Long-term exposure to severe air pollution increases mortality, but whether long-term exposure to levels below established limits also impacts health is unknown.
In a recent publication in the Lancet, a large consortium grouping 22 European cohorts aimed at assessing the effects of long-term exposure to air pollution. The authors followed more than 350,000 participants for an average of almost 14 years, and collected more than 29’000 deaths from natural causes (violent deaths such as suicides were excluded). A considerable effort was undertaken to standardise all the data collected and to take into account average air pollution, the participant’s address and its vicinity to road traffic. The analysis was performed taking into account participants characteristics that might have blurred the association between air pollution and mortality, such as smoking, presence of disease, healthy eating, obesity, education... Among all air pollutants studied, the authors found that an increase of 5 micrograms per cubic meter of air of particulate matter (PM) with diameters of less than 2.5 micrometers (one thousandth of millimetre – PM2.5) increased mortality by 7%. This increase was observed irrespective of the country and, most importantly, this increase was found even in the Nordic countries, where pollution levels were the lowest. Apparently, no increase was found regarding mortality due to cardiovascular diseases, but more information will follow.
PM2.5 comes mainly from combustion activities such as motor engines, power plants and domestic activities such as wood or charcoal burning. Depending on the country, the main source of PM2.5 might differ, making global recommendations difficult.
Still, this study shows that there is no “safe” limit for air pollutants and that tight control of air pollution levels is advisable for the benefit of both environmental and human health.