There are well-documented mental health benefits to pet ownership, as much research has shown. Indeed, we know there are some physical benefits as well, as dog owners tend to have more active lifestyles. Yet when it comes to conditions like allergies, we tend to think of pet ownership as exacerbating, not alleviating them.
Hence, a recent study published in the journal PLOS One might come as a surprise. The study, published Wednesday, found that children raised with cats and dogs early in life had a 13 to 16% lower risk of developing all food allergies than their counterparts who did not own pets.
Children who were exposed to dogs early in life were less likely to have nut allergies.
The researchers engaged in an exhaustive survey, studying 65,000 Japanese children with a questionnaire-based survey. They found that children who were exposed to dogs either during fetal development, early infancy, or up to the age of 3 years old were less likely to have nut, milk and egg allergies.
This wasn't true for other pets that weren't cats and dogs. Indeed, the same research found that children exposed to hamsters during this same period had an increased risk of nut allergies. Yet children who were exposed to cats during their early years were likewise less likely to develop specific allergies — namely, allergies to wheat, soybean and egg.
While the study is not the final word on the issue — the authors note "further studies using oral food challenges are required to more accurately assess the incident of food allergies" — it reinforces preexisting research on the seemingly bizarre ways that cats influence human development. Last year a study from the Journal of Psychiatric Research found a link among men between cat ownership in childhood and psychosis, one that could be caused by Toxoplasma gondii (T. gondii), a nasty protozoan best known for causing the disease toxoplasmosis. On the other hand, pet ownership has also been scientifically linked to a multitude of health benefits for humans including reduced risk of coronary artery disease, a reduction in stress levels and increased physical activity, lowered blood pressure among couples engaged in stressful work and improved cardiovascular disease survival among older adults (aged 65 to 84 years old) diagnosed with hypertension.
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In addition to adding to the growing body of scientific literature about pets and human health, the PLOS One: Children study also reinforces earlier research about the role of the environment in developing allergies. It is specifically reminiscent of the counterintuitive allergy research of German pediatrician and allergy specialist Dr. Erika von Mutius. Von Mutius repeatedly found that exposure to farmyard dirt, dust and the various aerosols that fly off of animals helps children in their respiratory development.
For example, in one 1994 study, von Mutius studied for asthma, atopy, bronchial hyper responsiveness (BHR) and hay fever among more than 5,000 9- to 11-year old children in West Germany and more than 2,600 in East Germany. Although epidemiologists had assumed that East Germans would have more asthma because of higher air pollution rates, the opposite was true. The study prompted a paradigm shift in epidemiological thinking about asthma.
Overall in her research, von Mutius discovered that young children in Germany, Austria and Switzerland who are regularly exposed to farmyard dirt and dust develop asthma and hay fever much less frequently.
"Experts once told Erika to tone down her supposedly radical suggestions that various 'nasties' might have protective qualities. Today, however, the same views she forwarded then are deeply engrained in literature on asthma and allergies."
Prior to von Mutius' research, epidemiologists generally advised that children be kept away from supposedly "unhygienic" influences like farms or around animals like dogs and cats. Dr. Fernando Martinez, director of the Respiratory Sciences Center at the University of Arizona in Tucson, alluded to this when commenting to Lancet.
"Experts once told Erika to tone down her supposedly radical suggestions that various 'nasties' might have protective qualities," Martinez told the publication. "Today, however, the same views she forwarded then are deeply ingrained in literature on asthma and allergies."
Allergic reactions are, like asthma, auto-immune responses. So why would exposure to allergens or pollutants result in lower rates of auto-immune responses? One theory is that auto-immune responses may result from environments that are too sterile, in that the immune system doesn't have enough to "do," to put it in layman's terms. This is the principle behind allergy immunotherapy, a well-established process whereby allergy sufferers are given tiny doses of the allergen that affects them, doses that increase each week; over time, their body adapts and becomes less sensitive and therefore less allergic. Immunotherapy is often given for pollen allergies or cat allergies.
Of course, this does not mean that all of the supposedly "nasty" exposures somehow result in health. As the authors of the PLOS One: Children study note: "fish, fruit, crustacean, and soba allergies showed no significant differences in association with exposure to any pet species." Similarly, "No significant differences were found in the associations between exposure to turtles or birds and the incidence of any specific food allergies until the age of 3 years."
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