Dear EarthTalk: Is it true that asthma rates in the U.S. have doubled in the last three decades? What's behind this troubling trend and what can we do to reverse it? -- Patrick, via e-mail
Asthma is on the rise across the U.S., doubling since the 1980s. According to the Environmental Defense Fund (EDF), most people who develop asthma likely have a genetic predisposition but also probably experienced “critical environmental exposures during the first years of life.” Asthma rates are highest in urban areas where auto and industrial emissions make for difficult breathing. But air quality in U.S. cities has improved in the last few decades, leaving researchers puzzled as to what’s behind the trend.
One theory is that better hygiene in developed countries means that Westerners have less exposure to bacteria, viruses and parasites, altering our immune response with the result being increased risk for allergic diseases like asthma. Indeed, Western asthma rates are 50 times higher than in rural Africa. While this “hygiene hypothesis” may be part of the story, researchers believe that there are also other factors.
Some studies have shown a correlation between asthma and obesity, though a direct link is hard to prove. Other research has shown that psychological stress can trigger asthma attacks in those already predisposed. Dr. Harold Nelson, professor of medicine at the National Jewish Health in Denver, explained in a 2009 New York Times blog post that increased acetaminophen (i.e. Tylenol) use in young children, exposure to household cleaning sprays, and lack of Vitamin D also likely contribute to rising asthma rates. But how?
Pediatricians recommend against giving young children aspirin today, given the increased risk of Reye’s syndrome, so many parents now use acetaminophen to relieve pain and reduce fever. But acetaminophen lowers levels of the antioxidant glutathione, resulting in an increased asthma risk. A 2008 study found that use of acetaminophen in the first year of life was associated with a 46 percent increase in the prevalence of asthma symptoms among a study group of 200,000 six- and seven-year-olds.
In regard to household cleaners, frequent inhaling of the spray mist from glass cleaners and air fresheners among other products irritates the lungs and increases the risk of developing asthma. A 2007 study found that European adults who used spray cleaners four days a week faced double the risk of developing asthma symptoms, while weekly use of cleaners increased the risk by 50 percent.
The link between Vitamin D deficiency and asthma comes from several studies on the topic over the last decade showing that low levels of Vitamin D in pregnant mothers result in more asthma in offspring. Those who spend lots of time indoors are particularly vulnerable to Vitamin D deficiency, as exposure to sunlight increases the body’s ability to produce the important nutrient.
Dr. Nelson says that people can take steps to lower their exposure to these “new” asthma risk factors. For one, forego spray cleaners and air fresheners for liquids and pump sprays that don’t produce a fine mist. Pregnant women might consider Vitamin D supplements. And parents should discuss pain relievers with their doctor and consider alternating different types so kids don’t get overexposed to any particular one.
CONTACTS: EDF, www.edf.org/health/air/asthma; “New Risks Linked to Asthma Rise” (New York Times, 2/12/09), well.blogs.nytimes.com/2009/02/12/new-risk-factors-linked-to-asthma-rise.
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