Exposure to air pollution contributes to higher BP, hypertension

For a major part of north India, air pollution is a menacing issue and last year during the winter season, pollution led to a health emergency in Delhi-NCR. Ambient air pollution, specifically PM 2.5, is reportedly associated with cardiovascular disease risk.

However, evidence linking PM 2.5 and blood pressure is largely from cross-sectional studies and from settings with a lower concentration of PM 2.5, with exposures not accounting for myriad time-varying and other factors such as the built environment. But, a first-of-a-kind study in Delhi, has shown epidemiological evidence, for short and long-term effects of ambient PM2.5 exposure on elevated blood pressure(BP) and hypertension.

The research was published in the American Heart Association’s flagship journal Circulation. According to this research, data strongly supports a temporal association between high levels of ambient air pollution, higher systolic BP, and incident hypertension.

One of the authors and lead investigators of the project, Dr. Dorairaj Prabhakaran, vice president, research and policy at the Public Health Foundation India said: “In India, there is very little or no evidence linking the exposure of ambient particulate matter (PM2.5), as a marker of air pollution with hypertension. This is a first-of-a-kind study in the Indian context which shows epidemiological evidence, for short and long-term effects of ambient PM2.5 exposure on elevated BP and hypertension.”

The study was conducted by Indian scientists at the Centre for Chronic Disease Control and PHFI in collaboration with the Harvard T.H. Chan School of Public Health on a locally recruited representative population. It presents strong evidence of the harmful effects of PM2.5 exposures on cardiovascular diseases (CVDs) in India.

“The findings have shown that both short and long-term exposure to air pollution contributed to higher BP and increased risk of hypertension, especially in certain sections of the population (obese individuals),” added Prabhakaran

The research suggests there are significant benefits of controlling air pollution in reducing a major risk factor for cardiovascular deaths, the leading contributor to deaths in the country.

“Till we reach the safe levels of air quality, people with high risk of arrhythmias, worsening heart failure or stroke such as those with severe heart failure should be specially protected by avoiding exposure to high levels of outdoor PM2.5 by not going out on these days or through the use of protective N95 masks if feasible,” said one of the researchers.

The participants in the project were studied for seven years. “The longitudinal range of seven years, over which the participants have been followed, also ensures that we are observing consistent long-term patterns and lends significant weight to the findings compared with cross-sectional studies of intermittent episodes of high pollution and BP that may skew the findings,” said the research.

The authors investigated the association between PM2.5, a marker of air pollution with blood pressure and incident hypertension in Delhi, carried out in a cohort of 5,300 individuals, and included annual questionnaire surveys and alternate year biological sample collection.

Blood pressure was assessed longitudinally at three time points within the cohort over the seven-year period. “There are various mechanistic pathways through which acute and chronic exposure to air pollutants can increase BP, including an imbalance in the autonomic nervous system, activation of the sympathetic nervous system, generation and release of proinflammatory mediators, and direct influence on the vascular endothelium,” said the study.