Optimists recover better from medical procedures such as coronary bypass surgery, have healthier immune systems and live longer, both in general and when suffering from conditions such as cancer, heart disease and kidney failure according to the Annals of Behavioral Medicine.

Researchers found that of nearly 7,000 adults followed since their college days in the 1960s, those who were optimistic in their youth had a lower risk of dying over the next 40 years than their more pessimistic peers.

On average, the most pessimistic study participants were 42 percent more likely to die of any cause than the most positive participants, according to findings published in the Mayo Clinic Proceedings medical journal.

The results echo those of a number of past studies on personality factors and health, including research that has linked optimism to longer life. One study of elderly adults found that those with a positive view of the future were less likely than pessimists to die over the next decade — regardless of their health at the start of the study.

It is well accepted that negative thoughts and anxiety can make us ill. Stress – the belief that we are at risk – triggers physiological pathways such as the “fight-or-flight” response, mediated by the sympathetic nervous system. These have evolved to protect us from danger, but if switched on long-term they increase the risk of conditions such as diabetes and dementia.

What researchers are now realising is that positive beliefs don’t just work by quelling stress. They have a positive effect too – feeling safe and secure, or believing things will turn out fine, seems to help the body maintain and repair itself. A recent analysis of various studies concluded that the health benefits of such positive thinking happen independently of the harm caused by negative states such as pessimism or stress, and are roughly comparable in magnitude (Psychosomatic Medicine, vol 70, p 741).

Researchers at the National Institute on Aging found that well-being is strongly influenced by enduring characteristics of the individual such as optimism. In a 10-year study, they found that, regardless of whether their marital status, job, or residence had changed, people with a happy disposition in 1973 were still happy in 1983. There’s good news in these findings: Given the right disposition, in the face of difficulty, people can still find renewed happiness.

Optimism seems to reduce stress-induced inflammation and levels of stress hormones such as cortisol. It may also reduce susceptibility to disease by dampening sympathetic nervous system activity and stimulating the parasympathetic nervous system. The latter governs the so-called “rest and digest” response – the opposite of fight-or-flight.

Just as helpful as taking a rosy view of the future is having a rosy view of yourself. High “self-enhancers” – people who see themselves in a more positive light than others see them – have lower cardiovascular responses to stress and recover faster, as well as lower baseline cortisol levels (Journal of Personality and Social Psychology, vol 85, p 605).

Some people are just born optimists. But whatever your natural disposition, you can train yourself to think more positively, and it seems that the more stressed or pessimistic you are to begin with, the better it will work.

David Creswell from Carnegie Mellon University in Pittsburgh, Pennsylvania, and his colleagues asked students facing exams to write short essays on times when they had displayed qualities that were important to them, such as creativity or independence. The aim was to boost their sense of self-worth. Compared with a control group, students who “self-affirmed” in this way had lower levels of adrenaline and other fight-or-flight hormones in their urine on exam day (Health Psychology, vol 28, p 554). The effect was greatest in those who started off most worried about their exam results.