Overview of the Indian National Burden of Disease from
Indoor Air Pollution

Kirk R. Smith
University of California, Berkeley, and East-West Center, Honolulu
 
Table 1. Estimate of Annual Pre-Mature Mortality from Air Pollution for World and India.
Table 2. Indian National Burden of Disease:
Tables 3 and 4 are unavaliable here.

 Air pollution has become a major concern in India in recent years both because it is now clear that large parts of the Indian population are exposed to some of the highest pollutant levels in the world and also because new studies around the world on the health effects of particulate air pollution have increased confidence in estimates of the risks posed by air pollution exposures.   As in other parts to the world, air pollution is most obvious outdoors in Indian cities, where transport, industry, household, and other sources combine to produce excessive levels in many cases.  Recent estimates of the pre-mature deaths each year from outdoor air pollution in Indian cities have ranged from 50-200 thousand.  See Table 1 for a comparison of recent estimates of air pollution mortality worldwide and in India.

Unlike developed countries, however, poor countries such as India, have another,  somewhat hidden, source of air pollution that produces high levels of human exposure.  This is the use of solid fuels, mainly coal and biomass such as wood, crop residues, and dung, as household fuels in simple stoves.  Studies have shown that household stoves, although individually small and having a smaller influence on outdoor levels than industrial and transport sources, actually create larger human exposures to many important air pollutants.

In general, the percent of pollution emitted that actually is breathed in by somebody (the “dose effectiveness”) is much higher for indoor sources than outdoor sources, sometimes hundreds of times, simply because people are nearby and pollutants are poorly dissipated.  In addition, unprocessed solid fuels, such as biomass and coal, have tens of times higher emission factors (pollutants released per unit fuel) in simple cooking devices than even the crudest liquid and gaseous fuels.  This, then, is unfortunately the prescription for large human exposures, i.e., a frequent highly polluting process (cooking with solid fuels in simple stoves) done in times and places with many people and relatively little dispersion of pollutants (households).

Health effects, of course, are commensurate with exposures.  As shown in Table 1, recent estimates of the premature deaths in India from such indoor exposures range from 500 thousand to two million (5 -20 lakh) per year.

Problems with the Top-Down Approach

Unfortunately, however, these previous estimates of pre-mature deaths from air pollution in India have had to primarily rely on health effects studies of urban outdoor particulate air pollution in developed countries where conditions are substantially different from those in India, particularly in the rural indoor situations where most exposures occur.  This “top-down’ approach to estimating overall mortality raises several questions in the Indian context.   Principal among these are:

--Differences in pollutant mix due to different sources, i.e. although particulates can be used as indicator of hazard in both cases, biomass fuels produce relatively more organic compounds and fossil fuels more sulfur oxides.  Thus risk (dose-response) estimates derived in the latter situation may not apply to the former.

--Differences in exposure patterns, i.e., indoor concentrations tend to vary much more during the day (because of household cooking and heating schedules) than do outdoor urban levels.

--Different exposure levels, i.e., the average exposure levels of concern in households using unvented biomass fuels are 10-50 times greater than the levels studied in most recent urban outdoor studies. As has been shown with cigarette smoking, there is likely to be a diminishing of the effect per unit increase in exposure at these high levels.

--Different populations, i.e., the pattern of disease and competing risk factors differ dramatically between urban developed-country populations, the world’s richest and most healthy populations, and people exposed to indoor air pollution in developing countries who tend to be the poorest and most stressed populations in the world.

Given these concerns, estimating ill-health using the “top-down” approach is a rather crude and uncertain way of predicting the impact of air pollution for the exposures of interest.  It has been used, however, since there have not been studies funded among these populations.  Given the apparent high total exposure to these populations, it has seemed well justified to apply the best available risk information, even if far from ideal.
 

Bottom-Up Method

Although no large-scale mortality studies of indoor air pollution have apparently yet been done in India allowing use of such top-down methods for indoor exposures, over the last decade or so a number of studies of individual diseases have been done in India and other developing countries.  Although not in the quantity or sophistication that are warranted by the size and exposure of the population involved, their number and consistency are sufficient to enable their use as for estimating overall health impacts.

This allows the use of a “bottom-up” approach, which starts from the actual disease pattern in India and attempts to determine the proportion due to indoor exposure for the particular diseases known to be related to air pollution and for which specific studies have been done.  The risks due to air pollution of each of the diseases known to be important in India are evaluated one by one using studies from developing-country households using solid fuel.  Both mortality and morbidity estimates can be derived in this fashion.  Although information is not available for all of them, those for which impacts can be determined, when summed, represent another estimate of national impacts.

Comparison between the results of the two methods (top-down and bottom-up) will help in making a final range of estimates.   The following summarizes what has been done in such an effort undertaken as part of IGIDR’s contribution to UNDP’s Capacity 21 Project in India (Smith, 1998):

1. The air pollution that matters for health is what actually reaches people’s lungs, which is termed exposure.

2. In India, the largest particulate exposures are experienced indoors and in the neighbourhoods of the 80% of Indian homes where people cook/heat with solid fuels (dung, crop residues, wood, coal).

