Happiness not linked to mortality, study says

There is no evidence that happiness in and of itself has any effect on reducing mortality, despite widespread belief that unhappiness and stress can cause poor health, according to a new study. 

It's actually the other way around, the authors say. 

"Illness makes you unhappy, but unhappiness itself doesn't make you ill," lead author Dr. Bette Liu of the University of New South Wales, Australia, said in a news release issued by The Lancet medical journal, where the study was published Wednesday.  

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The findings are based on data from The Million Women Study in the U.K., which recruited 1.3 million women between 1996 and 2001 through national breast screening programs in England and Scotland. The happiness study analyzed health data for more than 700,000 of those women, who were mostly between the ages of 55 and 63.

Three years after joining the study, the participants were sent a questionnaire asking them to rate their health, happiness, stress levels, feelings of control and whether they felt relaxed. About one out of six said they were generally unhappy. 

"As in other studies, unhappiness was associated with deprivation, smoking, lack of exercise, and not living with a partner," the news release said. "The strongest associations, however, were that the women who were already in poor health tended to say that they were unhappy, stressed, not in control, and not relaxed."

'Confusing cause and effect'

The researchers used the results of the questionnaire as a baseline for investigating the link between happiness and mortality for 30,000 women who died during 10 years of follow-up. The study adjusted for health factors (including hypertension, diabetes, asthma, arthritis, depression and anxiety) and lifestyle factors (including smoking) that were already present at the baseline measurement phase.

After taking those factors into account, the researchers found the overall death rate was the same for people who were generally happy as those who were generally unhappy. 

Many still believe that stress or unhappiness can directly cause disease, but they are simply confusing cause and effect," said co-author Richard Peto, an epidemiology professor at the University of Oxford. "Of course people who are ill tend to be unhappier than those who are well, but the U.K. Million Women Study shows that happiness and unhappiness do not themselves have any direct effect on death rates."  

The study also suggested that people might associate unhappiness with higher mortality because people who aren't happy might be more likely to smoke, which is a risk factor for cancer deaths.  

The researchers claimed previous reports suggesting happiness was associated with reduced mortality did not adequately account for how strongly poor health decreases happiness.  

In a Lancet article commenting on the study, experts from the Institute of Aging at the University Hospital of Toulouse, France, said the research "provides extremely valuable and robust information about happiness, health, and mortality," but emphasized the need for more studies looking at both men and women, different age groups, and different cultures.