A large-scale meta-analysis pooling data from over 50 years of studies and encompassing nearly 200,000 participants suggests that men with jobs that involve a high level of physical activity have a greater risk of early death than those with less active jobs. However, many experts aren't convinced by the study's conclusions, with some suggesting its findings are misleading.

Most experts generally consider physical activity to be a fundamental part of a healthy lifestyle but for some years researchers have noted a strange discordancy in study data. It seems that while physical activity, including voluntary exercise, undertaken as part of a person's leisure time does certainly correlate with beneficial health effects, people engaging in physical activity as part of a day-to-day job tend to suffer more detrimental health consequences. This has been referred to as the physical activity paradox.

An international team of researchers set out to systematically examine decades of evidence behind the correlation. After digging through 2,490 articles, the study ultimately included reliable and relevant data from 17 studies, encompassing 193,696 subjects. The meta-analysis found that men engaging in high-level occupational physical activity had an 18 percent higher chance of early mortality compared with men whose occupations consisted of low-level physical activity.

The study boldly concludes, "The results of this review indicate detrimental health consequences associated with high level occupational physical activity in men, even when adjusting for relevant factors (such as leisure time physical activity). This evidence indicates that physical activity guidelines should differentiate between occupational and leisure time physical activity."

The study's conclusions are proving divisive, with some experts suggesting the analysis suffers from significant methodological limitations. Erika Borkoles from the Queensland University of Technology calls the conclusion "misleading" and points out a significant number of factors that could be contributing to more physical work leading to a higher mortality risk. As well as the study not clearly delineating between different types of job place activities, Borkoles suggests other factors could be at play.

"The causes of death could also be related to occupational stress associated with little control, harsh working conditions, and an overall stress arising from socio-economic backgrounds of the current population," Borkoles says. "Typically, people in such jobs have higher social inequality profiles, indicating less access to paid holidays and sick leave, which threatens their job security if requested."

Stephen Evans from the London School of Hygiene and Tropical Medicine also suggests this kind of study is not granular enough to draw any clear conclusion. He points out the variations in what the study deems "high occupational physical activity" are too broad for a generalized conclusion.

"It could well be that there are some forms of physical activity that are not beneficial, but it is not clear from this paper what they are," says Evans. "Certainly, this paper should not be used to suggest that exercise is not good for health."

Kay-Tee Khaw from the University of Cambridge follows up this concern pointing out the dramatic import of confounding factors, such as social class, education and health behaviors. Khaw also adds that some physical jobs may result in more accidents, leading to higher mortality rates.

"It is quite possible that very heavy labor may be associated with adverse health," says Khaw. "It may also be that these occupations lead to higher accident rates and early mortality without the physical activity itself being the relevant factor which the authors do discuss and I am sure that we need to understand this better."

Ultimately, the authors of this new study do suggest that if their results are found to be causal in further study, they should lead to updated physical activity guidelines that differentiate between occupational and leisure time physical activity. The implication is that strenuous physical activity in a job directly results in a higher mortality rate, but it is currently hard to reach that conclusion considering the large array of alternative factors that are at play.

The new study was published in the British Journal of Sports Medicine.

Source: BMJ via EurekAlert