3. About 2 dozen monitoring studies have documented extremely high exposures in Indian homes under these circumstances.

4. There are two basic approaches to estimating health effects from these exposures:

--Top-down: apply results of the many studies done in developed-country cities on overall mortality from particulate air pollution;

--Bottom-up: sum the results of studies done in solid-fuel using households of developing countries for individual diseases of importance in India.
 
5. The following assumptions were used in this study to estimate total ill-health using both approaches, which use indoor particulate levels as the indicator pollutant:

--Distribution of solid-fuel use, population, and household size as in 1991 Census.

--25% of Indian households are assumed to cook outdoors with no air pollution exposure.

--10% of Indian households are assumed to have perfectly functioning smokeless chulas with no air pollution exposure.

6. Additional assumptions in top-down approach:

--High-end of indoor exposure range assigned to measured levels in Garhwal hill-region of Himalayas,

--measured distribution in urban areas applied to determine exposures in rural areas,

--baseline below which no effects are assumed to occur taken as Indian standards,

--low end of range of dose-response functions taken from WHO “meta-analyses” of US and European daily mortality studies,

--high end of range taken from WHO analyses of long-term mortality studies.

7.  The bottom-up approach first identifies the specific diseases associated with indoor exposures to biomass smoke in developing countries:

Shown in Table 2 is the national burden of disease (NBD) in India in the form of a list of those disease categories causing at least 1% of the NBD or at least 1% of all deaths.  Here the NBD is shown in as premature deaths and lost disability-adjusted life years (DALYs), as is becoming common in international comparisons.   This basically indicates the amount of healthy life expectancy lost  because of a disease, including both mortality and morbidity.  Note that the first four categories mostly (87%) affect children under five years, who as a result bear the largest overall ill-health burden of any age group.

As compared to the other seven major world regions, India bears the second largest burden of total ill-health on a per-capita basis.  The average Indian loses about 124 days of healthy life per year, second only to sub-Saharan Africa, which loses about 211 days per capita per year.   The main causes of disease are similar for these two regions, with some exceptions.  TB is relatively more important in India, for example, and malaria is more important in sub-Saharan Africa.  In addition to the total burden per capita, the proportion of ill-health due to environmental factors generally seems to decrease with economic development.

Air-Pollution Related Diseases

One of the major diseases thought to be associated with indoor air quality is Acute Respiratory Infections (ARI), a class that includes infections from a wide range of viruses and bacteria, but with similar symptoms and risk factors.  In every country, young children contract these diseases at similar rates, but in India and other poor countries they often proceed to severe stages, including pneumonia and death.

As shown in Table 2,  ARI is the largest single disease category for India, accounting for about one-eighth of the national burden.  For the world as a whole, ARI is also the largest category, accounting for about 8.5% of the global burden.  Astonishingly, Indian ARI is actually the largest single disease category in the world, in the sense of being subject to attention by one government. The Indian portion of this one disease class, which affects mainly one age group, accounts for 2.5% of the entire global burden of ill-health.

In Table 2, ARI and the other diseases thought to be associated with air pollution in studies around the world are marked with an asterisk.  Their scale alone, however, does not tell how much of each can be attributed to air pollution, because each has other important risk factors, including malnutrition and crowding.

Tobacco smoking exacerbates basically the same set of diseases and may overwhelm the impact of air pollution in active smokers.  In rural India, however, women probably receive the highest air pollution exposures due to their role as cook, but have low smoking rates.  Thus, here we focus on one of the major categories of ill-health in women thought to have air pollution as a risk factor: Chronic Obstructive Lung Disease (COLD), such as chronic bronchitis.  No attempt is made to calculate the burden on men, which is probably dominated by smoking.

Lung Cancer in women is a well-demonstrated outcome of cooking with open coal stoves in China (Smith & Liu, 1994).  There is little evidence of its connection to biomass fuel, however, and thus I account it here only to coal use in India.  Overall, being mainly non-smokers and non-coal users, Indian women have low lung cancer rates.

The relationship of indoor air pollution with the above three disease categories is relatively well established with evidence not only from outdoor air pollution, active smoking, and passive smoking studies, but also multiple studies in developing country households using solid fuels.

There are three other important disease categories in India for which there is some information about indoor air pollution as a risk factor: blindness, tuberculosis (TB), and perinatal effects.  In these cases, however, there are only 2 studies each actually done in developing country households.  India has a larger burden of blindness than any other major region of the world, accounting for 1% of its burden of ill-health as shown in Table 4.  Indeed, globally, one out of three cataracts occur in India where they are responsible for 80% of blindness in the country.

At nearly 5% of the total, India has a larger fraction of its national burden of disease due to TB than any other region, although the actual risk per person is less than in Sub-Saharan Africa.

