Actively commuting to work lowers risk of IHD, stroke

A study of more than 100,000 urban commuters in China suggests that walking or cycling to work can lower people’s risk of ischemic heart disease (IHD) and stroke, even when factoring in the “rather serious air pollution” in the country.

Mengyu Fan, PhD, of Peking University Health Science Center in Beijing, and colleagues reported in the Journal of the American Heart Association that although the majority of workers in China commute to work passively—by car, for example—those who engaged in active commuting saw greater health benefits. But while it’s easy to advocate for active commuting as a way to boost CV wellness, people in China have to consider another health risk: air pollution.

Fan et al. wrote that a recent study of 263,540 individuals enrolled in the UK Biobank found cycling and walking to work were associated with a lower risk of CVD, but those authors didn’t adjust for overall non-community activity level and failed to differentiate between cardiovascular endpoints. And data from U.K. patients can’t necessarily be applied to other non-white populations—especially if those populations deal with persistent pollution in their communities.

It’s been estimated that more than 95% of the Chinese population was exposed to higher-than-acceptable levels of fine particulate matter and nitrogen dioxide in 2015, and one study published this year suggests residents’ risk of a higher coronary artery calcium score increased by 24.5% per 20 micrograms per cubic meter of air increase in nitrogen dioxide. 

Considering that 40% of all global deaths can be attributed to CVD, the implications of toxic air pollutants in China could be fatal.

Fan and colleagues studied 104,170 urban commuters enrolled in the China Kadoorie Biobank for their study, none of whom had a major chronic disease at baseline. Participants self-reported their commuting mode, choosing from either non-active commuting, working at or near home, walking or cycling.

Nearly half—47.2%—of subjects reported non-active commuting, the authors said. An additional 13.4% reported working at or near home, 20.1% said their walked to work and 19.4% reported cycling. During a decade of follow-up, Fan et al. logged 5,374 incidents of IHD, 664 cases of hemorrhagic stroke and 4,834 cases of ischemic stroke.

After adjusting for a number of factors, including sex, socioeconomic status, lifestyle variables, sedentary time, BMI, comborbidities, household air pollution, passive smoking and other physical activities, walking to work was linked to a 10% reduced risk of IHD and cycling was associated with a 19% reduced risk of IHD compared to non-active commuting.

Cycling was tied to an 8% lower risk of ischemic stroke, but the authors didn’t find any relationship between walking or cycling and risk of hemorrhagic stroke. Results were consistent between men and women.

“Existing literature on active commuting mainly focused on CVD, coronary heart disease and cardiovascular risk factors,” Fan and co-authors wrote. “Our finding that active commuting was associated with a reduced risk of IHD was in agreement with these studies. The risk reduction was  larger in the cycling group than in the walking group, reflecting the greater physiological intensity of cycling compared with walking.”

The fact that activity was self-reported means the team’s study is subject to bias, and their results were specific to an older population in China. Therefore, their findings can’t necessarily be extrapolated to other situations.

“Although we have adjusted for multiple confounding factors, residual confounding, particularly socioeconomic status, was still possible,” the authors wrote. “However, active commuting was associated with low socioeconomic status in this study population. Our findings provide direct support for policies that encourage adults to participate in active commuting to deliver health benefits at the population level.”