A major international study confirms that long-term exposure to air pollution does not solely increase the risk of lung cancer but also increases the risk of cancer in other organs.
Most people assume that air pollution increases the risk of developing lung cancer, but more and more studies suggest that it also increases the risk of developing other types of cancer, including breast, bladder and colon cancer.
A new and very extensive international study with participation from Denmark now shows that people living in areas with higher air pollution have a significantly increased risk of developing liver cancer.
Previous studies have found this association. However, although the air quality in Denmark is among the best in Europe, the fact that the association has now been established beyond doubt is a wake-up call that air pollution still harms health.
According to a researcher behind the study, air quality needs to be improved further.
“There is no escaping air pollution. You need to breathe, and we are therefore all exposed to some air pollution. However, this study shows that a small increase is sufficient to increase the risk of developing liver cancer,” explains a leader of the new study, Zorana Jovanovic Andersen, Professor with Special Responsibilities, Department of Public Health, University of Copenhagen.
The first author was Rina So, PhD student, Section of Environmental Health, Department of Public Health, University of Copenhagen.
The research results have been published in the International Journal of Cancer.
Data from six population cohorts in five European countries
The study, which is part of a large study ELAPSE (Effects of Low-Level Air Pollution: A Study in Europe), supported by the Health Effects Institute, has included data from population surveys in Denmark, Sweden, the Netherlands, France and Austria.
The data from Denmark are from the two population cohorts Diet, Cancer and Health, covering Copenhagen and Aarhus, and the Danish Nurse Cohort, covering all of Denmark – both containing health data for thousands of people.
Similarly, the other participating countries have obtained data from their population cohorts, following study participants for many years.
The researchers used the population cohorts to determine the incidence of liver cancer and linked this with where people had lived and their exposure to air pollution at their home address.
“We linked their health data to their address history. Then we used air pollution models based on the concentration data from the European Environment Agency AirBase to determine each person’s exposure to particulate matter and nitrogen dioxide. Six small studies have shown a possible association with liver cancer, but linking many registries from many countries clearly showed whether there is an association and how much the risk of developing liver cancer increases,” says Zorana Jovanovic Andersen.
Denmark is below EU particulate matter limit level but should be even lower
The researchers found that the risk of developing liver cancer increased by 12% for every 5 μg/m3 increase in air pollution from particles with an aerodynamic diameter of less than 2.5 μm (PM2.5).
This 5 μg/m3 corresponds to the difference between living on a major road, H.C. Andersens Boulevard in central Copenhagen, versus living on a side street. The annual average for PM2.5 on H.C. Andersens Boulevard is about 17 µg/m3.
“Since 2008, Denmark has complied with the European Union limit value for PM2.5 of less than 25 µg/m3, but even concentrations below this are associated with an increased risk of developing liver cancer. This indicates that air pollution needs to be reduced even further,” explains Zorana Jovanovic Andersen.
Many people probably die from liver cancer caused by air pollution
The researchers also investigated how the concentration of nitrogen dioxide in the air affects the risk of developing liver cancer.
For every 10 µg/m3 of extra nitrogen dioxide in the air, the risk of developing liver cancer increased by 17%.
Zorana Jovanovic Andersen says that this indicates that much work needs to be done to further reduce air pollution.
The number of people dying from liver cancer caused by air pollution in Denmark is still not known but is clearly substantial.
“Air pollution accounts for 20% of all deaths from lung cancer. This association is quite clear, as is the association for liver cancer. We also conclude that keeping air pollution below a certain threshold will not eliminate liver cancer,” says Zorana Jovanovic Andersen.
Major potential to improve public health
According to Zorana Jovanovic Andersen, the new study will contribute significantly to the negotiations in the European Union on what levels of air pollution are acceptable.
In this context, the study is not alone. Over the coming years, the same research group will also present results regarding associations between air pollution and the risk of bladder cancer, breast cancer, colon cancer and other types of cancer that have not previously been so strongly associated with air pollution.
Zorana Jovanovic Andersen says that the study has two important conclusions.
· The home address at which people are exposed to air pollution is clearly associated with the risk of developing liver cancer. This association already exists for concentrations below the current limit values.
· The study also indicates that researchers’ knowledge on how air pollution affects many diseases remains limited and inconclusive. Clear associations have been established between air pollution and lung cancer, respiratory and cardiovascular diseases and now also other types of cancer. But more associations will probably be discovered in the future, such as with dementia.
“When examining the risk of developing cancer, it is worth remembering that cancer is the leading cause of death in Denmark and has substantial societal cost. This provides a clear incentive to reduce air pollution further to save both lives and money. Reducing air pollution is effective in preventing many diseases that are very expensive for society,” concludes Zorana Jovanovic Andersen.
