Always look on the bright side of life ...

You won't only feel better, you might get to live longer too, if the latest research is to be believed
A Pakistani young couple walk on a beach on 2007's Valentine's Day in Karachi
Is life a beach or a bitch? Photograph: Asif Hassan/AFP/Getty Images

Is it possible that having a sunny outlook on life can be good for your health? Plenty of self-help guides claim that positive thinking can improve wellbeing, but is there any scientific evidence for this?

A huge new study in the US found that optimists were less likely than pessimists to develop coronary heart disease (CHD) and less likely to die of any cause over the course of the eight-year trial. Hilary Tindle and colleagues looked at 97,253 postmenopausal women, all of whom were free of cancer and cardiovascular disease when they took personality tests at the start of the study.

When the researchers compared the most optimistic 25% of their subjects with the most pessimistic 25%, they found that out of every 10,000 optimists, 43 developed CHD and overall 46 died, while for every 10,000 pessimists there were 60 cases of CHD and 63 deaths overall. Women who scored highly for "cynical hostility" were also more likely to develop CHD or die. The study was published this week in Circulation, a journal of the American Heart Association.

This isn't the first study to find a link between optimism and good health.

Psychologists distinguish two different kinds of optimism. "Dispositional optimism" is the general belief that good things will happen. On the other hand a person is said to have an optimistic "explanatory style" if they blame bad things on temporary, external factors; and a pessimistic explanatory style if they believe bad things happen because of their own fault or unchangeable, global factors.

One study, reported in 1988, looked at 99 Harvard graduates from the classes of 1942-1944, all of whom filled in questionnaires that determined their explanatory style at the age of 25. When doctors examined their physical health over the next 35 years, they found that those who were pessimistic when they left university were more likely to experience poor health between the ages of 45 and 60, taking into account their physical and mental health at 25.

A study in 2001 of 1,306 men found that those whose explanatory style was most optimistic were less than half as likely to develop coronary artery disease compared with those who were most pessimistic.

A Dutch study of 941 subjects aged 65-80, published in 2004, found that those of a pessimistic disposition were 55% more likely to die during the nine-year follow-up period, independent of other factors such as education, smoking and alcohol consumption. The effect was particularly strong in men.

A study in the US in 2006 looked at 6,958 students who had taken a psychological test when they enrolled at the University of North Carolina in the 1960s. Among the most pessimistic third of the subjects, the death rate over the next 40 years was 42 per cent higher than among the most optimistic third.

Dispositional optimism has also been linked with improved recovery rates after surgery and improved cancer survival rates.

We shouldn't leap to the conclusion that being optimistic makes people healthier. It could be that good health is what is making people optimistic in the first place, and not the other way around. Healthier people are certainly likely to be more optimistic, but studies have generally accounted for this and still found a positive result, so it doesn't seem to be the whole story. When subjects have been followed for several decades after the original questionnaire, we can be even more confident that the bad health wasn't there to begin with.

Another possibility is that optimists lead healthier lifestyles, as Dr Tindle points out. "In our study," she told me, "optimists tended to be slightly younger, more educated and wealthier, more physically active and closer to healthy body weight." But other studies have still found optimism to have a beneficial effect even after adjusting for known cardiovascular risk factors.

Although Dr Tindle stressed that her study could not identify the physiological link between optimism and health, she did suggest that optimists might have better ways of coping with stress. "This could mean not as much of a rise in blood pressure, stress hormones, or heart rate," she said.

Perhaps our genes could also be playing a role. It might be that the same genes that confer an optimistic disposition also predispose to good health.

To demonstrate a causal relationship between optimism and health, you'd need to do a randomised trial in which a group of pessimists was somehow turned into optimists, and then wait and see whether they fared any better than a control group.

As things stand, it's still unclear whether adopting a more positive outlook on life can reduce your likelihood of falling ill or dying. But it certainly won't hurt – and it might put a smile on your face. Who could argue with that?