The effects of pollution on human health are often subtle but pervasive. An exemplary new study on Tuesday appears to indicate that high exposure to certain car fumes can increase the risk of developing a degenerative disease that permanently erodes vision.
The disease is known as age-related macular degeneration or AMD. AMD is characterized by the progressive destruction of the macula, a part of the retina that allows us to look straight ahead with a clear and sharp focus. The progression of AMD can vary, with some people experiencing minor vision problems for many years, while others deteriorate rapidly. Although the disease does not cause complete blindness, it is generally one of the leading causes of irreversible vision loss in people over 50 years of age.
Like many degenerative diseases, AMD can be caused by several risk factors. Age is obviously a major factor, but genetics and the environment also play big roles. For example, white Americans over the age of 50 are twice as likely to have AMD (2.1% of the over 50 population) than people of any other race (0.9%).
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According to the authors of a new study published in BMJ, there is almost no research on how air pollution can affect our chances of getting AMD. Some studies show that exposure to air pollution can increase the risk of eye problems such as conjunctivitis and dry eye. Smoking is also thought to double the risk of developing AMD.
Researchers based in China examined national health data from the country and forwarded them with air quality data. The health records of people over 50, in addition to determining whether they were ever diagnosed with AMD over an 11-year period through 2010, were used roughly to estimate where they live, based on where they often are received medical treatment. And for air quality, they focused on two major sources of air pollution, often emitted by motor vehicles: nitrogen dioxide (NO2) and carbon monoxide (CO).
People were divided equally into four groups based on how high their average daytime NO2 and CO exposure levels were. According to the authors, those who lived in areas with the highest NO2 and CO content were almost twice as likely to be diagnosed with AMD than people living in the lowest NO2 and CO exposure area.
"This study shows exposure to air pollution as a risk factor for AMD," the authors wrote.
There are several caveats to this study, as always. One is that population studies like this can only show a link between two things, not to show that one causes the other, and although the authors noted other risk factors for AMD, such as age or high blood pressure, they failed to trace the history of smoking.
Another important consideration is that China has much higher n Medium-sized air pollution than many other countries, including the United States And since researchers have found no increased risk of AMD for more moderate levels of NO2 or CO, there may be areas in the world where these findings do not The relative risk of getting AMD was also low in the study, with only 0.036 percent of people in a sample size of nearly 40,000 developing the condition over the study period.
Therefore, China is apparently one of the largest countries in the world, with more than 1.3 billion inhabitants. This is also not the only country that is concerned about high levels of air pollution – much of Asia, including more populous India, is also struggling with poor air quality. And even in countries with relatively good air quality, such as the UK, car exhaust is still thought to contribute to thousands of preventable deaths each year.
Because the retina is related to the central nervous system, the effects of air pollution on the brain may exceed AMD – a study published in 2018 using much of the same data found an increased risk of dementia in the elderly that are most exposed to these pollutants.