The Not So Clear Cut Link Between Mouthwashing and Heart Attacks

According to the Mail on Sunday, mouthwashes are a major health hazard. I’m not convinced.

The item opens by saying:

Using mouthwash is a ‘disaster’ for health, increasing the risk of heart attacks and strokes, scientists are warning.

Sounds pretty bad. Anybody reading beyond that scary first paragraph will learn that:

Professor Amrita Ahluwalia, who led the study, last night condemned the widespread use of antiseptic mouthwash.

She said: ‘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.’

More than half of British adults regularly use mouthwash, creating a market worth £180 million a year.

The study compared blood pressure levels in 19 healthy volunteers who started using Corsodyl twice daily. Their blood pressure rose by between 2 and 3.5 units [mmHg].

The story is based on this and it quickly becomes clear that the situation is a little more complicated than the Mail on Sunday makes out.

The rise in blood pressure may not seem like much considering that ideally healthy blood pressure is in the range 90/60 to 120/80 mmHg systolic/diastolic but for sufferers of high blood pressure any increase can be dangerous.

This leads to the first point about the study; the participants are healthy individuals in their twenties. It might seem reasonable to assume that what applies to this group also applies to heart patients in their fifties but it is still an assumption that cannot be categorically stated as true without tests.

The study participants measured their daytime and night-time blood pressures and the changes over the study period are shown in graph form in figure 5 of the paper. It can be seen that while a few rise steeply, the majority change very little and some actually fall. General conclusions drawn from this small sample are starting to look a little tentative. Shaky, even.

Another problem with this study is that there is no placebo arm.

When a patient is given a placebo and allowed to believe that he has actually been given a real drug, his symptoms will often improve, and sometimes dramatically so, at least in the short term. So researchers need to compare their drug against the strong effects of a placebo before they can claim that the drug is really effective.

In other words, a second group of participants should have been given a placebo mouthwash and the differences in blood pressure changes (if any) between the two groups examined before any kind of meaningful conclusions can be drawn.

This work is not a trial, just a pilot study indicating a possible avenue of research and to be fair to the authors I do not think that they see it any other way:

It is important to appreciate the limitations of this work. In this study the application of the intervention was not randomized and not placebo controlled.

Unfortunately this subtle point has been missed by the press reporting which, as is all too often the case when the press cover medical and scientific matters, consists of a tiny kernel of truth wrapped in layers of hype and glossing over of nuance. Don’t dump your mouthwash just yet.

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