In a response to a question raised in Parliament, the Ministry of Environment, Forests and Climate Change stated on January 4 that “there is no conclusive data available in the country to establish direct correlation of death/disease exclusively to air pollution”. It notes, however that air pollution may be a “triggering factor” for respiratory ailments. In an interview from 2017, the minister also stated that “no death certificate has a cause of death as pollution”.
These responses follow a pattern of reflexive defensiveness from the ministry towards dozens of studies published in the last few years linking rising air pollution levels to mortality and morbidity across the country. It also reveals a misunderstanding of the science backing these claims.
The detrimental effects of air pollution in India have been well known for decades with renowned cardiologist Dr S Padmavati publishing the first such study in 1959. She documented 127 cases of Cor Pulmonale, a cardio-respiratory condition, establishing a strong correlation with cooking smoke exposure.
Household and ambient air pollution have since been linked with heart attacks, asthma, lung cancer, chronic obstructive pulmonary disease, respiratory infections in children, prematurity and low birth weight, cataracts, and strokes. The reams of historical evidence in India on health effects have been documented exhaustively in the Ministry of Health and Family Welfare’s report on air pollution released in 2016, and more recent burden of disease estimates were released by the Indian Council of Medical Research and the Public Health Foundation of India in December 2018.
Causal links
All diseases, including those listed above, are by their very nature multifactorial, with individual and environmental factors – such as air pollution – explaining their occurrence. But this cannot by itself counteract the claim that there is a causal link between air pollution and these diseases. The causal pathways for air pollution-induced diseases have been established through clinical, epidemiological and quasi-experimental studies in laboratories, communities and large populations, through controlled exposure studies on humans and animals, and across developed and developing countries representing a wide spectrum of exposures.
Epidemiology, by its very nature, seeks to explain the determinants and patterns of disease occurrence at a population level. Epidemiological studies can estimate the causal contribution of a particular risk factor to a disease by estimating the attributable fraction. This should serve as the basis for designing policy interventions for primordial and primary prevention of disease.
The burden of disease study does this, and reveals that the fraction of lung cancer attributable to environmental factors is about 33%, and that of lower respiratory infections is about 43%. The causal evidence for air pollution as a factor for disease incidence is therefore sound, and indeed alarming.
The best evidence
In the absence of unethical and impractical randomised trials to establish a “direct correlations” between air pollution and disease, this is and will be the best evidence we have to work with, as evident from its use by environmental authorities across the developed and developing world. On a practical note, air pollution cannot also be listed as a cause of death on a death certificate since there is no code in the International Classification of Diseases, which appear on medical billing and death certificates and are used to identify trends in diseases over time, for air pollution. Neither is there one for smoking, for that matter.
The mid-20th century witnessed a similar debate around the harmful effects of smoking and its link with lung cancer. Epidemiological studies had revealed a strong causal association between smoking and lung cancer, but skeptics pushed back, suggesting that population-level estimates cannot be considered causal and extrapolated to individuals. Several decades on, the debate on smoking and lung cancer has long concluded, but the rhetoric around air pollution seems to be treading a similar unfortunate path.
There will always be scope for better, more robust local studies to buttress the evidence base, but it is hard to see how Indian lungs could respond to air pollution any differently than those of our American, Chinese or European counterparts. In the face of overwhelming global evidence, it is imperative that initiatives such as the National Clean Air Programme be operationalised immediately with time bound targets for significant reductions in air pollution, in line with India’s Sustainable Development Goal commitment to substantially reduce the number of deaths and illnesses from pollution. India would also do well to engage physicians and epidemiologists in addition to environmental scientists in policymaking on air pollution, as is practice elsewhere, to better inform an often perplexing public discourse.
The writer is a doctor of public health candidate at the Harvard TH Chan School of Public Health and co-Founder of Care for Air.