A cheerful disposition can help you get through the tough patches that cloud every life, but do people who see the glass half-full also enjoy better health than gloomy types who see it half-empty?

According to a series of studies, the answer is yes. Research shows an optimistic outlook early in life can predict better health and a ­lower rate of death during follow-up periods of 15 to 40 years.

Optmism and Blood Pressure

A sunny outlook could reduce the develop­ment of hypertension, which is a major risk of cardiovascular disease. Scientists evaluated the cardiovascular risk factors (smoking, obe­sity, physical inactivity, alcohol abuse, and family history of hypertension) for 616 middle­-aged men with normal initial blood pressures and questioned them about their expectations for the future. Over a four-year period, highly pessimistic men were three times more likely to develop hypertension than cheerier souls.

Optimism and Heart Disease

If optimism can reduce the risk of hyperten­sion, can it also protect against developing coronary artery disease? To find out, scientists from Harvard and Boston University evaluated 1,306 men with an average age of 61. Each volunteer was evaluated evaluated for an optimistic or pessimistic explanatory style, blood pressure, cholesterol, obesity, smoking, alcohol use, and family history of heart disease. None of the men had been diagnosed with coronary artery disease before the study. Over the next 10 years, the most pessimistic men were more than twice as likely as the most optimis­tic men to develop heart disease.

Optimism and Survival

According to two studies from the U.S. and two from the Netherlands, optimism also boosts longevity. The first American study evaluated 839 people in the early 1960s, performing a psychological test for optimism-pessimism as well as a complete medical evaluation. When the participants were rechecked 30 years later, optimism was linked to longevity; for every 10-point increase in pessimism on the optimism-pessimism test, the mortality rate rose 19 percent. A newer study looked at 6,959 students who took a comprehen­sive personality test. During the next 40 years, 476 people died from a variety of causes, with the most pessimistic individuals having a 42 percent higher rate of death than the most optimistic.

Possible Mechanisms

Taken together, these studies argue persuasively that optimism is good for health – but why?

Perhaps optimism is actually the result of good health instead of the other way around. To counter this argument, research­es [sic] adjusted their studies for pre-existing medical conditions and found that these medical conditions did not tarnish the ben­efits of a bright outlook on life. Moreover, by tracking people for 15, 30, and 40 years, scientists can minimize the potential bias of pre-existing conditions.

Another explanation is behavioral. It is pos­sible that optimists lead healthier lifestyles, build stronger social support networks, and get better medical care. Studies report that optimists are more likely to exercise, less likely to smoke, more likely to live with a spouse, and more likely to follow medical advice than pessimists. Although optimism is not generally associated with a better diet or a leaner physique, and even when results are adjusted for cardiovascular risk factors, a beneficial effect of optimism persists. In addition to behavioral advantages, opti­mism may have biological benefits that im­prove health. A 2008 study of 2,873 healthy men and women found that a positive outlook on life was linked to lower levels of the stress hormone cortisol, even after taking age, em­ployment, income, ethnicity, obesity, smok­ing, and depression into account. In women, but not men, optimism was also associated with lower levels of two markers of inflammation (C-reactive protein and interleukin-6), which predict the risk of heart attack and stroke. Other possible benefits include reduced levels of adrenaline, improved immune function, and less active clotting systems.

Finally, heredity may explain some of the link. It is possible that genes predispose some people to optimism, and that the same genes exert a direct effect on health and longevity.

Blue Skies

More research is needed to clarify the link be­tween optimism and good health since it is likely that multiple mechanisms are involved. Personality is complex, and doctors don't know if optimism is hard-wired into an individual or if a sunny disposition can be nurtured in some way. It's doubtful that McLandburgh Wilson was pondering such weighty questions when he explained optimism in 1915:

“Twixt the optimist and pessimist / The difference is droll / The optimist sees the doughnut / But the pessimist sees the hole.”

Today’s doctors don't think much of dough­nuts, but they are accumulating evidence that optimism is good for health. As you await the results of new research, do your best to seek silver linings, if not doughnuts.

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