Infants and pets not a recipe for asthma
Keeping furry domesticated animals in a household with toddlers doesn’t lead children to develop asthma in their early school years.
Children under the age of two who live with dogs, cats, birds and hamsters or other rodents are no more likely to develop asthma at the ages of 6-10 than kids who don't have furry critters underfoot in their homes.
The finding, from a large European study based on 11 smaller studies from seven countries, means that health personnel no longer need to push parents to stop keeping pets to protect their children from developing asthma.
The countries involved in the study were Norway, Sweden, Denmark, Great Britain, Germany, the Netherlands and Spain.
Two rounds of questions
The parents of some 11,000 children first answered a questionnaire when their children were two years old. Parents responded to the questionnaire again when the kids were older, although the ages varied from study to study.
In some studies the children were six, while in others they were eight, nine or ten. The prevalence of asthma remained steady thoughout.
This steady prevalence of asthma in spite of the difference in the children's ages indicates that the second round of questions wasn’t posed too early, before the children had developed asthma, according to the article in PLoS ONE, which published the findings.
The study covered allergic and non-allergic asthma. Allergic asthma comprised all the cases where the children also had allergic reactions to foods or airborne substances.
The non-allergenic type of asthma has no known cause.
The scientists also found there was also no increase in hay fever cases. In other words, pets don’t pose a respiratory or allergenic health threat for small children, according to the study.
In fact, in some cases, furry pets appear to help protect children. The results indicate that youngsters with dogs and rodents at home run less risk of becoming oversensitive to substances in the air believed to trigger allergies.
Dogs also provide protection against substances that can trigger food allergies, the article asserts.
Better on a farm
Why then, are there still people who are allergic to pets? "We don’t know for sure. It’s probably a mix of genetic disposition and environmental factors," said Karin C. Lødrup Carlsen in an e-mail.
She is first author of the article and a part-time professor at a clinic for women and children at Oslo University Hospital, Ullevål.
Lødrup Carlsen also pointed out that other studies show that children who grow up on farms also have fewer allergies.
She thinks that the findings that farm kids have fewer allergies are probably not due to the animals per se. But animal husbandry exposes children to a much broader flora of bacteria and microorganisms than kids encounter in cities, she says.
This biological micro-diversity has an effect on our immune system, making it more capable of tackling our environment. This curbs the development of asthma and hay fever.
Previous studies of children and allergy to animals have been based on different answers from a number of studies, each with their own suppositions and definitions. The differing designs may explain the conflicting results.
In contrast, the authors of the PLoS ONE study extracted their data from a large, common database. The information was correlated, or harmonised. This meant the data was analysed in the same way in all seven countries, and allergy diseases were defined identically.
The impressive number of participants enabled the medical scientists to rule out other possible contributing factors. Factors such as a history of asthma and allergies in the family, a mother who smoked during her pregnancy or housing conditions could influence the results or suggest a plethora of alternative causes, for example.
The study was so comprehensive it gave the researchers a chance to focus on smaller details in the results.
For example, they were able to zoom in on special age groups from newborns to two-year-olds. They discovered that there were no special, shorter time intervals in which tots were more sensitive to their furry animal friends.
The researchers were also stricter with their definitions of what can be designated as asthma. It wasn’t enough if parents noted a characteristic wheeze in their children’s breathing.
The children had to meet two out of three special criteria: The asthma had to be diagnosed by a doctor, asthma medications had been used in the past 12 months and asthma symptoms were present in the past 12 months.
Translated by: Glenn Ostling
- Karin C. Lødrup Carlsen et.al: Does Pet Ownership in Infancy Lead to Asthma or Allergy at School Age? Pooled Analysis of Individual Participant Data from 11 European Birth Cohorts, PLoS ONE, august 2012, Volume 7, Issue 8