Exercise to Prevent High BP, Even in Relatively Polluted Areas

Megan Brooks

July 21, 2020

Regular physical activity helps reduce the risk for high blood pressure, even in areas with significant air pollution, according to a longitudinal study from Taiwan.

Although high physical activity combined with lower air pollution exposure was associated with a lower risk for high blood pressure, physical activity continued to have a protective effect even when people were exposed to higher levels of air pollution.

"The research findings of our study indicate that regular physical activity is a safe approach for people living in relatively polluted regions to reduce the risk of hypertension and should be promoted even in polluted areas," Xiang Qian Lao, PhD, Chinese University of Hong Kong, told theheart.org | Medscape Cardiology.

The study was published online July 20 in Circulation.

Physical activity increases the rate of ventilation and it may also increase the intake of air pollutants, which may exacerbate the harmful health effects caused by air pollutants, Lao explained. However, some studies have shown that physical activity protects against the harm caused by air pollution or is independent of air pollution.

The researchers examined the joint associations between regular physical activity and long-term exposure to fine particulate matter (PM2.5) with the development of hypertension in 140,072 normotensive adults in Taiwan, where the annual PM2.5 concentrations exceed the limit recommended by the World Health Organization (WHO).

The participants (mean age, 42 years; 49% men) underwent standard medical screenings between 2001 and 2016, with follow-up lasting 5 years on average. The researchers obtained information on physical activity and other variables from a self-administered questionnaire and individual PM2.5 exposure from satellite data.

PM2.5 exposure was categorized into tertiles: low (mean, 20.0 μg/m3), moderate (mean, 24.1 μg/m3), and high (mean, 34.4 μg/m3).

Mean systolic blood pressure (BP) was 112.5 mm Hg and mean diastolic BP was 68.7 mm Hg. The mean PM2.5 concentration was 26.1 μg/m3 (range, 5.7 μg/m3 to 50.3 μg/m3).

More than a third (34%) of participants were inactive (metabolic equivalent values-hours = 0, no habitual physical activity), 30% reported moderate physical activity (up to 8.75 MET-h), and 36% reported high levels of physical activity (>8.75 MET-h).

The health outcome of interest was incident hypertension (systolic BP ≥140 mm Hg, diastolic BP ≥90 mm Hg, or self-reported physician-diagnosed hypertension).

After adjustment for a wide range of covariates, including PM2.5, a higher level of physical activity was associated with lower risk for hypertension (moderate activity vs inactivity hazard ratio [HR], 0.93 [95% CI, 0.89 - 0.97]; high activity vs inactivity HR, 0.92 [95% CI, 0.88 - 0.96]).

A higher level of PM2.5 was associated with greater adjusted risk for hypertension (moderate vs low HR, 1.37 [95% CI, 1.32 - 1.43]; high vs low HR, 1.92 [95% CI, 1.81 - 2.04]).

However, there was no significant interaction between levels of habitual physical activity and PM2.5 (HR, 1.01; 95% CI, 1.00 - 1.02).

Analyses based on the tertile categories suggest that the association between hypertension and PM2.5 exposure was stronger than that between hypertension and habitual physical activity (PA), the authors note. Each categorical increment in PM2.5 was associated with a 38% higher risk for incident hypertension, whereas each categorical increment in PA was associated with a 6% lower risk for hypertension. Similar patterns were observed in stratified analyses.

"These results suggest that air pollution mitigation may be more effective in preventing hypertension compared with habitual PA," they write.

More than 91% of the world population currently lives in areas where air quality does not meet WHO guidelines, Lao said. "Thus, health guidelines are urgently needed to inform people living in these regions whether they can benefit from regular physical activity."

The findings also "reinforce the importance of air pollution mitigation for hypertension prevention," he added.

The authors say their findings can't be generalized to other populations with higher exposure to air pollution. Indoor air pollution was not considered in the study; however, cigarette smoking, which is an important source of household air pollution, was a covariate. The study also did not distinguish between outdoor and indoor physical activity, although the vast majority of Taiwanese residents engage in outdoor physical activity.

The study was funded by the Research Grants Council-General Research Fund and the Environmental Health Research Fund of the Chinese University of Hong Kong. The MJ Health Research Foundation in Taiwan provided the health data. The authors have disclosed no relevant conflicts of interest.

Circulation. Published online July 20, 2020. Full text

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