Could the disinfectants that we commonly use to clean our homes cause our children to become overweight? Researchers for the Canadian Healthy Infant Longitudinal Development (CHILD) study analyzed the gut microbiota of more than 750 children aged 3–4 months, and looked at the children’s exposure to disinfectants, detergents, and eco-friendly cleaning products used in their homes. After controlling for a wide range of other potential factors, the results found a clear, dose-dependent link between the mothers’ reported use of disinfectant in the home, changes in the levels of some types of normal gut bacteria in their 3–4-month-old infants, and the children’s weight at age 1 and 3 years. In contrast eco-friendly cleaning products didn’t increase the likelihood of children becoming overweight.
"We found that infants living in households with disinfectants being used at least weekly were twice as likely to have higher levels of the gut microbes Lachnospiraceae at age 3–4 months,” comments Anita Kozyrskyj, Ph.D., a University of Alberta pediatrics professor, and principal investigator on the SyMBIOTA project, an investigation into how alteration of the infant gut microbiome impacts on children's health. “When they were three years old, their body mass index was higher than children not exposed to heavy home use of disinfectants as an infant." And while the researchers are not advocating that we all stop using our disinfectants, Dr. Kozyrskyj does suggest that they should not be overused.
The researchers report their results in the Canadian Medical Association Journal (CMAJ), in a paper titled, “Postnatal exposure to household disinfectants, infant gut microbiota and subsequent risk of overweight in children.”
Disinfectants, detergents, and other cleaning products are now ubiquitous in our homes, and their use has been associated with an increased risk of wheezing in both users and their children, the researchers report. Although there is relatively little data on any association between cleaning products and bodyweight, one study has found high urinary levels of triclosan in adolescents with higher adiposity. Another has shown that piglets exposed to aerosolized disinfectants demonstrate altered gut microbiota. “Indeed, concerns over the potential for antibacterial products to be too effective or even toxic has motivated use of “green” or eco-friendly alternatives,” the authors continue.
The CHILD research study birth cohort has been designed to assess the impact of indoor environmental exposures, including household cleaning products, on postnatal health. To further investigate any potential link between the use of different types of cleaning products and weight in children, the researchers analyzed data on the pregnancies, birth, and health of 757 infants, together with completed maternal questionnaires on aspects of health, home environment, including the frequency of use of different categories of cleaning products. The researchers also analyzed fecal samples from the infants aged 3–4 months, and followed their development, including measurements of height and weight.
Infancy is a key time in microbiome development, Dr. Kozyrskyj comments in a podcast that accompanies the publication. “We start with a fewer number species and they increase over the first year of life. The different kinds of species increase, some even decrease.” By about three years of age we each have a microbiome that we can “call our own”, and which remains with us through life. Microbiome changes caused by some environmental factors such as antibiotic use can change that microbiome, tend to be transitory, and the normal childhood pattern is then resumed.
In the reported study, after controlling for factors including breastfeeding, and antibiotic exposure, the results indicated a clear association between disinfectant use—but not other types of cleaning products such as detergents—and changes to infant gut microbiota composition. In particular, the gut microbiota of infants living in homes where there was a high use of disinfectants showed higher abundance of Lachnospiraceae bacteria, but reduced numbers of Haemophilus and Clostridium species. In contrast, infants living in homes where eco-friendly products were used had reduced abundance of Enterobacteriaceae, a class of bacteria that includes Escherichia coli. In contrast with disinfectant use, there was an inverse dose-response between frequency of use of eco-friendly products and the abundance of Enterobacteriaceae in the infants’ fecal samples.
After adjusting for multiple factors such as maternal weight before pregnancy, vaginal or cesarian delivery, and antibiotic exposure, the analyses indicated a clear, dose-dependent link between disinfectant use, increased abundance of fecal Lachnospiraceae a 3–4 months of age, and overweight at age 3 years. Further analyses indicated that this link was causal. “Evidence of statistical mediation with Lachnospiraceae abundance showed a role for this disinfectant-related change to gut microbiota in causing overweight,” the researchers write.
“We found frequent home use of disinfectant, as high as once daily, increased the chance of an infant having higher levels of a particular bacteria Lachnospiraceae in their gut microbiota, and also increased the risks of the infants becoming overweight by age three,” Dr. Kozyrskyj comments in the podcast. “These results suggest that gut microbiota were the culprits, and the association between disinfectant use and becoming overweight.”
In contrast, the link between eco-friendly product use, reduced fecal Enterobacteriaceae abundance, and reduced incidence of overweight at age three years didn’t appear causal. “Those infants growing up in households with heavy use of eco cleaners had much lower levels of the gut microbes Enterobacteriaceae,” Dr. Kozyrskyj notes. “However, we found no evidence that these gut microbiome changes caused the reduced obesity risk.” As she notes in the podcast, “Our analyses were controlled for other well-known factors that affect microbiota,” so it wasn’t those factors that explained any of the realists we obtained. In the case of the eco-friendly products, I must admit that we were a bit surprised.”
This lack of association between reduced levels of Enterobacteriaceae in the infants of mothers who use eco-friendly products and obesity indicate that another pathway is responsible. Dr. Kozyrskyj suggests these mothers may have generally healthier lifestyles, and eat more healthily during pregnancy, for example, so their children inherit a healthier microbiome.
“Antibacterial cleaning products have the capacity to change the environmental microbiome and alter risk for child overweight,” the authors conclude. They also note that that further research will now be needed. “Because this is a first study, confirmatory research in other cohorts is required," Dr. Kozyrskyj acknowledges. "Animal model research is also required. At this point, I would say that our findings suggest that households should not overuse disinfectants. I want to emphasize that our findings on the disinfectant use were at the higher end of use."
“Further study is required on the mechanisms through which household cleaning products alter gut microbial composition and the subsequent role this might have on metabolic disease,” the authors continue. Dr. Kozyrskyj comments that children in the study are now at eight years old mark, and the researchers plan to investigate the effects of being overweight at three years old on other health outcomes, such as insulin resistance, as they continue to grow. They are also looking at the effects of cleaning products on other health outcomes, such as asthma and allergic diseases, and expect to publish research on an association between the use of cleaning products and the development of asthma.