In the modern world, a greater emphasis on cleanliness has resulted in the proliferation and frequent use of household disinfectants and detergents. Previous studies have shown that overexposure to household cleaners is linked with a greater risk of respiratory sicknesses, but now, a new study published in the Canadian Medical Association Journal has uncovered evidence that children living in houses with frequent household cleaner use are more likely to be overweight by age 3.
The same study also found that the link is largely mediated by changes in the constitution of gut bacteria in children due to exposure to household cleaners.
The particular study is part of larger project composed of a number of studies performed over the past 3 years. The goal of the larger project is to shed light on the relationship between the microbial environments children are raised and the future health. All in all, the researcher determined that frequent use of household disinfectants were highly associated with elevated levels of the gut bacteria Lachnospiraceae, which in turn were associated with a higher risk of being overweight by the age of 3. Conversely, the study found that the use of “eco-friendly” products, cleaning products that do not rely on the use of disinfectants to kill bacteria, were associated were a lessened rates of obesity by 3 years of age. In other words, the study seems to suggest that some exposure to bacteria in infants can actually be developmentally beneficial and that too sterile of an environment can lead to health problems later in a child’s life.
A 3-Year Long Study
All in all, the study followed a cohort of over 3,000 pregnant women and the three years following childbirth. 3-4 months after birth, the researchers obtained a fecal sample from each infant and administered each mother a self-response survey on their cleaning habits. Included in the survey were questions about their personal health, home environment, and household cleaner use. At ages 1 and 3, each child weight was measured and determined to be overweight or not. During this process, a number of initial subjects were excluded from the final analysis for reasons such as lack of accurate health records, in vitro births, or low birth weights. The final analysis consisted of a sample size of 757 infants which was representative of the demographics of the original larger cohort.
According to the final analysis, household disinfectant use, in general, was not significantly correlated or related to a higher risk of obesity. However, higher use of disinfectants was highly associated with greater amounts of fecal bacteria Lachnospiraceae, and unadjusted results suggest top 30th percentile of disinfectant use was correlated with a higher BMI, but not significantly with obesity. The study also found that higher fecal amounts of Lachnospiraceae were significantly associated with obesity at ages 1 and 3.
Once the study adjusted initial results for higher levels of Lachnospiraceae, the correlation between top 30th percentile use of disinfectants and higher BMI scores vanished. The high association between disinfectant use and fecal amounts of Lachnospiraceae, the high association between fecal amounts of Lachnospiraceae and risk of obesity, and the diminishment of the association between top 30th percentile of disinfectant use and a greater BMI score once controlled for fecal amounts of Lachnospiracea, indicate a strong mediating effect by the family of bacteria. In other words, increased disinfectant use is associated with more Lachnospiraceae, more Lachnospiraceae is associated with risks of obesity, but disinfectant use is not significantly associated with higher rates of obesity, indicating that the causal pathway from disinfectant use to obesity is strongly mediated by the presence of Lachnospiraceae.
Previous studies have shown links between obesity-related metabolites and the presence of colonies of Lachnospiraceae in the gut, yet the causal mechanisms that explain this relation are still not well understood. Experiments in mice have also indicated that colonies of Lachnospiraceae are associated with higher white adipose tissue mass and insulin resistance. The current study is illuminating as it shows the effect that household environments have on the microbial constitution of infants’ intestines, and how that effect contributes to weight-related problems later in life.
Additionally, the study pointe out that higher use of “eco-friendly” cleaning products is associated with decreased risk of obesity by age 3. Eco-friendly products are known to be effective against E. coli, and lessened amounts of E. coli gut bacteria are associated with less adiposity in toddlers. However, the researchers also found that the use of eco-friendly products did not seem to have an effect on gut microbe constitution, indicating that the causal pathway from eco-friendly use to decreased risk of obesity is likely due to factors other than gut microbial constitution. For example, the study also found that mothers who used more eco-friendly products were likely to be more educated and have a history of good health, meaning they likely raise their children with relatively healthy habits.
Bacteria get a somewhat bad rep, for understandable reasons. But this study seems to indicate that compulsive use of bacteria-killing disinfectants can have a significant effect on the constitution of gut bacteria in infants. These changes in gut microbe concentration can, in turn, lead to higher risks of obesity by the age of 3. In many ways, these results can be seen as confirmation of the hygiene hypothesis of metabolic disorders. In a nutshell, the hygiene hypothesis states that proper development of the metabolism requires moderate exposure to certain kinds of bacteria. Without that exposure at a crucial age, a child’s metabolism can be thrown off track. It is also though the hygiene hypothesis has something to do with the presence of allergies and autoimmune disease in humans.
So perhaps a lesson to draw is that new parents should not be overly concerned with exposing their young children to certain kinds of bacteria. Exposure to moderate levels of bacteria seems necessary for building a proper immune system and metabolism; after all, how is the immune system supposed to get stronger if it never has a chance to act?
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