Having an optimistic outlook on life may not always guarantee a better reaction to stress, as measured by a person’s immune status, according to a University of Kentucky psychologist. On the other hand, it doesn’t seem to do any harm to have a sunny disposition.

Dr. Suzanne C. Segerstrom reviewed several studies on the topic and found that some researchers reported that optimism was associated with better immunity, while others didn’t.

“Optimism has varied relationships to the immune system, depending on the context and the type of optimism,” said Segerstrom. Yet, she added, none of the available research suggests that optimism is associated with worse health outcomes.

Various researchers have found that people with the most positive outlook about their futures tend to have better moods, fewer psychiatric symptoms and better adjustment to pregnancy, heart surgery and other situations. Research also suggests that optimism is linked to better physical health.

Still, there have been conflicting reports of its effect. Optimism has been linked to a lower risk of death among patients with head and neck cancer, for example, but not among patients with lung cancer. Similarly mixed results have been found in studies of patients with HIV.

The varying effects of optimism may be partly explained by the “disappointment hypothesis,” the report indicates. This suggests that when a stressor, such as a serious health problem or other circumstance, is prolonged, it violates “optimists’ positive expectations that they could terminate or control the stressors.” This leads to distress, which consequently lowers immunity, Segerstrom writes in the current issue of Brain, Behavior, and Immunity.

In one report, for example, optimistic women were unaffected by increasing stress levels during a one-week study period, whereas their pessimistic peers experienced a decline in their percentages of T cells - i.e. lower immunity. When the stress lasted longer than a week, however, immunity declined among the optimistic women so that the two groups ended up at about the same level.

Another theory, the “engagement hypothesis,” suggests that optimistic people remain engaged in difficult situations whereas pessimistic individuals disengage themselves. This can be good or bad, depending on whether the situation can be resolved quickly or not. A rapid solution would associate optimism with positive effect on immunity, whereas prolonged involvement in a difficult stressful situation, leading to depressed immunity, would show optimism is not protective.

Thus, “how optimism affects the immune system critically depends on the circumstances being examined,” Segerstrom concludes. “However,” she writes, “it is clear that to the question of whether optimism is good or bad for immunity: the answer is ‘yes.’”

Despite these inconclusive findings, Segerstrom notes that since optimism has been found to be sometimes associated with better outcomes, “there doesn’t seem to be anything to lose by being optimistic in terms of long-term health outcomes.”

SOURCE: Brain, Behavior, and Immunity, May 2005.