It's an ironic reality that misery spirals downwards. Or, put another way, most often you get what you expect. But who knew this also applied to wellness?

Now a new study from Harvard adds weight to the proposition that optimists are healthier. Yes, what we think can change not only our daily experiences but our long-term health outcomes.

Here's the science: researchers have found that optimism has a significant association with a decreased risk of death from cancer, heart disease, stroke, respiratory disease and infections. The study, Optimism and Cause-Specific Mortality: A Prospective Cohort Study, published recently in the American Journal of Epidemiology, questioned more than 70,000 women. To satisfy sceptics who would point out the results would be affected by smoking or excessive drinking, the they were asked not only to rate their optimism but about their educational and socioeconomic status, tobacco and alcohol consumption, behavioural characteristics and cancer, hypertension and other diseases.

Even after controlling for other health factors, researchers found the most optimistic quartile of women had a nearly 40 per cent lower risk of heart disease and stroke than those in the lowest quartile. The associations with cancer were also significant, although weaker. Take that, all you glass-half-empty types.

It's true that, as early as the 1970s, neuroscientist and pharmacologist Candace Pert, author of Molecules of Emotion, showed that emotions create chemicals in the body that influence cells and even genetic responses – now part of the new science known as epigenetics. But the challenge has been getting the mainstream medical establishment to accept such a proposition, even if most GPs now advocate reducing stress, if not pessimism, especially for Type A personalities.

Yet, as with the Harvard study, the mounting evidence for a little bit of Pollyanna-ism is persuasive.

In 2004, University of California researchers found that the genes of people with high levels of eudemonic happiness – a form of bliss based on meaning or self-realisation – function better by keeping inflammatory gene expression low and antiviral and antibody expression high.

A Dutch study that same year of people aged 65 to 85 found optimism predicted longer life expectancy and a lower probability of heart disease. Another 2004 study, of healthy, middle-aged women, published in the journal Psychosomatic Medicine, observed that in the three years following menopause, heart disease tended to progress more slowly in the optimistic compared with the pessimistic.

This is about more than the power of the mind to improve low mood or negative states, as espoused by the father of positive psychology, Martin Seligman. As the current priestess of holistic medicine, Christiane Northrup, affirms: your beliefs are your biology, with positive thoughts accompanied by positive changes in your body's biochemistry and negative thoughts tending to depress both your mood and your immunity.

While knowledge is power – think positive, be healthier – the infuriating reality is that most of us are working against a natural tendency towards pessimism. We are the glass-half-empty people. Or, as Northrup writes in her book Making Life Easy, the average person thinks about 60,000 thoughts a day, about 80 per cent of them negative and habitual.

But here's news to cheer about: "What we've learnt about the brain is that it gets good at whatever it does the most," she says. "Repetitive thoughts create faster and larger neural pathways in the brain. As the popular axiom goes, neurons that fire together, wire together. The ability of the brain to change its wiring with different thought and movement patterns is known as neuroplasticity. And that quality stays with us for a lifetime, which means that is never too late to change your thought patterns and improve your life."

Surrounding yourself with things you love – whether expensive art, photos of your loved ones, music or fresh flowers – can help boost the feelgood factor.

Meditation may also cheat a pessimistic or stressed brain of its misery fix. MRI scans taken by American researchers in 2013 for a study funded by the National Institute of Health and the Pittsburgh Life Sciences Greenhouse Opportunity Fund show the brain's "fight or flight" centre, the amygdala, appears to shrink after an eight-week course of mindfulness practice. The result is the pre-frontal cortex – associated with higher-order brain functions including awareness, concentration and decision-making – thickens and disappointing or calamitous events, such as losing a crucial business deal, have less impact on your emotional state.

In the health and happiness stakes, what you don't do is also important. Cutting down on violent or depressing media – the news, crime shows, horror films – and avoiding pessimistic people will pay immediate benefits.

So too will working less or doing less – a radical suggestion in our multi-tasking corporate arena – giving the body and mind time to rest and reset, especially if that time is filled with pleasurable activities.

Of course being more optimistic creates its own wellness cycle. People who are in good spirits tend to have a better diet, exercise more often and get better sleep than those who are not. This could be, in part, because leading a healthy lifestyle helps you kick goals, leading to greater happiness.

Finally, if you can't manage optimism, then at least lean towards its sister-in-wellness, altruism.

In 2005 Dr Dennis Charney, dean of the Icahn School of Medicine at Mount Sinai in New York City, studied 750 Vietnam veterans who had not developed depression or post traumatic stress disorder after being held prisoners of war to see what might have protected them from extreme stress.

After extensive interviews and tests, he concluded that the top trait that set them apart was optimism. The second was altruism.

Perhaps this is why volunteering, something that distracts you from your own misery, is often suggested as a shortcut to increasing gratitude and, ultimately, happiness and good health.