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Another inadvertent way to kill off good bacteria. From the January 27, 2014 Medical Daily:

Antiseptic Mouthwash Raises Heart Attack Risk, Blood Pressure: Chlorhexidine Kills Off 'Good' Bacteria That Helps Blood Vessels Relax

Antiseptic mouthwash is commonly used to quickly refresh and clean the mouth after brushing your teeth in the morning, after eating, and before going to bed. According to a recent study published in the journal Free Radical Biology and Medicine, using a mouthwash twice daily — such as Corsodyl — may increase blood pressure up to 3.5 millimeters of mercury (mmHg), raising your heart attack risk.

Now a team of researchers at Queen Mary University of London believe using antiseptic mouthwash daily could increase the odds of HBP (high blood pressure) due to a chemical that kills the “good” bacteria responsible for helping the blood vessels relax.

Professor Amrita Ahluwalia, lead author of the study, and her team of researchers, observed the effects of a chlorhexidine-based antiseptic mouthwash — Corsodyl — by measuring the blood pressure of a small cohort of healthy participants during a two-week period. Chlorhexidine is an antiseptic that treats gingivitis and others problems of the mouth and gums. A total of 19 participants were recruited for the study during an initial seven-day control period followed by a seven-day treatment period with the antiseptic mouthwash. 

The findings revealed Cordosyl use retracts the oral bacterial conversion from nitrate to nitrate which reduces the plasma nitrate levels that are associated with increases in blood pressure. The mouthwash led the participants’ blood pressure to rise between 2 to 3.5 mmHg, with a noticeable effect found within one day of using the mouthwash twice.

The study authors believe killing off “good” oral bacteria plays a vital role in determining the plasma nitrate levels, and the bodily control of blood pressure. “Killing off all these bugs each day is a disaster, when small rises in blood pressure have significant impact on morbidity and mortality from heart disease and stroke,” said Ahluwalia, the Daily Mail reported. However, she adds, “We are not telling people to stop using antiseptic mouthwashes if they have a gum or tooth infection — but we would ask why anyone else would want to.”

The findings of the study do not apply to all mouthwashes because not all mouthwashes contain the chemical chlorhexidine, such as the popular Listerine. The study authors caution other mouthwashes could still produce the same effects as Corsodyl by damaging the mouth’s healthy bacteria.