Paper Probes Physical Activity Paradox and Perils of ‘Privileged’ Advice

Keeping physically active as part of a healthy lifestyle matters for cardiovascular health, but new insights from the large Copenhagen General Population Study hint that while leisure-time exercise lowers the risk of major adverse cardiovascular events, occupational physical activity actually has the opposite effect.

The findings, write Andreas Holtermann, PhD (National Research Centre for the Working Environment, Copenhagen, Denmark), and colleagues, support the view that the two types of physical activity actually interact independently on risk of MACE and all-cause mortality, supporting the notion of a “physical activity paradox.”

Holtermann, in an interview with TCTMD, said that he first became aware of the paradox when he started working with labor unions more than 10 years ago. There, it was clear that people in manual-labor jobs, particularly in developed nations, did not seem to derive any benefits from working long days that involved constant walking, lifting, or higher energy expenditure and, indeed, were dying 10 to 15 years earlier than their white-collar counterparts.

Moreover, CVD prevention guidelines recommend that everyone engage in daily physical activity, but that guidance stems from studies of more-“privileged” populations in sedentary jobs and doesn’t necessarily make sense for people doing active jobs, Holtermann explained. Research that has looked at people doing manual labor in the modern era is relatively rare and “showed either increased risk for cardiovascular disease mortality, or all-cause mortality, or at least did not see the health benefits that we see consistently from leisure time physical activity,” Holtermann said.

There’s a pressing need, he argued, for physical activity studies in populations representing more diverse socioeconomic and racial/ethnic backgrounds.

“My biggest concern is that most of the research that has been done on physical activity up to now, if you look at the big studies, has been done in white-collar, privileged people. In how many construction workers do you think we have data on, in the world, for physical activity? Very few. They don't participate in the studies. I think we have beautiful evidence, and I don’t doubt it whatsoever, that for those of us having sedentary work we need to exercise,” he continued. “But we don’t have evidence for those high-risk groups often having these blue collar, risky jobs.”

The results were published earlier this month in the European Heart Journal.

Activity Type Matters

Holtermann and colleagues examined 10-year follow-up among 104,046 men and women age 20-100 in the Copenhagen General Population Study, who provided information on leisure and occupational physical activity at study entry. After adjusting for self-reported lifestyle factors, health indices, living conditions, and socioeconomic aspects, the investigators observed an inverse dose-response relationship between increasing levels of leisure time physical activity (also self-reported) and reduced risk of both MACE and all-cause mortality.

For occupational physical activity, by contrast, increasing levels of physical activity tracked in parallel with increased risk of MACE and all-cause mortality.

Risk by Physical-Activity Type and Intensity Level: HR (95% CI)

As the authors point out, the strong association between increasing levels of leisure-time physical activity and reduced MACE and all-cause mortality is in line with “many” previous studies. Likewise, the harmful association between increasing occupational physical activity and MACE/outcomes has been seen in some—but not all—studies. Both sets of findings have typically been criticized for not adequately controlling for confounding factors—something the authors in the current study devoted considerable attention, Holtermann stressed to TCTMD. They conclude: “These findings may be considered by those writing guidelines on cardiovascular disease prevention in relation to physical activity.”

Some Caveats

In an editorial accompanying the study, Martin Halle, MD, and Melanie Heitkamp, PhD (both Technical University of Munich, Germany), point out that most of the data informing physical activity guidelines stems from stems from observational studies, opening up the findings to selection and information bias. The present one is no exception. But what’s clear, Halle told TCTMD, is that physical exercise differs between settings.

“We need to go deeper in this field,” Halle observed. “This [study] clearly shows that physical activity is not the Holy Grail, that it is very, very important but maybe when it's done in leisure time it's better than being done in an occupational setting.”

Speculating on the seemingly contradictory findings, Halle and Heitkamp propose that leisure-time activity is typically more aerobic, involving more endurance exercise, whereas occupational exercise more typically involves resistance exercise in short bouts, with insufficient recovery time. Occupational activity may also come with psychological factors or environmental stressors less common in sedentary work, that negatively impact health.

