In a fitness-crazed land of spin classes and CrossFit gyms, Octavia Zahrt found it can be tough to feel as though you're doing enough. "When I was in school in London, I felt really good about my activity. Then I moved to Stanford, and everyone around me seems to be so active and going to the gym every day," she says. "In the San Francisco Bay Area, it's like 75 percent of people walk around here wearing exercise clothes all day, every day, all the time, and just looking really fit."
She wasn't less active than when she lived in London, Zahrt says, but in comparison she began to feel a bit like a slacker. "I felt unhealthy. I was very stressed about fitting in more exercise," she says.
And just feeling less fit in comparison to others might trim away years of life, says Zahrt, a Ph.D. candidate in health psychology at the Stanford University Graduate School of Business. That's the conclusion of a study she co-authored, published Thursday in Health Psychology.
Past studies have suggested that mindsets concerning one's own health can have physiological consequences. In 2007, Stanford psychologist Alia Crum ran a study on hotel attendants. "These women were getting lots of exercise, but when we asked them they didn't have the mindset that their work was good exercise," Crum says.
She gave some of the hotel staff a presentation explaining that their work, which involves heavy lifting and walking, is good exercise, and then tracked them for a month. "The women who started to look at their work as good exercise had improvements in blood pressure and body fat," she says.
Crum and Zahrt collaborated on the new study, which looks at what might happen decades down the line. They analyzed data from two large national health surveys, the National Health Interview Survey and the National Health and Nutrition Examination Survey. Along with a litany of health metrics including activity, weight and smoking status, these surveys also ask participants to assess how much they believe they exercise compared to others their own age.
"Individuals who thought they were less active than other people their age were more likely to die, regardless of health status, body mass index, and so on," Crum says.
That was true even though the researchers looked at people who were roughly the same in every way, including how much they actually exercised based on self-report and step-tracking data, obesity and heart health, except for how much they thought they worked out compared to others.
They analyzed three sets of the survey data, and all three showed people who felt they worked out less than their peers were more likely to die in a 21-year follow-up period than those who felt they exercised more than their peers. In one sample, these people were 71 percent more likely to die. "I was very surprised by the size of [that effect]," Zahrt says. "That there would be an effect on mortality so many years later, that wasn't necessarily obvious to me."
The researchers think there may be a couple of reasons for this. One is simply a type of placebo effect. "What placebo underpins is the effect of our mindset," Crum says. "[For example], the belief you're getting a pain medication can activate endogenous opiates in the brain." Crum thinks something similar may be at play here, where an underlying dread of not exercising enough is a powerful frame of mind that can harm health.
Social comparisons can also be demotivating. "People who think they are less active can be discouraged by that perception, and they might stop exercising and become less active over time," Zahrt says. That subsequent drop in real exercise could account for some of the negative health outcomes the researchers saw in their study.
It's tough to say what's responsible for the study's effect, says Angelina Sutin, a behavioral scientist at Florida State University College of Medicine who was not involved with the work. "We don't have a real grasp on what the mechanism is yet," she says. This study only correlated those who felt they exercised less with higher mortality rates and isn't able to pin down why that might be, Sutin says.
Plus how much you think you exercise is probably still not as important as how much you actually exercise, Sutin points out. Still, she thinks the study is extremely well done. "I thought this was a really nice study and adds a piece of this perception puzzle we're trying to work through," she says.
If Crum and Zahrt are right, and living with the belief you aren't active enough can shorten your life, then their results call into question scare tactics for health messaging. "If you tell people they need to get this really high level of activity or else they have all these healthy complications and die early, you might just be instilling this negative mindset," Zahrt says.
Messaging needs to have accurate information about health and exercise and motivate people to be more active, but doing that without instilling a fear of not exercising can be tricky, Crum says. "The ultimate end goal is the sense of enoughness," she says. "It's all individual. If you're thinking, every day, that you haven't done enough, that is problematic."
ROBERT SIEGEL, HOST:
Here's a pretty simple proposition - people who are more fit on average live longer. It makes sense. Here is a more complex proposition courtesy of a Stanford researcher - people who think they are more fit on average live longer. For this claim on behalf of the power of positive thinking about exercise we are indebted to doctoral candidate Octavia Zahrt at the Stanford University Graduate School of Business. Thanks for joining us today.
OCTAVIA ZAHRT: Thank you for having me.
SIEGEL: How did you actually study the salutary effects of thinking that you're fit as opposed to actually being fit?
ZAHRT: Yeah, well, we looked at three nationally representative surveys where more than 60,000 U.S. adults answered a lot of questions about their physical activity levels, their health and their personal background. And in one of these surveys, they even wore physical activity monitors to measure exactly how much they moved around. And so we were especially interested in one question where they told the interviewer how active they perceived themselves to be compared to other people. And then we used statistical models to see if there is a link between these perceptions and mortality even after accounting for participants' actual health status and actual physical activity. And we did find that there was a strong correlation between perceptions and mortality.
SIEGEL: And the correlation that you found, if I understand this, is actually a double negative. That is, there's the power of negative thinking. People who don't think that they're being very fit or being very active, they are more likely to die sooner.
ZAHRT: That is correct, yes. So for any actual level of physical activity that you might be doing, if you think that you aren't getting a lot of physical activity compared to others, you're actually more likely to die earlier than people who think that they're more active or about as active as other people.
SIEGEL: In these cases, we are always reminded of the wisdom that correlation doesn't equal causation, correct?
ZAHRT: That is absolutely correct. And it's a really important point. So this study is correlational. So we can't say that these perceptions actually caused the differences in mortality. But in science, we always say that any one study is not conclusive. So it's really necessary to see it in the context of other studies that have been done. So, you know, the broader literature points to a causal link between mindsets and health, but this particular study doesn't do that on its own.
SIEGEL: But do you think that would work for, say, two people who are equally inert, equally inactive, but one is convinced that he or she is, you know, absolutely - is absolutely engaged in exercise in his or her daily routines? That person might actually be healthier?
ZAHRT: I think that is possible. So the research shows that for any given level of activity, if you think you're getting more exercise, you might be better off. And so that could be mediated by things like, you know, you have less stress and less anxiety about your activity level. And you might even get a sort of placebo effect benefit. But it's important to note that we didn't investigate this question in completely sedentary people, so we can't say for sure. You know, it's possible that you need to get a minimum level of activity to get any benefits. And also, it's really important that - we don't want to advocate for people to stop exercising and replacing exercise with positive perceptions.
SIEGEL: (Laughter) With thinking about exercising.
ZAHRT: Right. So yeah, exercise is definitely important, but we're adding with our research that perceptions also seems to play an important role.
SIEGEL: Octavia Zahrt is a doctoral candidate at the Stanford University Graduate School of Business. Thanks for talking with us today.
ZAHRT: Thanks so much for having me.
SIEGEL: I feel fitter just from talking to you.
ZAHRT: (Laughter) Well, I hope it's helpful.
(SOUNDBITE OF SESSION VICTIM'S "GOOD INTENTIONS") Transcript provided by NPR, Copyright NPR.