While physical activity can lower the risk of heart disease, two studies suggest that jobs involving hard manual labor may harm, rather than help the heart.
Presenting at the annual EuroPRevent 2013 meeting, two separate groups report on the potential dangers of physically demanding work and provide deeper understanding of how manual labor may differ from a gym workout or a run with respect to the heart.
The first, from researchers at Harokopio University in Athens, involved 250 first-time stroke patients, 250 patients who experienced their first heart event, and 500 healthy controls, all of whom ranked their jobs on a scale of how physically demanding they were. Those reporting more labor-intensive occupations showed higher rates of heart events; for each one unit drop in the ranking of physical intensity, the participants showed a 20% decline in their chances of having a heart event. The association held even after the researchers adjusted for possible heart disease risk factors such as sex, BMI, smoking, diabetes and diet.
A second study conducted by researchers from the Department of Public Health at the University of Ghent in Belgium found similar evidence that physically demanding labor could increase risk of heart problems, particularly among those who also exercised during their leisure time. The trial, involving a cohort of over 14,000 middle-aged men without heart disease, provided more details about how occupational and leisure activity might interact. The participants answered questions about their jobs, heart health and any physical activity they did for leisure between 1994 and 1998.
After following the men for slightly more than three years on average, the researchers found that those with jobs involving lower levels of physical labor who also engaged in moderate to intense leisure-time activity enjoyed a 60% reduced risk of heart events. But men whose jobs were more physically demanding and who also exercised when they were off the clock showed a nearly 70% increased risk of heart problems. After adjusting for other factors that could contribute to heart disease risk, the men with the physically demanding jobs were more than four times likely as those with less physically-oriented occupations to develop heart disease if they also exercised regularly.
“The hypothesis based on our study and other recent literature is that physical activities done on the job usually include more static activity types which do not have a training effect on the cardiovascular system, but have an overloading effect on the system,” says study author Dr. Els Clays. Jobs that require activities like heavy lifting, awkward postures and high physical exertion are known to increase blood pressure and heart rate. “If people are exposed to that for a long time, like multiple hours during the day, that can really have an adverse effect on their cardiovascular health,” says Clays.
Jobs that demand a lot of heavy lifting appear to be more taxing on a body in a way that doesn’t benefit health like going for a run, according to Clays. The researchers of the first study also suggest that the stress accompanying physically demanding jobs may counteract the positive effects of exercise. It’s also possible that those with physically draining jobs may have less access to health care; such occupations generally involve manual labor and often pay less and provide limited health insurance. With less access to preventive health therapies, rates of chronic conditions such as heart disease may be higher.
The findings reinforce the complex relationship between physical activity and heart disease, and suggests that doctors should take into account the types of physical activity people do in different settings. “There is increasing evidence in recent years showing occupational demands do not have the beneficial effect general physical activity has. This study really confirms that,” says Clays. “The basic message is we really need more detailed measures for physical activity.”