A new study says that exposing children to bacteria and allergens in the first year of their lives might have a protective effect and cut their allergy risk by age three. Why is this and is this research credible?
The research, conducted by scientists at the Johns Hopkins Children’s Center, aimed to get a clearer picture over whether childhood exposure to allergens, things like dirt and dust, actually contributes to developing childhood allergies or whether it has a preventive effect. That’s because previous studies have shown mixed results.
Some research says that children who grow up on farms and are exposed to microorganisms tend to have lower allergy and asthma rates. At the same time though, other studies have shown that for kids living in the inner-city, high levels of allergens and pollutants, like the presence of roaches and dust, seem to contribute to allergy and asthma rates. These two facts seem to contradict each other, but this latest study says perhaps not.
Published in the Journal of Allergy and Clinical Immunology, the researchers looked at the health of 467 inner-city newborns from Baltimore, Boston, New York and St. Louis and tracked them for first three years of their lives. Throughout this time, researchers visited the home environments of each of the children and used standard tests to measure what types of allergens were present in their homes and the overall allergen levels. They also routinely tested the children for allergies and signs of asthma, as well as giving them physical exams. In addition, the researchers collected and analyzed the bacterial content of dust from 104 of the 467 infants in the study.
What they found was that infants who in their first year of life were exposed to mouse and cat dander, that is, material that is shed from an animal, as well as cockroach droppings appeared to have lower rates of wheezing at age three when compared to children who weren’t exposed to these allergens soon after birth. Interestingly, the effect was greater if the children had been exposed to all three allergens at an earlier age. For example, wheezing occurred in 51% of the children who weren’t exposed to any of the allergens compared to just 17 percent of children who grew up in houses where all three allergens were present in high levels.
The research also seemed to show that if a household had a greater variety of bacteria, children were less likely to develop things like dust allergies and wheezing by age three. Around 41% of allergy-free and wheeze-free children grew up in homes with the highest levels of recorded bacteria. Only 8% of children who suffered from both allergy and wheezing were exposed to these allergens during their first year.
To emphasize that first year-exposure appears to be crucial here, the study confirmed that children living in homes with the highest rates of bacteria and allergens were overall more likely to develop asthma and allergies. It was only when scientists focused on first year-exposure that the pattern emerged.
“Our study shows that the timing of initial exposure may be critical,” study author Robert Wood, M.D. of the Johns Hopkins Children’s Center is quoted as saying. “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.”
This appears to reconcile why children who grow up on farms are less likely to develop allergies that might be expected in that setting, whereas children in inner city areas where families work hard to keep their homes clean and tidy might be at greater risk.
The study did have some limitations of course, for instance that it only tracked allergy rates in children up to three years. That means all that we can really say from this study is that, up to three years-old, early exposure seems to significantly decrease developing allergies and asthma. Will that hold true over the long term? That’s something that the scientists will need to test, but it does fit neatly into the picture that has already emerged from other studies.
To be clear here, the researchers aren’t advocating that we allow children to play and live in squalid conditions. What they are saying is that allowing infants to be exposed to a normal environment (as opposed to the highly sterile one we may want to provide for our newborn children) might be beneficial because it could allow children to develop immunity at an early age.
What are your thoughts? Do you believe in letting your child get dirty, or are you in the clean camp? Let us know in the comments below.
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