In her widely celebrated 1978 book Illness as Metaphor Susan Sontag wrote that when medical experts attribute psychological causality to biological disease, they “assign to the luckless ill the ultimate responsibility both for falling ill and for getting well.” The latest salvo in the ongoing debate over the extent to which psychological factors can explain physiological outcomes comes from a study published today, which finds optimistic women are less likely to die of a variety of illnesses—from cancer to heart failure to infectious disease.

Researchers from Harvard University's T. H. Chan School of Public Health turned to a 40-year survey-based study begun in 1976 of American female nurses, most of whom were white, called the “Nurses’ Health Study.” They extracted data on the women's personalities from the 2004 and 2008 surveys and compared it with mortality rates for the same women between 2006 and 2012. Altogether, they collected information from more than 70,000 individuals. To assess optimism, the study asked participants to rate on a five-point scale the extent to which they agreed with six statements such as, “in uncertain times, I usually expect the best.”

“When comparing the top 25 percent most optimistic [women] to the bottom 25 percent, they had about a 30 percent reduced risk of mortality,” says study leader Eric Kim of Harvard. Those relationships remained, albeit less robustly, even after the researchers adjusted the predictions to account for sociodemographic factors and health-related behaviors. Kim is quick to point out that this does not necessarily mean optimism leads to healthier lifestyles, only that there is a statistical association. Still, he and his colleagues argue that because personality traits are somewhat malleable, optimism-based interventions could be a fairly simple, low-cost way to improve public health.

Such interventions might include “structured classroom-style instruction” and “brief paper-and-pencil exercises in which people are asked to write about a best possible version of themselves,” the researchers report in the American Journal of Epidemiology.

The idea that with a few hours of effort we might be able to stave off a range of existential threats—including cancer, heart disease, stroke, respiratory disease and infection—may sound enticing. Intrinsic to the argument seems to be a promise: If you're more optimistic, you will keep death from knocking at your door, at least for a little while. But not all experts agree.

The problem with suggesting positive thinking can ward off death, some experts say, is that it makes chronic disease patients feel guilt or shame—that they are somehow responsible for their illness. Furthermore, if optimism is associated with better health, it may have more to do with the fact people who are not optimistic may in fact suffer from clinical depression, which is widely linked to poorer health.

Kim argues, however, that optimism is “something above and beyond the absence of depression,” and the results hold up even after statistically controlling for the potentially confounding role of the disorder. Optimism and the lack of depression may at first seem like two sides of the same coin, but depression is a wide-ranging syndrome that affects physiology as well as psychology. Just as you cannot simply think yourself out of a stroke, you also cannot think yourself out of major depressive disorder.

Kim agrees there is danger in overreliance on psychological rhetoric when it comes to understanding the origins of disease or illness. “We definitely don't want to victim-blame anyone,” he says, but “we can, as a society, construct environments where people have an equal opportunity for becoming more optimistic.” He thinks of optimism interventions as “one of the tools in a broad toolkit” that ought to be available to people to enhance their health and well-being.

The findings align with previous studies, which have found links between optimism and heart health. For example, a 2015 review of 30 studies found positive outlooks were associated with both reduced mortality and reduced rate of rehospitalization in patients who had cardiovascular diseases. On the other hand, a 2013 study found those who are overoptimistic have a greater risk of death or disability, and that a little pessimism could motivate people to behave more carefully. The truth may lie somewhere in between: which outlook is most helpful may depend on individual circumstances.

Ultimately, dispositional optimism is embedded within our personalities, which are, by definition, supposed to be stable across time and among different circumstances. And although personalities may change slowly over time, the notion that a paper-and-pencil intervention can result in changes to the fundamental organization of our core psychological traits is debatable, even if they may indeed reliably result in short-term attitudinal shifts.

Emanuel Maidenberg, a professor of clinical psychiatry at the University of California, Los Angeles, agrees, comparing the premise of optimism interventions to better-established tools for promoting health and wellness such as physical exercise and eating well.

These are lifestyle changes, he says, and the purported benefits of such interventions would certainly not be achievable after just a few hours in a classroom. “These are tools that have to be considered as ongoing maintenance for a particular state of being.” In other words, there are no shortcuts to a longer life.