Low activity, high PM2.5 exposure increased diabetes risk in study

Regular exercise appears to be protective against type 2 diabetes, even when exercise occurs in areas with high air pollution levels, according to findings from a longitudinal cohort study conducted in Taiwan.

No significant interaction was found between regular exposure to air pollution (<2.5 μm PM particles [PM2.5]) and regular physical activity with regard to diabetes incidence among the adults in the study living in relatively polluted areas.

The protective effect of regular exercise did not appear to be significantly altered by levels of PM2.5 exposure in the study, which was the first longitudinal investigation of the impact of regular exercise and regular exposure to air pollution on type 2 diabetes risk at the population level.

Low levels of physical activity combined with high levels of PM2.5 exposure were associated with a significantly higher risk for developing type 2 diabetes in the study, Xiang Qian Lao, of the Chinese University of Hong Kong, Guangdong, China, and colleagues reported in the European Association for the Study of Diabetes (EASD) journal Diabetologia.

“Our study supports the notion that habitual physical activity is beneficial for diabetes prevention, even for people residing in relatively polluted areas, but also reinforces the importance of air pollution mitigation for diabetes prevention,” Lao and colleagues wrote.

Regular physical exercise has been shown to be strongly protective against cardiovascular disease, type 2 diabetes, and other chronic diseases in numerous studies. However, aerobic outdoor activity is also associated with increased inhalation of air pollution, which is associated with increased risk for the same chronic diseases.

“The risk-benefit relationship between air pollution and physical activity has become an important public health concern as more than 91% of the world’s population lives in places where air quality does not meet the WHO guidelines,” the researchers wrote.”…Health guidelines are urgently needed, especially in regions with significant air pollution, to inform people whether they can benefit from habitual physical activity.”

The longitudinal study was designed to examine the combined impact of chronic exposure to particulate matter with an aerodynamic diameter less than 2.5 μm and regular physical activity on type 2 diabetes incidence.

The study included 156,314 non-diabetic adults (≥18 years old) who joined the ongoing longitudinal cohort between 2001 and 2016. Two-year mean PM2.5 exposure was estimated at each participant’s address using a satellite-based spatiotemporal model. Information on physical activity and significant covariates was collected using a standard self-administered questionnaire.

Data analysis included Cox regression modeling with time-varying covariates. An interaction term between PM2.5 and physical activity was included to examine the overall interaction effects.

PM2.5 concentrations were generally comparable among the participants with different categories of habitual physical activity. The mean duration of follow-up was 5.2 years (SD of 3.6 years).

In all, 5,305 new cases of type 2 diabetes were identified with an incidence rate of 6.53 per 1,000 person-years. The participants underwent a median of three medical examinations (range, 2–26) during the study period.

The contrast in PM2.5 exposure was large (range 6.38– 49.78 μg/m3; overall IQR 21.80–28.07 μg/m3). PM2.5 concentrations peaked in 2004 and declined gradually in the following years.

Not surprisingly, high habitual physical activity was associated with a lower incidence of type 2 diabetes, and high chronic PM2.5 exposure was associated with a higher incidence.

“Mutual adjustment generally resulted in slight change in the associations,” the researchers wrote. “Overall, the concentration-response curve was approximately linear (likelihood ratio test: χ2 = 2.8, P=0.09). No significant interactions were observed (P=0.52).

Compared with high physical activity, moderate and inactive/low physical activity were associated with a higher risk of diabetes (HR, 1.31; 95% CI, 1.22-1.41 and HR 1.56; 95% CI, 1.46-1.68, respectively).

Study participants with moderate or high PM2.5 exposures had a higher risk of type 2 diabetes than the participants exposed to low PM2.5 (HR 1.31; 95% CI, 1.22-1.40] and HR 1.94; 95% CI, 1.76- 2.14, respectively).

Participants with high physical activity and low PM2.5 had a 64% lower risk of type 2 diabetes compared to those with inactive/low physical activity and high PM2.5.

A significant study limitation cited by the researchers was the failure to distinguish between physical activity occurring indoors and outdoors.

“However, a 2017 national survey showed that 92.7% of Taiwanese residents reported outdoor physical activity,” they wrote.

Another limitation involved the reliance on self-administered questionnaires to assess physical activity levels.

The researchers noted that more study is needed to fully explain the interaction between regular physical activity, chronic PM2.5 exposure, and type 2 diabetes risk.

Lao et al cited a previously published study involving bicycle riders which suggested that pollutants inhaled during exercise make up only a small fraction of total inhaled air pollutants. “This may partly explain the positive associations between physical activity and type 2 diabetes regardless of the levels of PM2.5 exposure,” they wrote. “Moreover, the long-term benefits of habitual physical activity may reverse the acute adverse effects associated with the additional intake of air pollutants during exercise.”

  1. Regular exercise appears to remain protective against type 2 diabetes even in areas with high air pollution levels, according to findings from a longitudinal cohort study conducted in Taiwan.

  2. The protective effect of regular exercise did not appear to be significantly altered by levels of PM2.5 exposure in the study.

Salynn Boyles, Contributing Writer, BreakingMED™

Funding for this research was provided by RGC General Research Fund and the Environmental Health Research Fund of the Chinese University of Hong Kong.

The researchers declared no relevant conflicts related to this study.

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