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“OUR minds aren’t passive observers simply observing reality as it is; our minds actually change reality. The reality we experience tomorrow is partly the product of the mindsets we hold today.” That’s what at this year’s World Economic Forum in Davos, Switzerland. It may sound like New Age nonsense, but Crum, who heads the , can back up her claims with hard evidence showing the mysterious influence the mind has over our health and well-being.

Crum’s pioneering research was inspired by her own experiences as a child gymnast and college ice hockey player. “You can be the same physical being from one day to the next,” she says, “but your mindset can have a dramatic effect on performance and physiological capabilities.” She often wondered why. Then, as a psychology student, she read about the placebo effect and had a eureka moment: if our expectations can influence the effectiveness of a drug, perhaps something similar can happen in other situations, too.

Pursuing that idea, Crum and others have discovered that your mindset affects everything from your weight and fitness to the physical toll of insomnia and stress – even how well you age. The upshot is that two people could have identical genes and lifestyles but one can end up healthier than the other, thanks solely to their different thoughts.

Placebos are inert pills used in most clinical drug trials. The participants are divided randomly into two groups: half take the drug being tested, the rest, for comparison, take an identical-looking sugar pill. With no active ingredient, the placebo shouldn’t have any effects. Yet it often brings about measurable changes, triggering the release of natural painkillers and lowering blood pressure, for example – all because of people’s expectations. Patients sometimes reap these benefits even when they know they are taking the placebo (see “Everyday placebos”). On the downside, our , including nausea and skin rashes. This is the placebo effect’s “evil” twin, the nocebo effect (see “The science of voodoo”).

Crum was “blown away” when she learned how powerful these effects can be. “But what surprised me most was the fact that we’ve done relatively little to understand and harness them to improve health and well-being,” she says. Governments spend huge amounts of money encouraging us to adopt healthier lifestyles. What if our efforts could be boosted, or undermined, by the very psychological processes that influence a drug’s efficacy through the placebo and nocebo effects, Crum wondered. She has spent the past decade investigating that possibility.

One of Crum’s first experiments . She suspected that few of them would be aware of the sheer amount of exercise their job entails, and that this might prevent them from gaining the full benefits of that workout. To manipulate their mindsets, she gave half of them detailed information about the physical demands of their work – such as the fact that hoovering burns 200 calories an hour – and told them that their activity met the US surgeon general’s exercise recommendations.

One month later, despite reporting no change to their diet or activity outside work, the cleaners who received the information had lost about a kilogram each, and their average blood pressure had dropped from elevated to normal. The others showed no difference. It was, admittedly, a small study and Crum didn’t record actual behaviour. “It could be that they were putting slightly more oomph into making the beds,” she says.

However, a follow-up study with her colleague, Octavia Zahrt, bolstered the idea that people’s expectations directly influence their body’s response to exercise. That study used data from health surveys monitoring more than 60,000 people for up to 21 years. Zahrt found that the “perceived fitness” of the participants – how they felt compared with the average person – was a than the amount of time they said they spent exercising. Crucially, some of them wore accelerometers for part of the survey period – yet, after taking their actual physicial activity into account, the influence of their perceived fitness remained. Overall, people who took a more pessimistic view of their fitness were up to 71 per cent more likely to die during the survey, compared with those who thought they were more active than average – whatever their exercise routine.

How this works is still a bit of a mystery. We do know that the brain can directly control blood pressure through the autonomic nervous system. In addition, Crum suspects that a poor perception of your fitness could be triggering inflammation and the release of hormones such as cortisol, which might help determine how the body responds to exercise. Her team is investigating possible mechanisms but, she says, it’s not too early to take advantage of these effects. Crum’s advice, which she follows herself, is not to deceive yourself about your fitness, but to make sure that you don’t undervalue the exercise you do either. You should also avoid comparing yourself critically with your peers, particularly if they are exceptionally sporty.

Fabrizio Benedetti at the University of Turin Medical School, Italy, who has pioneered work on the placebo and nocebo effects, praises the findings. “Crum’s work is very interesting and her approach to health is important from both a medical and psychological point of view,” says Benedetti. He stresses the need for caution, given the many variables that influence everyday fitness, but argues that “we can learn a lot about the mechanisms, implications and applications” of the mind-body connection from such studies.

Crum has now documented many other ways in which our mindset could be harming our health. A nocebo effect may undermine efforts to lose weight by dieting, for instance. In 2011, Crum , then measured their levels of the “hunger hormone” ghrelin, which normally drops after a meal. Although everyone received the same shake, some were told it was healthy while others were led to believe they were having an indulgent treat. The impact was striking. Those who thought they had drunk a low-calorie shake showed markedly higher levels of ghrelin afterwards, which left them feeling less full.

“Understanding that stress needn’t be damaging can help your body cope with it”

Ghrelin doesn’t affect appetite alone. By signalling food deprivation, the hormone also slows down metabolism, tipping the body towards storing fat rather than burning it. It makes evolutionary sense to reduce energy consumption when resources are scarce, but it is bad news when we are trying to lose weight. “When people think they are eating healthily, that’s associated with the sense of deprivation,” says Crum. “And that mindset matters in shaping our physiological response.” Instead, she suggests, dieters should cultivate a “mindset of indulgence”, savouring the textures and flavours of whatever they are eating.

