Q&A: Air pollution increases risk for AMD
Air pollution is a health hazard, and not only for the lungs.
The eyes, and particularly the delicate layers of the retina, may be affected, and chronic exposure may trigger or speed up the mechanisms that lead to age-related degenerative eye diseases.
A study published in the British Journal of Ophthalmology investigated the association between air pollution and AMD in a large sample of the U.K. population. Healio/OSN spoke with one of the authors, Tunde Peto, MD, MHealthEd, PhD, professor of clinical ophthalmology at Queen’s University Belfast, about the study.
Healio/OSN: What inspired your study?
Peto: Air pollution is one of the leading causes of death from non-communicable diseases and a phenomenon that is widespread both in high- and low/middle-income countries. Of particular concern are the levels of air pollutants to which predominantly women are exposed in the domestic environment due to the biomass smoke produced for cooking and heating in some countries. People also live longer, and it is therefore important to look at how the environment influences diseases that come with longevity. We have known for some time that smoking is a risk factor for AMD. However, fewer people smoke nowadays, particularly in the high-income countries, and while the rate of visual loss due to AMD is decreasing, due to the number of people aging, the absolute numbers are still increasing. Hence, the importance to investigate other risk factors, and air pollution is one of them.
Healio/OSN: What are the mechanisms through which air pollution may contribute to AMD?
Peto: The most likely mechanisms involve oxidative stress and inflammation. Oxidative damage to the retinal pigment epithelium (RPE) is an early event in AMD. The sick RPE cannot perform its function of cleaning the retina and providing nutrition and oxygenation to the outer segments of the photoreceptor cells. This contributes to RPE cell death and photoreceptor death.
Healio/OSN: Your study included 115,954 UK Biobank participants. Could you tell us more about the UK Biobank and the cohort that you included in your study?
Peto: The UK Biobank is a major study containing genetic and health information of 500,000 U.K. participants and is accessible to approved researchers. Volunteers who join the UK Biobank give their consent to linkage analysis to the hospital admission database, hospital procedures, and death and cancer registries. They sign in for a long-term commitment, and this is an advantage because we have long follow-ups and can relate diseases that occur later in life with baseline data. It is important to note that UK Biobank participants may not be a representative sample of the population because those who volunteer seem to be healthier than the general population and also more socially minded than the society as a whole. They may become actively engaged in follow-up cohorts, research projects, studies and surveys. In our study, we included 115,954 participants with self-reported AMD for which we were able to collect complete data on age, sex, race, BMI, Townsend deprivation index, smoking status, refractive error and air pollution measures related to the area where they lived. We also had complete OCT imaging data for about 69,000 participants.
Healio/OSN: How did you collect data on air pollution for these patients?
Peto: The air pollution estimates were provided by the Small Area Health Statistics Unit, a joint project of Imperial College London and King’s College London that aims at assessing the impact of environmental factors on the health of the population. This is also part of an EU consortium, the BioSHaRE-EU, that catalogs, secures and shares these data for various studies. From there, we were able to access the data on air pollution in different areas in the U.K. We were able to gather additional information from a U.K. geographic information system that analyzes special locations and integrates many different kinds of data such as traffic, land use for agriculture, industry, mixed use, residential only and other aspects that could help us determine the amount of air pollution to which each participant was exposed.
Healio/OSN: What were your findings?
Peto: We know that cigarette smoking is a risk factor for AMD, but our results showed that air pollution is independently related to AMD risk as well. Patients who were exposed to higher particle matter had an 8% higher risk for having self-reported AMD. This was also correlated with changes in the retinal structure, including thickness of photoreceptor and RPE layers on OCT imaging. This 8% increase may not sound like a lot, but if you think of the millions of pounds and dollars that are spent to treat AMD, 8% is a huge increase in terms of expenses and resources. And this is for just one disease that people may develop as a consequence of air pollution. Young people are exposed to these harmful particles, and the consequences may not show immediately. But later in life they may develop AMD, and because we live longer, the burden on our health care systems is becoming huge. It is important to be aware that not only the lungs are endangered by not having access to clean air. Our findings add to the growing evidence of the damaging effects of ambient air pollution and hopefully will contribute to raise awareness that air pollution is an important modifiable risk factor for AMD.
For more information:
Tunde Peto, MD, MHealthEd, PhD, can be reached at Queen’s University Belfast, University Rd, Belfast BT7 1NN; email: email@example.com.