Even though poor health is a known cause of unhappiness, and bad lifestyle choices often follow bad moods, misery alone probably won't kill you, a U.K. study suggests.
"We found that after accounting for poor health and other lifestyle choices, being happier doesn't make you live longer, and being stressed doesn't increase your risk of death," lead study author Bette Liu of the University of New South Wales said by email.
To explore the connection between unhappiness and the likelihood of dying, Liu and her colleagues looked at data on more than 700,000 middle-aged women collected over more than a decade. At the start, when the women were around 59 years old, 17 percent reported being unhappy, and this was more likely in women who were in poor health.
During the next ten years, about 31,500 women died, representing about 4 percent of the study population.
After researchers adjusted for a host of factors independently linked to mortality - like hypertension, diabetes, smoking, drinking, asthma, arthritis, depression and anxiety - mere unhappiness wasn't associated with increased mortality from all causes, or specifically from cancer or heart disease.
The data was collected from 1996 to 2001. When they joined the study, and again every 3 to 5 years, women completed questionnaires asking about social and demographic factors, lifestyle choices and health.
At the start of the study, 39 percent said they were happy most of the time, and another 43 percent described themselves as usually happy. Researchers counted as "unhappy" the 16 percent of women who were happy only sometimes and the 1 percent who said this was a rare occurrence.
Over time, few women changed their assessment of their own happiness levels, the researchers report in The Lancet.
Generally, the happy women in the study were older, less likely to have advanced degrees and more likely to be nonsmokers as well as regular exercisers with steady romantic relationships who routinely participated in religious or other group activities. These happy women were also more likely to get eight hours of sleep each night.
In contrast, the unhappy women were more likely to report only fair or poor general health and to be in treatment for depression or anxiety, the study found.
Women were 20 percent more likely to die during the study if they reported being in fair or poor health.
There is no perfect way to measure happiness, the authors concede. Unhappiness might, however, lead people to do things known to hasten death like drink too much or exercise too little, they speculate.
"Previous reports of reduced mortality associated with happiness could be due to the increased mortality of people who are unhappy because of their poor health," the study team points out.
It's also important to note that death isn't the only outcome that matters when assessing the benefits of happiness, noted Philipe Barreto a researcher at the University Hospital of Toulouse in France who wrote an accompanying editorial.
Even if happiness won't impact life expectancy, it will probably be associated with quality of life, Barreto said by email.
"In other words, even if happiness does not add years to life, it probably adds life to years," Barreto said.