"Having a pet dog…can help reduce the child's chances of developing allergies and becoming obese in later years," claims the Daily Mirror, in a somewhat misleading report.
The researchers carried out a range of tests on faecal (poo) samples taken from infants to assess the levels and composition of the bacteria in their guts.
Gut bacteria is widely known to play an important role in future health. Infant gut bacteria is thought to be influenced by several factors including the method of birth delivery, drinking breast milk versus formula, and treatment of the mother with antibiotics. So the hypothesis that furry pets could boost infant immunity has increasingly been discussed.
Overall, the study found that the composition of gut bacteria was richer and more diverse in infants who had been exposed to pets both in the womb and after birth. But whether or not this observation actually has any effect on health outcomes wasn't explored.
This Canadian study was carried out by researchers from several institutes including the University of Toronto, the University of Alberta and the University of British Columbia. It was funded by a grant from the CIHR Canadian Microbiome Initiative.
Both the Mirror's and the Mail Online's headlines were misleading, wrongly giving the impression that researchers had looked at allergy and obesity rates in later life. This was not the case.
The body of reporting in both sources was much more balanced and had greater focus on the gut bacteria.
This was an analysis of a subgroup of infants from a larger prospective cohort study: the Canadian Healthy Infant Longitudinal Development Study (CHILD). It wanted to assess whether a baby's exposure to pets while in the womb and after birth has any impact on their gut bacteria.
Giving antibiotics to a mother during labour can disrupt her baby's gut bacteria, so antibiotic use was also analysed – as well as the method of delivery: caesarean (elective versus emergency) and vaginal delivery (with or without antibiotics).
Prospective cohort studies such as this are useful for understanding whether a link between an exposure (in this case, pets) and an outcome (a change in infant gut bacteria) exists. However, the challenge with this study design is that it isn't able to fully rule out the involvement of other confounding environmental and lifestyle factors, such as diet.
Although a randomised controlled trial (RCT) is the best way to validate any findings, it certainly wouldn't be practical (let alone ethical) to expose parents and their infants to pets against their will. The study also doesn't explore whether levels of infant gut bacteria have any effect on long-term outcomes.
This study analysed a subsample of 753 infants from the CHILD study, which enrolled pregnant women between 2009 and 2011.
The mothers were given a questionnaire about pet ownership during their second or third trimester of pregnancy, and three months after birth.
Exposure to pets was categorised into:
The category assessing "only postnatal pet exposure" was found to only include seven mothers, so it was excluded from subsequent analysis.
Gut bacteria in faecal samples was analysed for infants with complete data on prenatal and postnatal pet exposure (n=746).
Data on a range of potential confounding factors was also collected:
The data was analysed to test for any links between pet exposure and the composition of gut bacteria.
Statistical analysis was carried out to compare four different birth scenarios:
The analysis was adjusted to take into account the confounders.
Out of the 746 infants, 46.8% of households owned furry pets during and after pregnancy. The majority of pet owners had dogs, closely followed by cats.
Overall, the composition of gut bacteria was richer and more diverse in infants who had been exposed to pets during both the prenatal and postnatal period. In particular, there was an abundance of two bacteria, ruminococcus and oscillospira. Previous research has linked each of these strains to improved "gut health".
The researchers add that previous studies have found an association between lower levels of these bacteria and a greater likelihood of childhood allergies and obesity. But this hypothesis was not investigated in this study.
The study also found that a baby's exposure to pets while in the womb resulted in lower levels of streptococcal bacteria in their gut.
The researchers concluded: "Our findings highlighted the differential impact of pet exposure on infant gut microbiota following variant birth scenarios; however, in common, the abundance of ruminococcus and oscillospira were found to be increased independent of other factors.
"In addition, our finding of reduced streptococcal colonization with prenatal pet ownership may lower the risk for childhood metabolic and [allergic] disease. Further research is needed to link the pet-related microbiota changes with health outcomes of infants in the CHILD cohort, as well as in other populations."
This subgroup analysis of babies from a large Canadian birth cohort assessed whether exposure to furry pets before and after birth has any impact on infant gut bacteria. Overall it found that exposure to pets while in the womb and after birth was linked with richer and more diverse gut bacteria.
The researchers say that several studies in the past, including their own, have found a link between richness of gut bacteria and both the development of allergies and the development of obesity. Therefore these findings may be taken to imply that pet exposure could protect against allergy and obesity in infants – as in media reports. However, later child health outcomes, including the development of allergy or obesity, were not investigated in this study.
This short term study only looked at the composition of gut bacteria in infants at three months of age. It would be useful to see how long-term exposure to pets affects gut bacteria in individuals and whether the same results are observed, and to see whether there is any link with other health outcomes.
The study also found that pre-natal exposure to pets resulted in lower levels of streptococcal bacteria. Many women carry group B streptococcus without symptoms, and this can sometimes cause infection in newborns, hence the relevance of this link. However, again this has not been investigated further.
There is also the possibility that any links between pet ownership and bacterial levels are being influenced by other environmental and health-related confounders. Bacterial levels may not necessarily be a direct result of the pets. Also, bear in mind that the results of this Canadian study may not necessarily apply to the UK or other countries.
These findings pave the way for future research around pet exposure and health outcomes in individuals, especially around allergies. However, this research is too early in stage to recommend that parents-to-be have a pet to protect their children against allergies, and certainly not against obesity (although walking your dog could be good exercise!).
Breastfeeding children and minimising their exposure to tobacco smoke will also reduce their allergy risks. And regular exercise and a healthy diet should prevent a child from becoming obese.
Read more healthy weight advice for parents.