Non-dieters could be falling prey to this effect, too. When we drink a sugary beverage, our brain doesn’t seem to recognise the liquid as a source of energy, and so that we tend to eat more afterwards than if we had eaten solid food containing the same number of calories. However, it is possible to subvert this effect by changing our expectations. Richard Mattes at Purdue University in Indiana primed people to believe that an energy drink would solidify once it reached their stomach. As well as lowering ghrelin levels, this increased their insulin response after consumption, and the drink stayed in their stomach longer – . “That was followed by a decrease in the daily energy they consumed,” says Mattes.

Crum has also been investigating the influence of our expectations on stress. It is well known that , high blood pressure and a compromised immune system. But can the fear of stress itself worsen its harmful effects? To find out, Crum first assessed students’ attitudes by getting them to rate statements such as “experiencing stress depletes my health and vitality” and “experiencing stress enhances my performance and productivity”. Then she told them that they had to give a short presentation. Faced with this prospect, those who considered stress to be debilitating rather than enhancing showed the largest physiological reactions, including greater fluctuations in levels of the stress hormone cortisol.

Such reactions are thought to underpin the most damaging health effects of stress. However, , triggering the production of hormones necessary for cell growth, among other things. “There’s a lot of public health messaging that warns us about the effects of stress, but it’s one-sided, and builds the mindset that stress is debilitating, when in fact there are many enhancing qualities,” says Crum. What’s more, simply understanding that stress needn’t be damaging can help our bodies cope with it. on the ways that stress can boost focus and creativity, Crum’s participants showed , marked by moderate levels of cortisol and raised levels of growth-promoting hormones.

Tired all the time?

The dangers of stressing about stress might help explain some insomnia too. About a quarter of people’s perceptions of how well they sleep don’t correlate with the sleep they actually get, with potentially significant repercussions. “Complaining good sleepers” – people who believe they are insomniacs, even though monitoring of their night-time brain activity suggests otherwise – are most likely to experience symptoms such as daytime fatigue, high blood pressure, depression and anxiety. “Non-complaining bad sleepers”, by contrast, are remarkably free of ill effects. “Worry about poor sleep is a stronger pathogen than poor sleep,” says , who made this discovery.

It is possible that constant daytime fatigue leads people to identify as insomniac, rather than insomnia causing the fatigue. But, that a placebo effect is partly responsible. It found that simply priming participants to think they had slept poorly or unusually deeply influenced their cognitive functioning the next day.

All these findings give us plenty of reasons to reassess our mindsets. But perhaps the most provocative research concerns ageing – with some strong evidence that negative beliefs could knock decades off your life.

. Ellen Langer at Harvard University – who later collaborated with Crum on the hotel cleaner study – took a group of pensioners to a monastery in New Hampshire and told them to act as if they were 22 years younger for the duration of their stay. The retreat was decorated as if the year were 1959, and filled with music, films, magazines and books from that era. Their rooms contained no mirrors, only pictures of their younger selves. After just five days, the pensioners’ arthritis had improved, their posture was more upright, and their thinking – as measured by an IQ test – was sharper.

Inspired by this study, other teams have since shown that our attitudes really can influence how our bodies fare over time. Overall, ageing positively live 7.5 years longer than those who associate it with frailty and senility. Negative perceptions of ageing are not merely the result of poor health; they can by as much as 38 years.

Admittedly, people with a pessimistic view of ageing are less active and less likely to seek healthcare when they need it. However, many studies find this cannot fully explain the effect on health. So, what’s going on?

It seems that people with rosier beliefs about ageing – both of which would mean that they age more slowly. Becca Levy at the Yale School of Public Health has found that – the protective caps at the ends of chromosomes. This matters because telomeres wear away with time, so are a yardstick of age. Such people are also than those who view ageing negatively.

Ageism is deeply engrained. “We know that children as young as 3 or 4 have already assimilated the age stereotypes of their culture,” says Levy. But her latest studies suggest that attitudes can be changed. In one, participants aged between 61 and 99 played a computer game while positive age-related words such as “wise”, “mature” and “experienced” flashed briefly on the screen. Although they did not consciously register the words, their perceptions of ageing had significantly improved after four sessions, as had their physical well-being. Amazingly, the benefits, including increased mobility, .

“It’s about being empowered by the possibility that we can choose better mindsets”

No wonder some researchers are calling for . “Being aware of these stereotypes, and questioning them, and developing a resistance to them – that’s a good skill people can learn at any age,” says Levy.

Of course, a positive mindset is not a panacea. But these findings could help us all benefit more from our efforts to achieve a healthy lifestyle through exercise, a balanced diet, relaxation and getting a good night’s sleep. “It’s about being mindful of the fact that we have mindsets and that they matter, and being empowered by the possibility that we can choose more useful mindsets,” says Crum.

This article appeared in print under the headline “Mind over matter”