Chlorhexidine mouthwash alters the gut microbiome

Health and Wellness 16. jun 2024 2 min Professor Mattias Carlström Written by Kristian Sjøgren

People’s oral bacteria are linked with their gut bacteria, and killing oral bacteria with chlorhexidine mouthwash thus alters the composition of the gut microbiome. A researcher says that gut bacteria that are normally associated with an increased risk of developing type 2 diabetes and obesity disappear, but this is not necessarily a sign of improved health.

Many people have antibacterial mouthwash on a bathroom shelf next to their toothbrush. Advertising for these products promises better oral hygiene and protection against plaque, caries and gingivitis.

This sounds very enticing, but new research shows the down side of trying to control oral bacteria.

The research shows that the composition of gut microbiota of people who use chlorhexidine mouthwash is considerably less diverse, with diversity being inextricably linked to good health.

The researchers behind the study therefore recommend that chlorhexidine mouthwash not be put in the bathroom next to the toothbrush but rather in the trash bin.

“We found changes in the gut microbiome that reduce the absorption of important nutrients. Chlorhexidine mouthwash establishes a microbial imbalance that must be unhealthy in the long term,” explains a researcher behind the study, Mattias Carlström, Professor, Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

The research has been published in Scientific Reports.

Fewer viable oral bacteria

The new study is not the first to show that using chlorhexidine mouthwash to improve oral hygiene alters the gut microbiome.

Previous studies have shown that using chlorhexidine mouthwash can lead to high blood pressure and can disturb how well the body regulates blood glucose (homeostasis).

Mattias Carlström has previously published studies showing that using chlorhexidine mouthwash strongly affects some oral bacteria that are considered healthy.

Mattias Carlström and colleagues are especially interested in the nitric oxide balance in the body.

Nitric oxide plays an important role in minimising the oxidative stress that can lead to the development of such diseases as cardiovascular and neurodegenerative diseases. Nitric oxide in the blood also helps to relax the muscles around the blood vessels and thereby reduce blood pressure.

The body produces its own nitric oxide, but bacteria also produce nitric oxide by converting nitrate to nitrite.

Some bacteria in the oral cavity are equipped with nitrate reductase, which can convert diet-derived nitrate into nitrite. We can then convert this nitrite into nitric oxide.

“We cannot convert nitrate into nitrite ourselves. No mammal can do that, and we therefore depend on the bacteria. But using chlorhexidine mouthwash eliminates all these bacteria and thus this alternative source of nitric oxide, which is important for good health,” says Mattias Carlström.

Mouthwash given to mice

The researchers investigated how using chlorhexidine mouthwash affects other important gut bacteria.

They therefore gave mice chlorhexidine mouthwash and examined faecal samples to determine how this changed the gut microbiome.

The mice were fed a Western diet with a high fat and sugar content.

“Dysbiosis in the mouth or the intestines is well known to lead to the development of high blood pressure, cardiovascular disease, kidney disease, type 2 diabetes and obesity, but the influence of oral bacteria on the gut is less well researched,” explains Mattias Carlström.

Lost weight – but not healthy

The results revealed that using chlorhexidine mouthwash has major effects, reducing both the quantity and diversity of gut bacteria, which is generally not a sign of good health.

The researchers also found that these mice appeared to immediately have a healthier metabolic profile. They lost weight, reduced body fat, improved homeostasis between insulin and glucose and had less fat accumulation in the liver despite not reducing calorie intake.

All of this may sound very healthy, but triglycerides and proteins in the gut were also increased, indicating that the chlorhexidine-induced change in the composition of gut bacteria reduces nutrient absorption.

“The scary thing is that chlorhexidine can reduce nutrient absorption across the gut. This may well reduce fat accumulation in the short term but is unhealthy in the long term,” says Mattias Carlström.

He says that the discovery is only one part of the equation; the second part is understanding how using chlorhexidine mouthwash ends up affecting the composition of gut bacteria that are associated with adverse health outcomes.

“We do not yet know about this link, but our results nevertheless clearly indicate that prolonged use of chlorhexidine mouthwash should be discouraged if it is not necessary to treat some type of oral disease,” concludes Mattias Carlström.

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