Asthma is one of the most common diseases among children, affecting roughly one in every eleven kids. It’s long been known that poor children living in impoverished city neighborhoods are more likely to suffer from higher rates and worse cases of asthma compared to kids that grow up in higher-income areas or in rural environments—but the causes of the increased risk are still unknown.
A new study from Johns Hopkins Children’s Center, published today in the Journal of Allergy and Clinical Immunology, confirms that data, adding one slightly unpleasant, but hopeful, twist to our existing knowledge of what makes kids sick.
Researchers followed a group of 467 children from birth to 3 years of age with high risk for asthma (living in an area where more than 20 percent of residents are below the poverty level and with a parent with allergies or asthma) in four urban areas: Baltimore, Boston, New York City, and St. Louis. The kids were tested at certain times for specific allergies: milk, eggs, peanuts, cockroaches, dust mites, dogs, cats, and mice. Researchers also analyzed the bacteria from dust collected from the 104 homes.
The study found that children exposed to a perfect storm of bacteria and allergens—specifically (trigger warning: gross) mouse and cat dander and cockroach droppings—had lower rates of wheezing at 3 years old, but only when the exposure took place before 1 year of age. It’s important to recognize that recurrent wheezing isn’t the same as asthma; only around 60 percent of these wheezers will go on to develop asthma by 6 or 7 years old.
“Exposure to allergens early on isn’t necessarily associated with the development of asthma,” said Dr. Peter Gergen, from the National Institute of Health, who worked on the study. “It’s once you become sensitized to them and develop an allergy against them, then it makes your asthma much worse. There’s still no definite answer for what causes it.”
The findings give additional credibility to what’s known as the Hygiene Hypothesis and the trend of introducing bacteria earlier in response to a cultural over-cleanliness, which devotees say wipes out good germs that contribute to a kind of bio-balance and keep us healthy. From the FDA:
“Scientists based this hypothesis in part on the observation that, before birth, the fetal immune system’s “default setting” is suppressed to prevent it from rejecting maternal tissue. Such a low default setting is necessary before birth—when the mother is providing the fetus with her own antibodies. But in the period immediately after birth the child’s own immune system must take over and learn how to fend for itself.”
Two points to take note of here. One, the study is the first of its kind to look at the effects of a bacteria/allergen exposure in combination with one another. And most notably, they found that kids that were both wheeze- and allergy-free had (from the release, emphasis mine) “grown up with the highest levels of household allergens and were the most likely to live in houses with the richest array of bacterial species. Some 41 percent of allergy-free and wheeze-free children had grown up in such allergen and bacteria-rich homes. By contrast, only 8 percent of children who suffered from both allergy and wheezing had been exposed to these substances in their first year of life.”
On other words, the more dander and bacteria, the fewer sick kids.
Two, the study gets at the best time for exposure.
Author Robert Wood, M.D., called the timing of the initial exposure “critical” in a news release. “What this tells us is that not only are many of our immune responses shaped in the first year of life, but also that certain bacteria and allergens play an important role in stimulating and training the immune system to behave a certain way,” he said.
Will crunchy parents be running to the pet stores for roach farms? Not so fast. When asked, “Why cockroach, mice and cats? Why not dust and dogs?” Gergen explained.
“It’s not the allergens themselves, but the mix of the allergens and bacteria. The particular bacteria that happened to be helpful just happened to be associated with those three allergens. At this point, we don’t understand why. Whether cockroach and mice are always associated with this bacteria, we can’t yet say.”
The researchers are continuing to follow the children in the study, who are now 7 years old. With in the next year, they’ll know which children have asthma. If the allergens/bacteria combo really did result in less asthma, then it might be a clue into the manipulation of environmental factors that could lower risk overall.