GLOBALLY, outdoor air pollution was responsible for an estimated 3.7 million premature deaths in 2012.
Of these deaths, 80% were due to ischaemic heart disease and stroke, 14% were due to chronic obstructive pulmonary disease or acute lower respiratory infections, and 6% were due to lung cancer. In the European Union, where outdoor air pollution levels are generally low, it is estimated that air pollution has reduced average life expectancy by about 8.6 months.
The strongest epidemiological evidence for the adverse health impacts of air pollution is for effects on the cardiovascular system — for example, heart rate variability, development of atherosclerosis, myocardial ischaemia, myocardial infarction and premature deaths. Effects on the respiratory system include exacerbation of asthma and premature deaths.
A recent study published in the New England Journal of Medicine highlighted that improvements in outdoor air quality were significantly associated with improvements in lung function growth in children. In other words, the adverse effect of air pollution on lung growth in children is reversible.
The accompanying editorial made the salient observation that the reversibility of lung function growth has important ramifications as reduced lung function in childhood is a strong predictor of both chronic respiratory and chronic cardiovascular disease in adults.
Investigating and commenting on the effects of air pollution is no longer the domain of environmental epidemiologists alone.
The American Heart Association, after reviewing the evidence on air pollution and cardiovascular disease, concluded that the overall evidence is consistent with a causal relationship between air pollution exposure and cardiovascular morbidity and mortality. Both the American Lung Association and the American Thoracic Society prominently feature air pollution as a risk factor for respiratory disease on their websites.
Importantly, the American Heart Association has also deemed air pollution exposure a modifiable risk factor for cardiovascular morbidity and mortality. Outdoor air pollution should be viewed in the same manner as the more traditional modifiable risk factors for cardiovascular disease such as cigarette smoking and hypertension.
Australian cities have relatively low levels of air pollution compared to most other major cities in the world. Air quality in Australia has improved over the past few decades and rarely exceeds the national air quality standards. However, this should not be a cause for complacency.
It is accepted that there is no threshold level for the common air pollutants below which health effects do not occur. Further improvements in air quality, even if within the national standards, will have beneficial health effects for everyone.
If air pollution is a modifiable risk factor for respiratory and cardiovascular diseases, what advice can the medical profession give to patients when discussing ways of reducing their risk of these diseases?
The “Guidelines for the assessment and management of absolute cardiovascular disease risk” (National Vascular Disease Prevention Alliance, 2012) make no mention of air pollution as a risk factor. Although it is not possible to assess individual patient’s air pollution exposure, clinicians can advise their at-risk patients to reduce air pollution exposure, for example, by avoiding or restricting outdoor activities on high air pollution days.
The most effective approaches to reducing exposure to air pollution will continue to be population-based air pollution control strategies (such as legislation to control industrial and motor vehicle emissions) which reduce the exposure to air pollution for as many people as possiible.
There is also a role for the medical profession, both individually and organisationally, to advocate for cleaner air — you will be doing everyone a favour.
Professor Bin Jalaludin is conjoint professor at the School of Public Health and Community Medicine, University of NSW, and chief investigator, Centre for Air quality and health Research and evaluation (CAR).
The annual scientific meeting of the Australia and New Zealand Society of Respiratory Science and The Thoracic Society of Australia and New Zealand is currently under way in Queensland.