Holtermann’s take was slightly different: that leisure time activities are typically shorter, whereas occupational activities require effort expenditure over the entire day (or night). Speaking with TCTMD, he put particular emphasis on the lack of control during work-time activities and the specific physiological stressors that might entail.

For example, a person going for a walk or a run at the end of a sedentary day would experience higher heart rate and blood-pressure levels for that period of activity, but these would drop to normal after the 30- or 60-minute period of exercise. Moreover, the leisure-time exerciser could stop or slow down if the effort became too much.

By contrast, said Holtermann, a person working in a cleaning job requiring constant steps, lifting, and use of force would have lesser heart rate and blood pressure elevations that were sustained over a much longer, potentially unhealthy period of time, without the option of slowing or stopping. In Holtermann’s opinion, there are “plausible physiological mechanisms” that are potentially operating on top of the socioeconomic risk factors already prevalent in populations typically working in manual labor jobs.

PURE Pushback

One of the largest analyses to address the impact of physical activity across populations comes from the massive Prospective Urban Rural Epidemiology (PURE) study. As reported by TCTMD, the 2017 study, published in the Lancet, suggested that activity of any type—recreational, occupational, domestic, or otherwise, across a range of countries and economies—all helped to lower the risk of cardiovascular disease and death over a median follow-up of nearly 7 years.

Speaking with TCTMD, Scott Lear, PhD, who led the PURE analysis, disagreed with Holtermann et al’s conclusion that types of activity might exert independent effects on cardiovascular health. “I'd have a hard time with that,” he said. “For most people, the body doesn't care what we call the activity. [Instead] the body cares about the intensity and the duration of the activity, and some people's other health circumstances may put them in a situation where not every type of activity is going to be helpful for them.”

Like Holtermann, Lear points to control as being a key differentiating factor. In an occupational environment where the worker can’t take a break or can’t work at a heart rate that is healthful and not harmful, that could lead to adverse effects, he suggested.

In recent years, a number of CVD prevention advocates and guidelines have taken the position that “every step counts” for ideal health—a position Halle and Heitkamp maintain in their editorial, despite the “paradox” described by Holtermann and colleagues.

“This is still our recommendation,” Halle clarified to TCTMD. “But secondly, intensity counts, and third, the environment also plays an important role, and this is not only diet but what environment we have at work,” a notion that takes into account air quality and work hours. “So the global message is yes, the workplace is a great place to increase physical activity and it is certainly the worst place for cardiovascular risk because of sitting and because of stressful work,” he explained.

What matters now is for employers to take this information and think of ways to improve the work environment. “And that's not just by increasing physical activity as an anti-stress intervention,” Halle said. “We should have a closer look at nightshifts, a closer look at easing the work of workers when it is physical work, we should reduce stressors and psychological stress and improve nutrition so it is a clear message to companies to modify their health approaches for their workers.”

More-Focused Studies

For Holtermann, improving the work environment means understanding the specifics of the work itself and acknowledging the socioeconomic, ethnic, and racial realities that underpin this research. Attributing the lack of benefit seen with occupational activity in manual labor and lower income jobs to factors like smoking, obesity, diet, low education levels, etc, doesn’t go far enough.

“What I see as problematic is that a lot of researchers are saying, ‘Well, it's just confounding so just forget about it.’ But I'm just saying, what if it’s not? What if it's actually true that they are at increased risk from their jobs and we have just for all time said oh, it's just confounding. That's the reason why I'm saying we have sufficient evidence on physical activity and health for sedentary jobs and privileged people, but we need more research on this group.”

His hope, said Holtermann, is that more studies like this can lead to better recommendations and better insights. He and his colleagues are currently doing a much larger study using accelerometers to more accurately measure physical activity rather than rely on self-reported data and all of the problems that entails.

Telling a person who has worked in a taxing, manual job all day long that they also need to find a way to squeeze in 30 minutes of aerobic activity, based on studies primarily of white-collar workers, is not appropriate, he said. Instead, his “dream,” is to find evidence-based ways of “making the work of less-privileged, manual workers more health-promoting,” potentially by varying the activities and level of output throughout the day, or by allowing more time for breaks and heart rate variation.

Holtermann has already secured the funding for the project and hopes to get the study underway when the COVID-19 crisis is past.