Simply believing you're doing more exercise than your peers can significantly increase your lifespan according to researchers.

People who think they're less active than others their age actually die younger than those who believe they're more active – even if their activity levels are the same or similar – according to research by Stanford academics Octavia Zahrt and Alia Crum, published in Health Psychology magazine.

"Our findings fall in line with a growing body of research suggesting mindset plays a crucial role in health," explained Crum.

Zahrt and Crum analysed surveys from more than 60,000 US adults, looking at participants' levels of physical activity, health and personal background, asking: "Would you say you're physically more active, less active, or about as active as other people your age?"

They then viewed death records from 2011 (21 years after the first survey was conducted) and after controlling for physical activity and using statistical models that accounted for age, body mass index, chronic illnesses and other factors, found individuals who believed they were less active were up to 71 percent more likely to die in the follow-up period than those who believed they were more active than their peers.

Zahrt and Crum offer some explanations for mindset and perception having such powerful effects. One is the impact on motivation, both positively and negatively, the other is the impact of the placebo effect: "Placebo effects are very robust in medicine. It is only logical to expect that they would play a role in shaping the benefits of behavioural health as well," Crum said.

A growing body of research shows that perceptions and mindsets predict health and longevity when it comes to stress, diet and obesity.

"It's time that we started taking the role of mindsets in health more seriously," Crum said. "In the pursuit of health and longevity, it is important to adopt not only healthy behaviours, but also healthy thoughts."