Results chime with earlier review indicating almost every cell in the body may be affected by dirty air
The number of health problems linked to air pollution could be far higher than previously thought, according to research suggesting hospital admissions for conditions ranging from heart failure to urinary tract infections increase as air becomes dirtier.
Air pollution has already been associated with a number of conditions, from strokes to brain cancer, miscarriage and mental health problems.
However, the research suggests the impact could be far wider, despite looking at only one component of air pollution, chiming with a global review published earlier this year that indicated almost every cell in the body may be affected by dirty air.
“The drive behind [the new research] was to do the most comprehensive study ever conducted at looking at all possible causes of hospitalisation that could be [linked] to exposure to fine particulate matter,” said Prof Francesca Dominici, of Harvard University and co-author of the study.
Writing in the BMJ, Dominici and colleagues report how they analysed more than 95m insurance claims made between 2000 and 2012 by hospital inpatients in the US aged 65 or older enrolled in the Medicare programme.
They then looked at air pollution, focusing on levels of a type of fine particulate matter, known as PM2.5, which is produced by sources including vehicles and power stations. By harnessing air quality data from a range of sources, they were able to estimate PM2.5 levels for each patient based on their home zip code.
The team then compared air pollution levels for each patient during the two days around their hospital visit with levels from other points in time.
This approach essentially takes into account factors such as age, socioeconomic status and even obesity, since it uses each patient as their own reference. Fluctuations in air temperature and other factors were taken into account separately.
The results back up previous studies showing a link between short-term exposure to dirty air and conditions such as heart failure, pneumonia and heart attack.
Indeed, the analysis suggests even a small average rise in PM2.5 of 1 micrograms per cubic metre over a two-day period is linked to an increase of 68 older people per billion being taken to hospital with heart failure the next day.
Put another way, that increase in air pollution raises the risk of such people being hospitalised with heart failure by 0.14% .
However, the team also found diseases including septicaemia, Parkinson’s disease and urinary tract infections were associated with poorer air quality. For the latter, the team estimate the short-term rise in PM2.5 is linked to a further 39 older people per billion being taken to hospital the next day.
While the increases in risk might look small, the team say a 1 micrograms per cubic metre rise in PM2.5 levels occurred on more than 122 days in each year within each zip code.
The team’s analysis further reveals air pollution is linked to more than just hospital visits: the data shows short-term increases in PM2.5 were linked to an average annual increase of 634 deaths, and about $100m in costs for inpatients and post-acute care.
Even when the team looked at days when the air quality was within the limits set by the WHO, they found the trends remained.
Yaguang Wei, first author of the study, said the research suggested the health effects of PM2.5 were not restricted within individual organs. “It has a more systemic effect on multiple pathophysiological processes such as inflammation, infection, and water electrolyte balance,” he said, although the details remain unclear.
While the study cannot prove that air pollution causes the diseases, the team say it adds weight to calls for air pollution guidelines to be reviewed.
Dr Ioannis Bakolis, of King’s College London, who was not involved in the study, agreed. He said: “These guidelines needs to be revised, as even the 9% of the population that lives within the WHO limits may be substantially by affected by air pollution concentrations and its associated costs, according to the findings of the study.”
However, the study has limitations, including that it looked only at one component of air pollution and only considered outdoor air pollution near patients’ homes.
What’s more, it does not account for short-term changes in behaviour that might have varied with air pollution levels – such as physical activity levels – while it is not clear if the results would hold in those not enrolled in Medicare, including younger people.
Writing in an accompanying editorial, a team of experts from the University of Southampton say the study suggests figures for the number of early deaths down to air pollution – put at 800,000 a year in Europe – are likely to be considerable underestimates, and stressed action is needed.
‘Clearly, there is much still to learn, but we should not mistake knowledge gaps for paucity of evidence,’ they write. ‘The sooner we act, the sooner the world’s population will reap the benefits.’