Home to nearly 1.4 billion people (World Bank 2022), India is one of the most populated countries in the world. India also has some of the highest levels of air pollution, with an estimated population-weighted mean fine ambient particulate matter [PM [less than or equal to]2.5 [micro]m in aerodynamic diameter (PM25)] concentration of 91.7 [micro]g/[m.sup.3] in 2019 and virtually all people living at levels above the World Health Organization's (WHO) Air Quality Guidelines (India State-Level Disease Burden Initiative Air Pollution Collaborators 2021). Given these high exposures, it has been estimated that nearly 1 million deaths and 31 million years of healthy life were lost in 2019 due to ambient [PM.sub.2.5].
These burden estimates clearly suggest a public health problem requiring intervention. However, these estimates (and other global and regional estimates) rely on evidence generated from elsewhere in the world--largely in North America and Europe, and only more recently from Asia and the Middle East. Although experts have argued that relying on estimates from other nations should produce reliable estimates for India in the absence of area-specific information (GBD MAPS Working Group 2018; Ministry of Health and Family Welfare, Government of India 2015), why has local evidence not been available? The answer lies with a historic lack of data in India. Reporting by the Civil Registration System Division in India indicates steady improvement in the capture of deaths by administrative records over time but the data completeness did not exceed 70% until after 2018 (ORGI 2020). For many states and region territories, the capture is closer to 50% and, nationally, <20% of deaths are medically certified with an underlying cause. In addition, local and national air pollution data and modeled estimates have only become widely available in the last 5-10 y.
Brown et al. (2022) address this knowledge gap by leveraging data from the Million Death Study and satellite-derived estimates of ambient PM25 concentrations for India. Specifically, they linked ambient PM25 (0.1[degrees] resolution) to cause-specific mortality rates for nearly 7,500 urban postal codes and rural villages throughout India. In these communities, nearly 7 million individuals were actively surveilled for mortality using a validated instrument. For every 10-ig/[m.sup.3] increase in estimated PM25, they documented a 9% higher rate for stroke mortality (95% confidence interval: 1.04, 1.14) after adjustments for age, sex, time, area-level urbanicity, area-level socioeconomic characteristics, and place. More modest associations were observed with non-accidental and chronic respiratory disease mortality, and null associations were found with heart attack mortality. Notably, given the interquartile range in India (~ 20 ig/[m.sup.3]), these associations appear even larger (up to 1.17) when expressed as contrasts between high- and low-exposed individuals.
Overall, these findings confirm that air pollution likely results in premature mortality in India, mostly via stroke. Many of the associations, however, were weaker than what may have been expected given the current global evidence on the association between air pollution and respiratory and cardiovascular diseases. This may be important because burden estimates, including those by the Global Burden of Disease project and WHO assume...