.” Another study of people with sickle cell disease found that those with positive moods had fewer emergency and hospital visits, less pain and lower use of medications compared with those who were less happy.

“A main benefit of positive emotion is to undo the stress response, which plays a major role in how well our immune system fights diseases,” says Pressman. People with high PA also tend to have lower levels of stress hormones such as cortisol, and healthier hearts. Too much PA, however, can cause the opposite effect. “Very high energy emotion—vigor and excitement—can lead to potentially harmful amounts of arousal, causing rapid heart rates and increases in blood pressure,” says Pressman.

Now researchers are examining whether specific interventions can increase someone’s PA and whether changes in affect will last long enough to influence health and mortality. Pressman believes the real benefit of positive psychology will be in helping people live well with chronic diseases. “You feel better when you’re happy and you don’t notice pain and other negative symptoms as much,” she says. “If people can prevent debilitating negative emotions, their quality of life may improve and just maybe they can alter the course of their diseases.”