Much research has been done to identify risk factors and protective factors for asthma in an effort to understand the underlying causes of the disease. We know the following are associated with a higher risk of children developing asthma:
- Cigarette smoke exposure during pregnancy or early childhood,
- Lack of breastfeeding in early life,
- Excessive use of early life antibiotics,
- Premature birth,
- Caesarian birth,
- Excessively clean environments (disinfectants, antibiotic soap).
These conditions and exposures combine with genetics to make a person more likely to develop asthma. Researchers have also been able to identify early life exposures that are protective against the development of asthma, even in susceptible children. These include:
- Exposure to farm animals,
- Fewer antibiotics,
- Longer breastfeeding,
- and a vaginal delivery.
The protective effect of farm animal exposures seems to fall inline with the hygiene hypothesis. This is the idea that due to our concern about our children coming in contact with dirty things, their immune systems never get the chance to properly develop. Farm animals carry bacteria, parasites, dust, and dirt and so they activate our immune systems and help them to develop. Researchers from Sweden wondered if the protective effect of farm animals is also seen with families who have household pets like dogs. There are more people who own or can own dogs than those who have farm animals, in part due to cost, and so if the dogs offer some form of protection from developing asthma then this may be a useful strategy for offering protection to children who are at higher risk of developing asthma.
The research, published in the Journal of the American Medical Association – Pediatrics, analyzed the medical records of all children in Sweden (around 1.1 million kids) and calculated how often those with dogs versus those without dogs developed asthma by the age of 6. The unique part of this study is the cohort of people used. In Sweden, all people have a unique identification number where all the information about their trips to the doctor are recorded. The researchers then have access to this information (it’s all anonymous) and is a very powerful database. In addition to patient information, anyone who has ever owned a dog has to register it and so they have information about which patients have a dog and when they got the dog. When the researchers crunched the numbers, children who were exposed to a dog during their first year of life had a 13% decreased risk of developing asthma. When they were exposed to the dog within the first 3 years of life this lessened the protective effect to a 10% decreased risk. In the study, exposure to farm animals was associated with a 52% decreased risk of developing asthma, a much greater level of protection. The results may be important to families who are looking at getting an animal but don’t know when it is appropriate to introduce that animal to their children. More evidence is coming out all the time that shows children should be exposed to animals, dirt, and bacteria in order to develop a proper immune system and prevent the development of asthma and other chronic diseases.