A review of more than 160 studies of human and animal subjects has found "clear and compelling evidence" that - all else being equal - happy people tend to live longer and experience better health than their unhappy peers.
The study, in the journal Applied Psychology: Health and Well-Being, is the most comprehensive review so far of the evidence linking happiness to health outcomes. Its lead author, University of Illinois professor emeritus of psychology Ed Diener, who also is a senior scientist for the Gallup Organization, of Princeton, N.J., analyzed long-term studies of human subjects, experimental human and animal trials, and studies that evaluate the health status of people stressed by natural events.
"We reviewed eight different types of studies," Diener said. "And the general conclusion from each type of study is that your subjective well-being - that is, feeling positive about your life, not stressed out, not depressed - contributes to both longevity and better health among healthy populations."
A study that followed nearly 5,000 university students for more than 40 years, for example, found that those who were most pessimistic as students tended to die younger than their peers. An even longer-term study that followed 180 Catholic nuns from early adulthood to old age found that those who wrote positive autobiographies in their early 20s tended to outlive those who wrote more negative accounts of their young lives.
There were a few exceptions, but most of the long-term studies the researchers reviewed found that anxiety, depression, a lack of enjoyment of daily activities and pessimism all are associated with higher rates of disease and a shorter lifespan.
Animal studies also demonstrate a strong link between stress and poor health. Experiments in which animals receive the same care but differ in their stress levels (as a result of an abundance of nest mates in their cages, for example) have found that stressed animals are more susceptible to heart disease, have weaker immune systems and tend to die younger than those living in less crowded conditions.
Laboratory experiments on humans have found that positive moods reduce stress-related hormones, increase immune function and promote the speedy recovery of the heart after exertion. In other studies, marital conflicts and high hostility in married couples were associated with slow wound healing and a poorer immune response.
"I was almost shocked and certainly surprised to see the consistency of the data," Diener said. "All of these different kinds of studies point to the same conclusion: that health and then longevity in turn are influenced by our mood states."
While happiness might not by itself prevent or cure disease, the evidence that positive emotions and enjoyment of life contribute to better health and a longer lifespan is stronger than the data linking obesity to reduced longevity, Diener said.
"Happiness is no magic bullet," he said. "But the evidence is clear and compelling that it changes your odds of getting disease or dying young."
"Although there are a handful of studies that find opposite effects," Diener said, "the overwhelming majority of studies support the conclusion that happiness is associated with health and longevity. Current health recommendations focus on four things: avoid obesity, eat right, don't smoke, and exercise. It may be time to add 'be happy and avoid chronic anger and depression' to the list."
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