In an observational study, a nationally representative group of 6,044 adults over age 50 rated their optimism levels on a 16-point scale. Each point increase in optimism corresponded to a 9 percent decrease in acute stroke risk over a two-year follow-up period.

"Our work suggests that people who expect the best things in life actively take steps to promote health," said Eric Kim, study lead author and a clinical psychology doctoral student at the University of Michigan.

Optimism is the expectation that more good things, rather than bad, will happen.

Previous research has shown that an optimistic attitude is associated with better heart health outcomes and enhanced immune-system functioning, among other positive effects.

The study is the first to discover a correlation between optimism and stroke. Previous research has shown that low pessimism and temporary positive emotions are linked to lower stroke risk. Researchers analyzed self-reported stroke and psychological data from the ongoing Health and Retirement Study, collected between 2006 and 2008. Participants were stroke-free at the beginning of the study.

Researchers measured optimism levels with the modified Life Orientation Test-Revised, a widely used assessment tool in which participants rank their responses on a numeric scale.

The team used logistic regression analysis to establish the association between optimism and stroke and adjusted for factors that might affect stroke risk, including chronic illness, self-reported health and sociodemographic, behavioral, biological and psychological conditions.

"Optimism seems to have a swift impact on stroke," said Kim, noting that researchers followed participants for only two years. The protective effect of optimism may primarily be due to behavioral choices that people make, such as taking vitamins, eating a healthy diet and exercising, researchers said. However, some evidence suggests positive thinking might have a strictly biological impact as well.

Stroke is the No. 3 killer in the United States, behind heart disease and cancer, and a leading cause of disability.

Co-authors of the study are Nansook Park, Ph.D., and Christopher Peterson, Ph.D. Author disclosures are on the manuscript.

The Robert Wood Johnson Foundation's Pioneer Portfolio funded a part of the study through the Positive Psychology Center of the University of Pennsylvania.