Happy people are healthier and live longer, or so the conventional wisdom goes.
But happiness isn't the reason some people have longer lives, according to a study published on Wednesday in The Lancet.
Researchers analyzed data on nearly 720,000 women ages 50 to 69 who joined the so-called Million Women Study between 1996 and 2001. Three years after they joined, researchers asked the participants how often they were happy. The more than 80% of women who answered "usually" or "most of the time" were classified as happy, while the remaining women were classified as unhappy.
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The researchers also asked the women to rate their health status on a scale from "excellent" to "poor," and tracked the women for an average of almost 10 years. Over that time period, 4% of the study participants died.
After adjusting for age, the researchers found that the "unhappy" women were 29% more likely to have died compared with the "happy women."
But when they adjusted for self-reported health, that association disappeared. There was also no association between happiness and mortality when the researchers also adjusted for variables such as exercise, sleeping habits, socioeconomic status, if they were religious, and if they lived with a partner.
The researchers found the same lack of correlation when they focused just on women who had died of cancer or heart disease.
The study authors said earlier research that showed a correlation mixed up cause and effect, and that it's being unhealthy that causes unhappiness, and not the reverse.
"You could say it's good news for the grumpy," says study co-author Sir Richard Peto, a professor of medical statistics and epidemiology at the University of Oxford.
It's unclear whether the findings also hold true for men, Denise Grady writes for the New York Times.
In a commentary accompanying the study, researchers from University Hospital of Toulouse in France speculated that the results might be different because "men and women probably define happiness differently."
The editorial praised the study for its statistical methods and said it had "the largest population so far in happiness studies." However, the authors said more research is needed (Grady, New York Times, 12/9; Cheng, AP/U.S. News & World Report, 12/10; Kaplan, "Science Now," Los Angeles Times, 12/9; Beck, The Atlantic, 12/9).
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