Heavy Manual Labor, Not Leisure-Time Exercise, Tied to AF Risk

Marlene Busko

July 28, 2016

COPENHAGEN, DENMARK — Having a job that requires frequent heavy lifting or working with arms above shoulder level was linked with an increased risk of developing atrial fibrillation (AF) in a 20-year follow-up of people in the Copenhagen City Heart Study (CCHS), researchers report[1]. In contrast, being sedentary, exercising a little to a lot in leisure time, or doing less physically demanding work did not up the risk of AF.

These findings, by Dr Ane K Skielboe (Hvidovre Hospital, Denmark) and colleagues, from one of the first studies to look specifically at work-related physical activity, was published online July 18, 2016 in the European Journal of Preventive Cardiology.

"High occupational physical activity wears the musculoskeletal system; in this study we have shown that it also wears the heart by increasing the risk of atrial fibrillation," Skielboe told heartwire from Medscape in an email. However, further studies are needed to better understand the biological mechanisms behind this.

"It's preliminary evidence," Dr Kevin Monahan (Boston Medical Center, MA) who wasn't involved with the study, commented to heartwire . "It kind of opens the door to a new way of thinking about activity."

Clinicians need to be aware that patients may have very physically demanding jobs, which may affect their heart health. "There may be some risk of AF in those people with very demanding jobs, and of course there are some confounders," he said. "For that reason, it's a very well-done preliminary trial that raises some questions."

Leisure-Time vs Work-Related Physical Activity and Risk of AF

Previous studies in nonathletes have reported that leisure-time physical activity increases, decreases, or has no effect on incident AF, and studies in elite athletes suggest that vigorous physical exercise ups this risk, but this is still controversial, according to Skielboe and colleagues.

To their knowledge, only one study evaluated the link between occupational physical activity and onset of AF, and it found no association.

Thus, they examined data from 17,196 men and women aged 20 and older, living in Copenhagen, and free of AF when they entered the CCHS in 1976–1978. The participants were examined again in 1981–1983, 1991–1994, and 2001–2003.

Based on their replies to a physical-activity questionnaire, they were classed into four levels of leisure-time physical activity:

  • Low: reading, watching television, walking, or biking or low level activity <2 hours/week.

  • Moderate: light physical activity for 2 to 4 hours/week.

  • High: light physical activity for >4 hours/week, or more vigorous activity (eg, brisk walking, fast biking, intense gardening, energetic sports) for 2 to 4 hours/week.

  • Very high: very vigorous physical activity for >4 hours/week or intense exercise/competitive sports several times a week.

They were also classed into four levels of occupational physical activity:

  • Low: mainly sedentary (eg, office work).

  • Moderate: quite a bit of walking, no heavy lifting.

  • High: walking most of the time (often up stairs), some lifting (eg, mail delivery, construction work).

  • Very high: heavy physical labor (eg, digging, shoveling).

Roughly 2000 to 3500 men and women reported that their work involved low, moderate, or high levels physical activity. Fewer men (949) and hardly any women (39) reported doing very heavy physical labor.

During a mean follow-up of 20.3 years, 1192 participants developed AF.

There was a J-shaped relationship between work-related physical activity and AF.

Compared to men with the least physically demanding jobs, those with the most physically demanding jobs were around the same mean age (47), but they were more likely to be heavy smokers (>15 g/day tobacco; 56%% vs 39%) and drink alcohol daily (53% vs 31%) and less likely to have more than 10 years of schooling (5% vs 46%).

None of the few women who had very physically demanding jobs developed AF.

After adjustment for confounders, the risk for AF was much higher in participants with high or very high levels of occupational physical activity.

Risk of Incident AF, High or Very High vs Moderate Occupational Physical Activity*

Occupational Physical Activity HR (95% CI) P
High 1.21 (1.02–1.43) 0.028
Very high 1.39 (1.03–1.88) 0.034
*Adjusted for age, height, body-mass index, sex, smoking, alcohol consumption, education, blood pressure, resting heart rate, spirometry, cardiac medication, type 2 diabetes, ischemic heart disease, and enrollment number

The results were similar in a subanalysis of participants who were younger than 68 (the typical retirement age in Denmark).

There was no significant association between levels of leisure-time activity and risk of incident AF.

"At first, it surprised us that high leisure-time physical activity wasn't associated with the expected increased risk of AF, but when reconsidering, it was very well explained by our study design," Skielboe said. "The volume of physical activity, although characterized by being very high, still does not correspond to the volume of physical activity performed by elite athletes," she said. One of the takeaways is that "leisure-time physical activity on a nonelite level is safe in relation to the risk of AF," according to the researchers.

In the meantime, it is important not to overinterpret the data, because this is an observational study, Monahan cautioned. As the authors also concede, people tend to overestimate their level of leisure-time physical activity. Also, other confounding factors may be involved. For example, people were not asked to report how many alcoholic drinks/day they consumed, and the manual laborers probably had an overall less healthy lifestyle.

The authors had no relevant financial relationships.

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