Common consumer chemical linked to liver cancer in mice

Researchers in the US have warned that long-term exposure to the very common synthetic compound, triclosan, can promote liver fibrosis and cancer in mice, and the mechanisms at play mean this finding could also apply to humans.

Developed 50 years ago, triclosan’s history as an antimicrobial additive to our various cleaning and health products has been mired in controversy. Added to a number of common hygiene products and detergents, it makes its way into our bodies over many years of exposure, with research finding traces of it in 97 percent of breast milk samples taken from lactating women, and in the urine of nearly 75 percent of people tested. According to Steve Connor at The Independent, about 1,500 tonnes of the stuff is produced around the world each year, and a lot of that ends up in our rivers and streams.

While it’s been proven to fight gum disease and remove all kinds of harmful bacteria from our skin and mouths, several studies have linked triclosan to disrupted hormonal development and impaired muscle contraction, increases in allergies and an increase in antibiotic-resistant bacteria. And now new research suggests that we add liver cancer to the list of possible side effects.

Researchers from the University of California, San Diego's School of Medicine fed 3 grams of the substance to lab mice for six months to observe the effects on their health. This timeframe is roughly equivalent to 18 years in humans, and for comparison, one gram of toothpaste contains about 0.03 percent triclosan. 

The results showed that the mice that were fed triclosan ended up being more susceptible to liver tumours trigged by other chemicals known to have carcinogenic properties. The researchers also found that the tumours in these mice were larger and more frequent than those in mice that were not exposed to triclosan.

Led by Robert H. Tukey, a professor in the departments of Chemistry and Biochemistry and Pharmacology at the university, the team says that triclosan appears to interfere with a particular protein called the constitutive androstane receptor, which is responsible for clearing foreign chemicals out of our bodies. If this protein cannot do its job properly, the liver is put under a lot of stress, and its cells will eventually become fibrotic, which causes severe scarring of the liver tissue. As the mouse livers became more and more fibrotic over time, and they continued to be exposed to triclosan, the combination eventually was seen to promote tumour formation.

While the results of animal studies should always been taken with a grain of salt when figuring out where humans fit in, the team says that this process is relevant to how triclosan messes with our own molecular make-up. They published the results in the journal Proceedings of the National Academy of Sciences.

"Triclosan's increasing detection in environmental samples and its increasingly broad use in consumer products may overcome its moderate benefit and present a very real risk of liver toxicity for people, as it does in mice, particularly when combined with other compounds with similar action," said Tukey in a press release.

"We could reduce most human and environmental exposures by eliminating uses of triclosan that are high volume, but of low benefit, such as inclusion in liquid hand soaps,” added one of the team, toxicologist Bruce D. Hammock. "Yet we could also for now retain uses shown to have health value — as in toothpaste, where the amount used is small.”

According to The Independent, this and several previous studies on the possible health effects of triclosan have put it under scrutiny by the US Food and Drug Administration (FDA), but so far there's not enough evidence for them to restrict its use in consumer products. Eryk Bagshaw at The Sydney Morning Herald reports that in 2010 the European Union banned triclosan in all products that come into contact with food, but still allows toothpaste containing up to 0.3 percent of it. The Australian Department of Health's National Industrial Chemicals Notification and Assessment Scheme classifies it as a poison at levels any higher than this.

Popular toothpaste brand, Colgate, still uses triclosan, with Colgate Australia spokeswoman, Tamara Daran, telling Bagshaw in August, "Regarding carcinogenicity [cancer causing chemicals], three studies in three different animal species were reviewed by the US FDA - and later regulators in Europe, Canada and Australia. All concluded that triclosan in Colgate Total is safe."

Meanwhile, Procter & Gamble, one of the biggest consumer product manufacturers in the world responsible for brands such as Oral B and Pantene, announced in late 2013 that it would be removing triclosan from all of its products.

Of course, without direct evidence, it’s too soon to panic, as Oliver Jones of the University of Melbourne in Australia told Connor at The Independent, “Firstly, the mice used in the study were primed with a tumour-promoting chemical before being exposed to triclosan, which humans would not be. And the concentrations of triclosan used were much higher than those found in the environment.”

Would be worth keeping an eye on future research though. In the meantime, you can browse this list of products containing triclosan, for your own peace of mind.

Sources: EurekAlert, The Independent, The Sydney Morning Herald