Happy people live longer, a relationship that's been documented in a variety of research studies.
But a new paper published in the medical journal Lancet comes to the sad conclusion that happiness isn't responsible for this observed longevity. Instead, the things that make people happy, particularly their good health, are the same things that shield them from premature death.
"Happiness and related measures of well-being do not appear to have any direct effect on mortality," the study authors wrote.
To get to the bottom of the relationship between happiness and a long life, researchers led by Dr. Bette Liu, an epidemiologist at the University of New South Wales in Sydney, examined data on 719,671 people who participated in the Million Women Study. All of the women joined the study from 1996 to 2001.
Three years after signing up, researchers asked them how often they felt happy. The 39% who answered "most of the time" and the 44% who answered "usually" were classified as happy people. The other 17%, who said they were "sometimes" or "rarely/never" happy, were deemed unhappy.
At the same time, the women were also asked to rate their health status as "excellent," "good," "fair" or "poor." Then researchers kept track of them for nearly 10 years, on average. During that time, 31,531 (or 4%) of them died.
In their first pass at the numbers that adjusted for age, the researchers found that women who said they were unhappy were 29% more likely to have died compared with their counterparts who were happy. But the women who were unhappy were also more likely to be in poor health. Once the researchers took that into account, the association between happiness and mortality disappeared. That held up after the team added in variables such as socioeconomic status, exercise and sleeping habits; whether they lived with a partner; and whether they were religious.
The 20% of women who rated their health as fair or poor at the start of the study were 67% more likely to die during the study period than the 80% of women who rated their health as excellent or good. But in each group, the women who said they were happy had the same odds of dying as the women who said they were unhappy.
When the researchers focused just on women who died of heart disease or cancer, the results were the same: Those who were happy at the start of the study were just as likely to die as their unhappy counterparts.
Finally, the researchers took a slight detour from happiness to see whether women who felt they were "in control, relaxed, or not stressed" had any protection against an early death. Among the women who said their health was excellent or good, these stress-related measures had no bearing on mortality risk, the researchers found.
"Our large prospective study shows no robust evidence that happiness itself reduces cardiac, cancer, or overall mortality," they concluded.
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