Optimists don’t always fare better than pessimists in their immunologic response to stress, a new review of studies finds.

The difference between optimists and pessimists seems to be based on the degree of stress facing the optimist and the degree to which a pessimist avoids the problem, according to an article in the current issue of the journal Brain, Behavior, and Immunity by Suzanne Segerstrom, Ph.D., of the University of Kentucky.

“There is sometimes a physiological cost to be paid for the optimistic strategy of engaging difficult stressors rather than disengaging and withdrawing,” Segerstrom writes, instancing the higher levels of the stress hormone cortisol and lower levels of cellular immunity in people with HIV.

The studies she reviewed were mixed on the overall effects of optimism on immunity, but Segerstrom concludes that when stressors are easy, optimism can have a positive effect on the immune system.

When stressors are difficult, however, some studies have shown that optimists are less likely to disengage from or avoid the problem, which may have a negative effect on their immune systems.

Put another way, when an optimist is faced with a serious health or other problem that cannot be resolved, the disappointment — and thus the negative immune response — is greater than that of the pessimist, who did not have high hopes in the first place or who might have simply avoided the issue. 

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