Having an optimistic outlook on life could help you live longer, according to a new study.
Researchers at Harvard University found that among a group of 70,000 female nurses, the 25% who were most optimistic had a 31% reduced risk of mortality while they were being tracked compared with the 25% who were least optimistic.
In the case of this study, the authors define optimism as the belief that good things will happen in the future.
"Optimists don't always present as cheerful, but they have the general expectation on the inside that things will be better," said study leader Eric Kim, a research fellow at Harvard's T.H. Chan School of Public Health in Boston.
Previous studies have shown a similar correlation between optimism and a reduced risk of dying from cardiovascular disease. However, this work was one of the first to show that optimism is also associated with reduced risk of death from infection, respiratory disease and cancer, the authors said.
The new research was published this week in the American Journal of Epidemiology.
But don't go tell a bed-ridden friend to start thinking happy thoughts just yet.
"We don't want to see victim blaming," Kim said, referencing the idea that someone who has a disease could get rid of it if they just did something differently.
"There are so many variables when it comes to what makes us sick," he said. "This is just one of them."
The findings were based on data from the Nurses' Health Study, a long-term observational study of female nurses that began in 1976.
In 2004, study participants received a survey that included a six-question measure of optimism. Respondents were asked the degree to which they agreed with statements including, "In uncertain times, I usually expect the best," and, "If something can go wrong for me, it will."
To ensure participants' answers did not represent a recent change in optimism due to an underlying health issue, the authors did not include the responses of people who died within two years after the optimism question had been posed in their analysis.
That left them with about roughly 70,000 participant responses. Those were split into four groups based on their optimism score. The makeup of the groups did not differ much in terms of socioeconomic status, the authors noted. However, more optimistic women tended to have more education and reported more physical activity.
To determine cause of death among respondents who died between 2006 and 2012, the research team consulted state vital records and the National Death Index. They were eventually able to ascertain cause of death for 98% of deceased survey respondents.
Statistical analyses revealed significant associations between increasing level of optimism and decreasing risks of mortality.
Kim said it is unlikely that simply thinking positive thoughts about the future is behind the effect he observed. Instead, he pointed to past studies that have shown optimistic people make healthier lifestyle choices.
"People who are more optimistic generally get better sleep, exercise more, and have healthier coping habits to reduce stress," he said. "These could be some of the pathways that optimism is working through."
The good news is that optimism can be taught.
Twin studies suggest that having an optimistic point of view is inherited 25% of the time, but Kim said there is also evidence that it can be learned.
For example, gratitude journals and keeping a list of the times you have been kind to others have both been shown to make small increases in optimism.
Bigger gains will require more work, however. For example, practicing mindfulness meditation on a regular basis has been shown to improve optimism, as have various types of cognitive behavioral therapy, Kim said.
And finally, if you are a pessimist and proud of it, that's fine too.
"These optimism exercises are one of many things in a healthy lifestyle toolkit," he said. "If it's something you want to pursue, the research suggests it could be helpful."
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