t’s an in-vogue area of research right now: studies showing that people who are happy, or less lonely, or more optimistic, live longer lives. There are reasons this might be so — happy people might exercise more, for instance, or happiness might cause healthful changes in certain hormone levels. The idea has spawned various interventions to increase people’s happiness as a way to benefit their health.

However a new study indicates that the causation might work in the opposite direction — health status affects how happy people are. In other words, people who are sick are unhappy.

That’s the finding of a survey of 1.3 million women in the United Kingdom which asked about their happiness and then followed their health over an average of nine years afterward. They found that women who were happy “most of the time” were significantly less likely to die in the subsequent years than women who reported being sometimes or never happy.


But that connection went away when they factored in participants’ self-reported health. Healthy people at the outset of the study were less likely to die and more likely to describe themselves as happy. Thus, it wasn’t the happiness that was changing their health, but the other way around, researchers report in the paper published Wednesday in The Lancet.

“People who have ill health are unhappy, and the cause is illness,” said Sir Richard Peto, professor of medical statistics and epidemiology at the University of Oxford and author of the study. “We’ve got the numbers that show that unhappiness has no material relevance to death at all.”

The only exception appeared to be smoking. Unhappy people were more likely to smoke, and that increased their risk of dying. But this effect was small by comparison, leading researchers to conclude that happiness has little impact overall on how long a person will live.

In an accompanying commentary, a pair of scientists in France suggested that the results might not be the same in men, since “men and women probably define happiness differently.” Men’s health might, therefore, benefit more from happiness-boosting interventions.

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