Polluted air linked to increase in blood pressure: Study
A seven-year study until 2016 involving 5,300 adult residents of different parts of Delhi found that exposure to polluted air was linked to an increase in systolic and diastolic blood pressure (BP) and an enhanced risk of developing hypertension.
Out of the randomly selected participants, 3,000 developed hypertension during the study period while the rest were already hypertensive.
The study published in the AHA journal of Hypertension on August 17 found higher average systolic BP with higher PM 2.5 exposure. For every 15 micrograms per cubic metres exposure in PM 2.5, there was an increase in 3.3 mm Hg in systolic BP. Average annual PM2.5 exposure (ranging from 87 to 138 micrograms per cubic metres) over 1 year, 1.5 years and 2 years increased the risk of developing hypertension by 50%, 60% and 20% higher, respectively. The risk for exposure of two years was found to be lower because those who were likely to develop hypertension developed it during the 1 to 1.5-year period.
These results were also found to be stronger in study participants with higher waist-to-hip ratios, which are an indicator of obesity.
The authors of the study from Harvard TH Chan School of Public Health, Public Health Foundation of India (PHFI) and Centre for Chronic Disease Control, India, collected questionnaires and annual year blood pressure measurements and developed a high-resolution model to assess their exposure to air pollution.
The model was fed with PM 2.5 data from the Central Pollution Control Board, Delhi Pollution Control Committee, satellite data, etc, to study how PM 2.5 exposure affected blood pressure over time.
The heightened effect of PM 2.5 exposure observed in this study may not be simply due to the higher exposure but also the composition of PM2.5 in Delhi, authors have noted. The major sources of PM2.5 in Delhi are traffic, power plants, industries, and regional sources of pollution such as agricultural crop burning which include metals, inorganic aerosol, carbon etc.
“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 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 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 (eg obese individuals). The results suggest there are significant benefits of controlling air pollution in reducing a major risk factor for cardiovascular deaths, the leading contributor to deaths in our country,” Dorairaj Prabhakaran, vice president, Research and Policy, PHFI, and the lead Investigator of the study said in a statement on Friday.
The study has concluded that “reducing exposure to ambient air pollution has a large impact in controlling blood pressure, reducing risk of developing hypertension and future cardiovascular disease, and ensuring overall well-being”. “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.”
“The association between air pollution and hypertension and other cardiovascular diseases is not new. The Harvard School of Public Health’s six-city study had already found that PM 2.5 exposure was linked to higher mortality. In northern Italy, which is highly polluted, Covid-19 mortality was 12% compared to southern Italy where it was 4.5 %. This also shows that air pollution can lead to higher mortality from Covid-19 indirectly. The treatment outcomes of Covid-19 in patients with hypertension are poor,” said Dr GC Khilnani, who heads pulmonary medicine department at New Delhi’s All Indian Institute of Medical Sciences.