Lipstick chemical 'may damage muscles'

"Antibacterial soap may hinder muscle function," reports The Daily Telegraph. The Daily Mail tells us of a "Lipstick chemical alert" and that an ingredient in hundreds of household products "causes heart problems".

These alarmist claims are based on a study in mice and fish that aimed to investigate the potential risks to muscle functioning of triclosan. Triclosan is a chemical that is used to prevent bacterial infections and is added to a wide range of products from lipstick, face washes and toothpaste to shoes, carpets and bedding.

The researchers did find that exposing mice and fish to certain doses of triclosan reduced muscle grip in mice and reduced swimming distance in fish.

Researchers also found that triclosan exposure disrupted a biological process known as excitation–contraction coupling (ECC). ECC describes a set of processes when electrical impulses sent from the brain are converted into the mechanical contractions of heart or skeletal muscles. Disruption or problems with ECC in heart muscles can be potentially serious as this could lead to heart failure.

Importantly, the study only tested the effect of the substance on mice and fish. Caution should be exercised when trying to apply the findings to humans. In addition, doses given in the study may not reflect doses contained in normal household products, so there is no need to throw away your lipstick just yet.

A number of studies have found that levels of triclosan can be found in drinking water and further research may be warranted to assess any potential long-term effects on humans.

Where did the story come from?

The study was carried out by researchers from the Universities of California and Colorado, US and was funded by grants from the US National Institutes of Health, Muscular Dystrophy Association and JB Johnson Foundation. The study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS).

The headlines and images used by The Daily Telegraph and Daily Mail may be misleading as they give the impression that the study was carried out in humans, which wasn’t the case. Reassuringly, both papers go on to report that the research was carried out in animals.

What kind of research was this?

This was an animal-based study testing the effects of different doses of a chemical substance, triclosan, on the muscle functioning of mice and the swimming performance of a type of fish. Testing high doses of chemicals like this on laboratory mice and fish is a widely used method of exploring the potential toxic effects of high doses.

The researchers say that no studies have looked at the effects of triclosan on muscles before.

What did the research involve?

The researchers conducted three tests on living mice and fish to look at whether triclosan reduced the ability of skeletal and cardiac muscle to function normally. In the first experiment, anaesthetised mice were given one of three doses of triclosan (6.25, 12.5 and 25mg/kg) and their cardiac response was measured using pressure volumes.

Second, to test the effects on skeletal muscle, a group of mice were given a single dose of triclosan and their grip strength was measured for up to an hour after the dose was given. In the third experiment, a group of fish (flathead minnows – a type of fish that has been used in previous experiments to test water pollutants) were exposed to three different doses of triclosan for up to seven days and swimming performance was assessed using video monitoring of the number of times they crossed a line in the tank.

The researchers compared the results of the experiments to either baseline values before a dose was given or to mice who acted as controls. Additionally, researchers looked at the hearts and skeletal muscles of dead mice to investigate the effects of triclosan further. 

What were the basic results?

The main findings from this study include:

• Anaesthetised mice who received a dose of triclosan showed significantly impaired cardiovascular functioning (linked to a disruption in their normal ECC response) within 10 minutes of exposure. This was dose dependant, meaning the effect was greater the larger the dose given.
• Grip strength initially decreased in mice given a dose of triclosan compared with control mice, although any changes that occurred were recovered to baseline values within 24 hours.
• Swimming activity of fish when measured as distance swum during unprovoked swimming was significantly impaired for the fish exposed to the highest dose of triclosan. Swimming activity in fish exposed to the two lower doses was not significantly different compared with controls. 
• The contraction of mouse heart muscle was further impaired after 20 minutes of exposure to triclosan.

How did the researchers interpret the results?

The researchers conclude that the evidence “is of concern to both human and environment health”.

In discussing the findings, lead researcher, Professor Isaac Pessah says: “For someone who is healthy a 10 per cent drop in heart function may not have an effect, but if you have heart disease it could make a big difference”. One of the other researchers adds that “at the very least, our findings call for a dramatic reduction in its use”.

The researchers also speculate that there may be genetic factors that make some people more vulnerable to the potentially harmful effects of triclosan. For example, some people may take longer to clear the chemical from their body. Such speculation would need to be confirmed or disproved by further research.

Conclusion

The headline that an “ingredient in hundreds of household products ‘causes heart problems’” is not supported by this animal-based study. It is often difficult to interpret the results of animal research and caution should be exercised when trying to apply the findings to humans. Results obtained in animals are not always replicated in people and more studies are needed to assess the effect of triclosan on human muscle functioning. Importantly, doses given in the study may not reflect doses contained in normal household products, so people should not be alarmed into throwing away their toiletries and lipsticks based on the findings of this early stage research alone.