Many of us accept we're not the healthiest person on the planet.

But new research warns this mindset could be dangerous.

In fact, according to Stanford University, people who view themselves as less healthy than others are at risk of suffering a premature death - no matter how active they actually are.

The study, published in Health Psychology, is the latest of many to show how our thoughts, feelings and beliefs have a direct impact on our health.

Experts say this shows we should equally prioritize feeling positive and working out.

Stanford University researchers tracked 60,000 Americans over 21 years. They found those who saw themselves as less physically active were 71 percent more likely to die early (stock)

'Our findings fall in line with a growing body of research suggesting that our mindsets - in this case, beliefs about how much exercise we are getting relative to others - can play a crucial role in our health,' co-author Dr Alia Crum said.

Dr Crum, an assistant professor of psychology, and Octavia Zahrt, a doctoral candidate at the Graduate School of Business, analyzed surveys from more than 60,000 U.S. adults from three national data sets.

The surveys documented participants' levels of physical activity, health and personal background, among other measures.

In one of the samples, participants wore an accelerometer to measure their activity over a week.

They were all asked the same question: 'Would you say that you are physically more active, less active, or about as active as other persons your age?'

The researchers then viewed death records from 2011, which was 21 years after the first survey was conducted.

They found that people who saw themselves as less active than others were up to 71 percent more likely to die in the follow-up period than people who thought they were more active than their peers.

This was even true after they controlled for physical activity, age, body mass index, chronic illnesses and other factors.

Dr Crum's prior research shows that the health benefits people get out of everyday activities depend in part on their mindsets - that is, whether or not they believe that they are getting good exercise.

In her 2007 study, Dr Crum told a group of workers at a hotel that the activity they got at work met recommended levels of physical activity.

Previously, most of the workers had seen themselves as inactive.

Through this shift in mindsets, the workers experienced reductions in weight, body fat and blood pressure, among other positive outcomes.

Zahrt and Dr Crum offer possible explanations for mindsets and perceptions having such powerful effects on health. One is that perceptions can affect motivation, both positively and negatively.

Those who are made aware of their healthy activity levels - like the hotel room attendants in Dr Crum's 2007 study - can build on them and exercise more.

Those who deem themselves unfit are more likely to remain inactive, fueling feelings of fear, stress or depression that negatively affect their health.

The researchers also cite the established influence of placebo effects, where patients who think they are getting a treatment experience physiological changes without receiving actual treatment.

In the same way, people who believe they are getting good exercise may experience more physiological benefits from their exercise than those who believe they aren't getting enough exercise.

'Placebo effects are very robust in medicine. It is only logical to expect that they would play a role in shaping the benefits of behavioral health as well,' Dr Crum said.

The researchers emphasize that the study is correlational in nature and thus does not prove that perceptions of inactivity cause earlier death. However, other experimental research - such as Dr Crum's 2007 study - does suggest a causal nature to the link between perceived amounts of exercise and health outcomes.

'So much effort, notably in public health campaigns, is geared toward motivating people to change their behavior: eat healthier, exercise more and stress less,' Dr Crum said. 'But an important variable is being left out of the equation: people's mindsets about those healthy behaviors.'

In fact, a growing volume of research from Dr Crum and other labs shows that perceptions and mindsets predict health and longevity, for example, in the domains of stress, diet and obesity.

It seems unlikely. But Dr Crum insists it is not surprising, considering the 'everyday experiences where our beliefs or a simple thought have very palpable and physiological effects.'

'In the case of stress, a thought about something going wrong can make us sweat or [become] shaky or increase our heart rate,' Dr Crum continued.

'With sexual arousal, a simple thought or idea can have immediate physical effects.

'We experience these things regularly, and yet we're not cataloguing them as something that matters.

'For whatever reason - dualism or a prioritization of the material - we tend to ignore the fact that our thoughts, mindsets and expectations are shaping our everyday physiology.'

Zahrt and Dr Crum say the findings could help change our perception that vigorous exercise in a gym is the only way to attain a proper activity level.

Being mindful of and feeling good about activities you do every day - like taking the stairs, walking or biking to work, or cleaning the house - could be an easy first step for everyone to benefit their health, they say.

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