Mouthwash hogwash?

The Herald (from the Daily Mail again, sigh) has a story about deadly mouthwash

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

In a small experimental study, 19 people who spent two weeks using a type of mouthwash not recommended for long-term use ended up with slightly higher blood pressure, by 2-3.5mmHg (or ‘mmgh’ as the story says). This was an uncontrolled study and everyone had the with-mouthwash and without-mouthwash experimental periods in the same order, so it could just have been a problem of experimental design, but it’s quite plausible that it’s true, and similar results have been found in the past.

What’s a bit surprising is that the story regards this as entirely a bad thing. The hypothesised reasons for the blood pressure difference is that the mouthwash kills bacteria in the mouth that make nitrite. You probably have heard of nitrite in previous Herald or Daily Mail stories.  It’s usually  described as a preservative for cured meats and is anathematised for its presumed potential to cause cancer. Even the introduction in the mouthwash research paper mentions that nitrite has traditionally been regarded as harmful and doesn’t give any of the recent evidence to the contrary.

There is also a widespread belief, though based on relatively weak evidence, that gum and mouth infections increase the risk of heart disease. Since the type of mouthwash being studied is recommended only for treatment, not for long-term use, it might easily decrease rather than increase the risk of heart disease if used as recommended.

It’s not obvious whether the benefits of mouthwash for chronic disease would outweigh the disadvantages, even if the research had studied the sorts of mouthwash (such as Listerine) intended for daily use. It is clear that the context, even context present in the abstract of the open-access research paper, is being ignored.