Does brushing your teeth lower cardiovascular disease?

Yes, says a new article in the British Medical Journal:

Toothbrushing is associated with cardiovascular disease, even after adjustment for age, sex, socioeconomic group, smoking, visits to dentist, BMI, family history of cardiovascular disease, hypertension, and diagnosis of diabetes.

…participants who brushed their teeth less often had a 70% increased risk of a cardiovascular disease event in fully adjusted models.

The idea is that inflamed gums lead to certain chemicals or clot risks.

In the past five days I’ve seen this study reported in five newspapers, half a dozen radio news shows, and several blogs. These researchers know how to use a PR firm.

Sounds convincing. What could be wrong there?

OH WAIT. MAYBE PEOPLE WHO BRUSH THEIR TEETH TWICE A DAY GENERALLY TAKE BETTER CARE OF THEMSELVES AND WATCH WHAT THEY EAT.

I’m consistently blown away by what passes for causal analysis in medical journals.

Here’s a cruel and simplified guide to prevailing opinion and practice:

Medical research: Correlation never implies causation.

Epidemiological research: My correlation implies causation, because I controlled for socioeconomic status.

Economics: Confused and conflicted, but sometimes correlation implies causation. If you can find a cool instrumental variable we’ll surely publish you.

I side with the economists on this one.

As punishment, I suggest the people who ran (and published) the BMJ study be made to eat nothing but Krispy Kremes while brushing their teeth four times a day.

P.S. If interested, my causal inference syllabus is here.