Long term exposure to air pollution linked with 1.5 million deaths annually in India: Lancet Study

Long term exposure to fine particulate matter (PM2.5) pollution levels higher than the WHO guidelines is potentially associated with 1.5 million deaths a year in India, shows a study published in the Lancet Planetary Health journal.

According to the findings by the Consortium for Climate, Health and Air pollution Research in India (CHAIR-India), the 1.4 billion people in India live in areas with PM2.5 concentrations above the recommended 5 micrograms per cubic metre (μg/m³) annual average recommended by the WHO. 

This is the first Indian study to use difference-in-difference method, a causal methodology to isolate the effect of long-term PM2.5 exposure (annual) and all-cause mortality. 

The study observed that the risk is high even at lower air pollution levels, indicating the need to reduce air pollution levels across the country. It included annual death data reported across all districts and PM2.5 exposure from a spatio-temporal model built for India. 

Major findings: 

1. Every 10 μg/m3 increase in annual PM2.5 exposure is associated with an 8.6% increased risk for mortality across India.
2. Unlike previous studies, this study used PM2.5 exposure from a fine spatio-temporal model built for India and annual mortality counts reported across all districts of India.
3. First Indian study to use difference-in-difference method, a causal methodology to isolate the effect of long-term PM2.5 exposure (annual) and all-cause mortality.
4. During the study period (2009 to 2019), 25% of all deaths (~1.5 million deaths a year) were attributed to annual PM2.5 exposure higher than the WHO guideline value of 5 μg/m3 across the country.
5. About 0.3 million annual deaths are attributed to annual exposure to PM2.5 above the Indian National Ambient Air Quality Standards (NAAQS).
6. The exposure-response function revealed higher incremental risk for mortality at lower PM2.5 concentrations and levelling off at higher PM2.5 concentrations.

 The evidence supporting the association between long-term exposure to outdoor air pollution and deaths in India is scarce and inconsistent with studies in other countries. 

The authors of this study thoroughly analysed the annual deaths from 2009 to 2019 at a district level in India and obtained annual PM2.5 concentrations by a machine learning based model using satellite data as well as ground-monitoring observations of air pollution levels across 1056 locations.

The results of the study highlight the extent of the mortality burden due to PM2.5 pollution in India, the world’s most highly populated country, and underpin the need for stricter air pollution guidelines to prevent the excess mortality due to air pollution.

Implementing stronger air pollution guidelines is crucial to reducing this excess mortality and protecting the health of millions of people across the country.

CHAIR-India consortium comprises of leading Indian academic institutions such as the Centre for Health Analytics Research and Trends (CHART) at Ashoka University, the Centre for Chronic Disease Control (CCDC) and global institutions like Karolinska Institutet (Stockholm, Sweden), Harvard University, Boston University, and the Icahn School of Medicine at Mount Sinai (USA), Ben-Gurion University of the Negev (Israel), and the Department of Epidemiology, Lazio Region Health Service/ASL Roma 1 (Italy). 

 Insights from Researchers:  

Researchers emphasize the necessity of a comprehensive and systematic approach to addressing air pollution.  “High levels of annual PM2.5 exposures are observed in India causing a huge mortality burden (not limited to cities that are highlighted during the extreme pollution episodes), signaling the need for systematic and not symptomatic approach,“ Suganthi Jaganathan, doctoral researcher, Centre for Health Analytics Research and Trends (CHART), Ashoka University, CCDC and Karolinska Institutet said.

Commenting on the study, Poornima Prabhakaran, Director - CHART, Ashoka University and Deputy Director & Head - Environmental Health, Senior Research Scientist at the CCDC and principal investigator from India for the CHAIR-India consortium said, “This study used a new analytical approach to demonstrate the mortality associated with exposure to high annual levels of PM 2.5 beyond the recommended WHO levels. This signals yet again the need to mount stringent air quality management strategies across India.”  

“Delhi may get the headlines, but this is a problem all over India, and nationwide efforts are needed. Coal burning electric plants need scrubbers, crop burning needs to be limited, and most importantly, we need urgent measures to protect population health.” said Joel Schwartz, Professor, Harvard T.H. Chan School of Public Health and principal investigator from the US for the CHAIR-India consortium. 

Highlighting the importance of the study, Petter Ljungman, Associate Professor at the Karolinska Institutet and principal investigator from Sweden for the CHAIR-India consortium said, “This nation-wide analysis of air pollution mortality using data from India brings important evidence to policy makers of the striking health impact of ambient air pollution all over the country. The fact that a significant level of mortality was evident for PM2.5 levels far below the current Indian standards is alarming.

"The range of PM2.5 pollution exposure was quite large across the years, with the lowest annual PM2.5 concentration of 11.2 μg/m³ observed in Lower Subansiri district, Arunachal Pradesh, in 2019 and the largest annual PM2.5 of 119.0 μg/m³ observed in Ghaziabad, Uttar Pradesh, and Delhi in 2016. The model estimated an increase in annual all-cause death rates by 8·6% (6·4–10·8) per 10 μg/m³ in annual PM2.5 exposure," Ljungman said.

Limitations:

The authors further highlighted some limitations of the study, including that - as with all models - there will be some uncertainty in the estimates, but say their results indicate previous estimates of deaths linked to chronic PM2.5 pollution exposure in India are considerably underestimated, stressing the need to progress rapidly and comprehensively towards reducing the levels of air pollution across India.