Wednesday, June 16, 2010

Confounding -- theme of the week

See your dentist, brush, and floss--and live longer! At least, that's what a recent study has claimed (the image is from the story). Good boys and girls who brush twice a day have a markedly lower risk of heart disease. This is the result of an epidemiological study, not a study of a particular risk factor (such as a particular pathogen that isn't brushed away in lazy, halitotic people).

A link between gum disease and risk of heart disease has been reported previously, the idea being that the bacteria that cause periodontal disease can enter the blood stream and contribute to arterial blockages, or that the inflammation that characterizes gum disease can increase risk of arterial plaque build-up.  But, this is apparently the first study to show the association of risk of heart disease with brushing. 

But, perhaps the association is not so straightforward.  As with any epidemiological correlation, the issue of confounding is certainly important, and perhaps almost impossible to rule out. Brushing and dental visits are correlated with many other factors including socioeconomic status and thus diet, exercise, and general health, factors that have been associated with risk of heart disease apart from gum disease. Those aspects not measured in a survey could lurk in the background as the real causal factors.
Study leader Professor Richard Watt, from University College London, said future studies will be needed to confirm whether the link between oral health behaviour and cardiovascular disease "is in fact causal or merely a risk marker".

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