As I write this column, my gaze is on the post-Deepavali haze that has enveloped Delhi. As a third-generation asthmatic, with a fourth-generation asthmatic daughter, it is set me wondering whether returning to Delhi, the city of my birth, from the United States a decade ago was a mistake. This haze is smog (smoke + fog), a hazardous mix of noxious gases and very high levels of suspended respirable particulate matter (PM). PM come in various sizes that can reach deep inside the lungs. The sources are many — automotive engines, firecrackers, waste burning, or even just dust from construction — but the end results are similar. A typical adult breathes about 10,000 litres of air per day, so even small quantities of PM2.5 (less than 2.5 micrometres in diameter) accumulate in the lungs, leading to oxidative damage and inflammation. While air quality measurements also include noxious gases and coarse particulate matter, e.g. PM10, PM2.5 forms the bulk of the Air Quality Index (AQI); higher values being worse. A glance at the AQI values for Delhi confirmed my suspicion that we were about to break previous records. With more than 100 being unhealthy, we were headed towards 1000!
Effects on healthSo how large is the risk and are such levels of pollution unseen previously? Looking back, pollution levels as high or higher than they are today seem to have existed in the coal-burning phase of Industrialisation. During the great London smog of 1952, which led to the British Clean Air Act of 1956, it was difficult to see during the day. Thousands of additional deaths occurred during the few weeks when the smog was at its worst. The most susceptible were the patients with chronic lung diseases, such as COPD and the death rates for such patients increased by more than two-fold for many months thereafter. This is not surprising because High levels of PM compromise the immune defence system of the lungs, predisposing to life-threatening infections such as pneumonias; especially those at the extremes age and people with respiratory disease. Patients with cardiovascular disease are also susceptible. Exposure to current pollution levels can increase blood pressure by as much as 20 to 30 mm Hg. Strokes and heart attacks would be a natural consequence. Even healthy people are affected, with increased risk of hypertension, asthma, Chronic Obstructive Pulmonary Disease (COPD), diabetes and heart disease.
Children growing up in areas with higher air pollution have an increased risk of asthma and reduced lung growth, comparable to maternal smoking, as seen in the Children’s Health Study from California. Not surprisingly then, Indians have the smallest lungs in the world, even when compared to westerners of similar height, weight, and socio-economic status. Given a natural decline in lung function that starts by the late twenties, those with smaller lungs seem to be at higher risk of developing disabling lung diseases like COPD earlier in life. This would be true even if they were able to reduce pollution exposure later in life, since lost lung function cannot be restored. Perhaps, this is one of the reasons (indoor smoke pollution being another) why we see a substantial burden of COPD in non-smokers; unusual in the West. The recent Global Burden of Disease (GBD) report on risk factors for health found air pollution to be the most important single risk factor for premature disability and death in India (see www.healthdata.org/india), accounting for 10 per cent of years lost due to ill-health, disability or early death (DALY). Tobacco smoke exposure accounted for just about half this risk. This should not, however, be misconstrued as a justification for smoking since this simply reflects the fewer number of smokers, who are individually at higher risk. Air pollution is not the only challenge though; dietary risks and maternal and child malnutrition have greater cumulative effects than air pollution, perhaps even on lung growth. The two may even interact, since a lack of dietary antioxidants increases the susceptibility to air pollution.
Harnessing technologySo what can be done beyond some obvious restraint while celebrating Deepavali? Reducing unnecessary vehicle use and encouraging public transport is important, as is switching to clean energy and not burning waste. It is less clear how we should mitigate the current threat. While indoor air purifiers can bring PM levels to safe ranges in closed parts of our homes, persisting outdoor exposure would remain. The few studies on use of indoor air purifiers have not shown to have unequivocal health benefit, although there were modest trends towards improved lung function and reduced inflammatory markers in blood. This may be because of continued outdoor exposure, which is harder to protect against. Ordinary masks do not provide much protection and N-95 respirators are cumbersome. Nasal filters look promising but need more testing. A complementary strategy is antioxidant supplementation to limit the pollution-linked oxidative damage. Vitamin C has shown some beneficial effects in small human studies and newer mitochondria-targeted antioxidants may be better. There is also a natural experiment going on — where different people are responding differently to similarly threatening levels of pollution; some susceptible, some resistant. An understanding of these differences could be translated into effective ways to reduce susceptibility. Research into such areas is sorely needed and we, at the Council of Scientific & Industrial Research (CSIR), have identified this as a priority area where science and technology can make a difference to human lives.
At the end, I would like to re-emphasise that the benefits of improving air quality are likely to be substantial. The landmark Six Cities study in the U.S. showed that people living in clean air cities lived two to three years longer, on average, than those living in dirty air cities. Importantly, the air quality of their dirty air cities was much better than here; well within the safe range. Further improvements in air quality added another year to life expectancy, even in the so-called clean air cities. My ‘guesstimate’ is that Indians stand to gain at least five to ten years of healthy life by taking decisive action to improve the air we breathe. Continued apathy and inaction would mean a life less lived, for our children, and us. That would certainly be a mistake!
Anurag Agrawal is a pulmonary physician and principal scientist at the CSIR Institute of Genomics and Integrative Biology, Delhi. He heads the CSIR Centre of Excellence for Translational Research in Asthma and Lung disease.
