Is Brushing Your Teeth Harming Your Gut Microbiome?

In the 1960’s, the microbicide triclosan, was introduced in the United States, and soon after, human weight started to increase dramatically. For some time, researchers have wondered whether triclosan could have played a role in disrupting endocrine dysfunction and contributing to the obesity epidemic today.

In recent years, scientists have learned that changes in the composition of the gut microbiome can play a role in diseases, such as diabetes, metabolic syndrome, and obesity. Antibiotics are known to have an impact on the gut microbiome. "When you throw most antibiotics into humans, they are an atom bomb on the microbiota,” said Julie Parsonnet, MD, George Deforest Barnett Professor in Medicine and Professor of Health Research and Policy, Stanford School of Medicine.

Soon after triclosan was introduced, it was integrated into a wide range of household cleaning and personal care products including soaps and toothpastes. As recently as 2008, triclosan was detected in 75% of human urine samples. Scientists became concerned that the widespread use of triclosan could contribute to antimicrobial resistance and/or have an adverse effect on the human microbiome. In 2013, the FDA issued a proposed rule requiring manufacturers of antibacterial soaps and body washes to provide evidence within one year that their products containing triclosan are safe and more effective than plain soaps in preventing illness.

In response to public concern about both potential (but unproved) health and environmental toxicities, triclosan and its congener triclocarban were voluntarily removed from many commercial soaps in the United States, but are still found in some hospital cleaning products and the most common toothpaste in the United States, Colgate Total.  Triclosan is known to mitigate plaque burden and gingivitis.

So, should people be worried about the triclosan that they still come into contact with?  No, at least not with respect to effects on the human gastrointestinal microbiota, according to a study led by Dr. Parsonnet. The study, published in a recent issue of the American Society for Microbiology’s open-access journal mSphere, shows that soaps and toothpastes that contain the antibiotic triclosan do not have a marked influence on gastrointestinal or oral microbial communities or on human endocrine function.

In the double-blind, randomized, crossover study, Stanford investigators randomized 13 healthy individuals to use household and personal care products (toothpaste, hand soap, and dishwashing liquid) that either contained triclosan or did not contain triclosan for four months. After four months, individuals were switched to the alternative arm for another four months. The researchers analyzed blood samples for metabolic and endocrine markers, urine samples for triclosan, and stool and oral samples for microbiome composition. While triclosan-containing products had a significant impact on the levels of triclosan found in urine, exposure to triclosan did not have a significant impact on the oral or gut microbiome or on a panel of metabolic markers.

"There are a lot of people who are fearful of triclosan, but we didn't find anything to support that concern in our study at least with respect to the microbiota or endocrine function in adults,” said Dr. Parsonnet. “Some organisms were changed a little bit, but there was no major blow to oral flora or gut flora. When people are exposed to triclosan through normal household products, it does not cause a major blow to our microbial ecosystems. For people who are very fearful of triclosan, our study should be reassuring."

Dr. Parsonnet said more focused research is needed, particularly on oral flora, to assess whether the subtle taxonomic shifts that were observed have long-term influences on human health. She is currently involved in an epidemiologic study assessing the microbial and growth effects of triclosan in babies and pregnant women.

-Kate O'Rourke

Comments

[Steve Hawkins]

Hmm: Where is the pre 1960 control microbiome?

:/

[Carlos Rodriguez]

Sublethal concentrations of antibiotics have been implicated in triggering oxidative stress which may cause mutations leading to altered targets of antimicrobial drugs by inducing the SOS response (low doses of antibiotics serving as mutagenic agents): "Kohanski MA, DePristo MA, Collins JJ. Sublethal antibiotic treatment leads to multidrug resistance via radical-induced mutagenesis. Mol Cell. 2010 Feb 12;37(3):311-20". Could this be inconspicuously happening with triclosan?

In murine models (which may not necessarily correlate with humans) triclosan has been associated with liver tumors: "Yueh MF, Taniguchi K, Chen S, Evans RM, Hammock BD, Karin M, Tukey RH. The commonly used antimicrobial additive triclosan is a liver tumor promoter. Proc Natl Acad Sci U S A. 2014 Dec 2;111(48):17200-5".

[Dave B]

Did I miss something?
This article published same day seems to be saying the opposite?
http://oregonstate.edu/ua/ncs/archives/2016/may/common-antimicrobial-agent-rapidly-disrupts-gut-bacteria

[mBiosphere]

You're right that the PLOS One report released around the same time came to a different conclusion. Different animal models, drug concentration + administration, and bacterial diversity measurements can result in two scientists addressing the same question arriving at different conclusions. This is one reason repeated studies are important!