Perinatal effects (stillbirth, low birthweight, death during the first two weeks after birth) are also a significant fraction of the total disease burden in India, as shown in Table 2.

The third category of diseases discussed here, cardiovascular diseases and asthma, are known to be related to outdoor air pollution in developed countries, but do not seem to have been studied in developing-country biomass-using households.  Heart disease rates among Indian women are not high by world standards, although still making up about 3.1% of the NBD for women.  Asthma rates are officially low (0.5% of NBD), although there is some recent evidence that the true prevalence is higher than previously thought.

8.  The bottom-up approach then reviews the available studies that quantify the impact of indoor air pollution on these diseases in developing country households.  The following risk factors were chosen according the strength of the available evidence:

Strong Evidence

Acute Respiratory Infections: “Meta-analysis” of 10 studies in developing countries resulted in an odds ratio of 2.5, thus a range of 2-3 taken (meaning that exposed children have 2-3 times more risk of serious ARI than unexposed children).  Only children under 5 years are considered.  See Table 3 for a description of the major studies as well as the bibliography by McCracken and Smith (1997) and the review by Samet et al. (1998).

Chronic Obstructive Lung Disease: “Meta-analysis” of 4 studies in developing countries resulted in odds ratio of 3.0, thus a range of 2-4 is taken.  Only the risk for women is considered.  See Table 4 for descriptions of major studies.

Lung Cancer from coal use:  Typical odds ratios in Chinese studies of 3-5 are used for women only.  The effects are apparently small under current Indian conditions, where relatively few households use coal .  (Smith and Liu, 1994).

Moderate Evidence

Blindness: The risk is assumed to be half of reported value for cataracts only, since only relationship to partial blindness has been found yet. Odds ratio (1.3) from Indian National Family Health Survey (NFHS) is used as high end of range; 50% of excess risk (1.15) used as low end.  A clinical Delhi study found similar risks.  Only the risk for women is determined.  No deaths are accounted to blindness.

TB: The odds ratio (3.0) from NFHS is used as the high end, 1.5 used as low end.  Mishra et al., 1998)   A study in Lucknow found a similar risk.  Only the risk for women is included.

Perinatal  Effects:  Although there are studies in Ahmedabad on stillbirth and in Guatemala on low birthweight, the difficulty of translating to health effects precluded including any risk in the total here.

Suggestive Evidence

Cardiovascular Disease and Asthma: Because of lack of developing-country studies, same approach taken as with “top-down” approach except that the dose-response curves were cut by 50% to account for high-dose effect.  Women only for heart disease.  Because the background rate for asthma itself in India is apparently small, there is little contribution from air pollution.
 
Results and Conclusion

The results of applying the two methods are as follows:

--Top-down: 360,000 - 1,800,000 premature deaths per year.  The wide range of uncertainty is due to the difficulty of applying the results of studies done in entirely different circumstances.

--Bottom-up: 410,000 - 790,000 premature deaths per year.

Chosen as the best estimated range: 410,000 - 570,000, with a best single estimate of 500,000 (5 lakh).  This takes the whole range for ARI, COLD, and lung cancer, but only the low end of the range for the rest.  Lung cancer, asthma, and blindness from this risk result in only a few hundred deaths.  The vast bulk are distributed roughly as follow: ARI-71%; CVD-12%, TB-12%, COLD-5%,  which reveals the dominance of ARI in the total.  On a lost life year basis, ARI is even more dominating with 86% of the total.

 It is important to note that these estimates only applies to children under 5 and women for the specific diseases listed above.  In reality, there are certainly also effects in other population groups and from other diseases.  The result is shown in bold lettering in Table 1 for comparison with studies done by the top-down method.

Although undoubtedly an advance over previous estimates, the results of this report still need to be considered tentative.  They should, however, be viewed as alarming indicators of the potential magnitude of particulate air pollution health effects in the country.    They emphasize the urgent need to more fully and directly investigate the health effects of air pollution in India itself so that extrapolations from other populations can be avoided.  They also demonstrate the need to embark on more research and demonstration of the many forms of intervention that could reduce the apparently great health burden that now is borne by some of the poorest and most vulnerable members of Indian society.

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Table 2. Indian National Burden of Disease:  Disease categories accounting for at least 1% of lost DALYs or 1% of deaths.  Also showing percent of burden in children under 5 and overall female/male ratio.  (Murray and Lopez, 1996)


ARI= Acute Respiratory Infections;  Child Cluster= Measles, Tetanus, Pertussis, Polio, Diphtheria; COLD= Chronic Obstructive Lung Disease; DALY= Disability-Adjusted Life Year;  STD= Sexually Transmitted Diseases;  Tropical Cluster= Schistosomiasis, etc.
*Not on the global list of 1% diseases.  On the global list, but not on India’s, are malaria, war, violence, alcohol (direct effects), and drowning.
a.  Children under 5 are 14% of  the national population.  b.  Ratio of DALYs lost at all ages.
c.  For total national burden.