June 11, 2012

expert reaction to study of dental plaque and cancer mortality

An observational study in the journal BMJ Open linked persistent dental plaque with an increased risk of dying early from cancer.

Dr Paul Pharoah, Reader in Cancer Epidemiology at the University of Cambridge, said:

“The data suggest that increasing levels of plaque are associated with a higher all cause mortality. There is no comparison of cancer-specific mortality.

“The authors quote an odds ratio for mortality associated with dental plaque after adjustment for some covariates. The odds ratio of 1.79 is hard to interpret, but as plaque was measured on a continuous scale it probably means a 70 percent increase in mortality for every increase in the plaque measurement of 1 unit. It is unclear what a one unit increase in plaque means, but as the average plaque index was about 0.7 a one unit increase has no real meaning.

“Over the 24 years of follow-up the average death rate was 2 per thousand per year. For the 2.5 percent of the population with a plaque index about 1 higher than average (1.7 compared to 0.7) the average death rate would be about 3 per thousand per year. That means that a small proportion of the population with the worst level of plaque are at a slightly increased risk of dying.

“This association may not be causal. Although some factors were controlled for there are very likely to be other factors, such as diet and obesity that would be associated with both plaque and mortality.

“The study found that only sex, age and plaque were associated with mortality. This questions the validity of the whole study as factors such as smoking and socio-economic status should generate a measureable effect on all cause mortality.”

‘The association of dental plaque with cancer mortality in Sweden. A longitudinal study’ by Birgitta Soder et al., published in BMJ Open on Monday 11 June.