Tuesday May 27 2008
Brushing is key for good dental health
“Patients with a history of gum disease have been found to have a 14 per cent higher risk of developing any form of tumour”, reports The Daily Telegraph today. The findings come from an American study of 48,375 men. The researchers say that it is not clear whether gum (periodontal) disease itself causes cancer or is just a sign that a person has an immune system that makes them susceptible to cancer.
These results come from a well-designed and conducted study. The researchers give the sensible advice that “any recommendations for prevention of cancer based on these findings are premature; patients with periodontal diseases should seek care from their dentists irrespective of the effect on cancer”.
Where did the story come from?
Dr Dominique Michaud and colleagues from Imperial College London, the Harvard Schools of Medicine, Public Health and Dental Medicine and the University of Puerto Rico carried out this research. The study was funded by the US National Cancer Institute and the National Institutes of Health. It was published in the peer-reviewed medical journal: The Lancet Oncology.
What kind of scientific study was this?
This was an analysis of data collected in a prospective cohort study – the Health Professionals Follow-Up Study (HPFS). The HPFS enrolled male health professionals in the USA (mainly dentists and veterinarians) aged 40 to 75 in 1986 and followed them up until 2004. Participants filled in detailed questionnaires about their health and lifestyle, including physical activity, food intake, current smoking status and smoking history, at the start of the study and every two years after this (dietary questionnaires were sent every four years).
At the start of the study the participants were asked how many of their own teeth they still had and whether they had a history of periodontal disease with bone loss. Dental X-rays for a sample of 140 dentists and 212 non-dentists were checked to assess how reliable the answers to this question were. Follow-up questionnaires asked about any tooth loss in the previous two years. Initial and follow-up questionnaires also asked whether any diagnoses of cancer had been made (either before the study started or between questionnaires) and what type of cancer had been diagnosed. Medical records were obtained for men reporting a diagnosis of cancer. About 90% of cancer diagnoses were confirmed by medical records and the rest were confirmed by information by the participant or family member, or death certificate.
The study analysed data for 48,375 participants who had not had cancer prior to 1986 (other than non-melanoma skin cancer), and who provided information about periodontal disease. The researchers used statistical methods to look at whether men with a history of periodontal disease were more likely to develop any type of cancer, or individual types of cancer for which there were at least 100 cases. These analyses took into account factors that might contribute to periodontal disease or cancer risk, such as whether or not a person smoked, how much they smoked and how long they had smoked for, age, ethnic origin, body mass index, level of physical activity, diabetes, where they lived, height, alcohol intake, estimated vitamin D exposure and calcium, red meat, fruit and vegetable and calorie intake. The analyses were also carried out separately for people who had never smoked.
What were the results of the study?
About 16% of men reported a history of periodontal disease. Participants were followed for almost 18 years on average, and in this period 5,720 men (about 12%) developed cancer (not including non-melanoma skin cancer or non-aggressive prostate cancer). Men with a history of periodontal disease were 14% more likely to develop cancer than those with no history of periodontal disease after adjustment for other risk factors.
When they looked specific cancers, men with a history of periodontal disease had an increase in risk of cancer of the lung (36% increase), kidney (49% increase), pancreas (54% increase) and the haematological system, such as the leukaemias, (30% increase). There was no difference between the groups in other cancers, such as melanoma, stomach cancer and brain cancer.
If the researchers only looked at men who had never smoked, those with a history of periodontal disease were 21% more likely to develop cancer; this increase was largely due to a 35% increase in the risk of haematological cancers. There was no increase in the risk of lung cancer with periodontal disease in men who had never smoked.
What interpretations did the researchers draw from these results?
The researchers concluded that “periodontal disease is associated with a small, but significant, increase in overall cancer risk”, and that this increase in risk exists in men who had never smoked. They suggest that the increase in risk of lung cancer with periodontal disease is likely to be due to the effects of smoking.
Further studies are needed to confirm the increases in risk of other types of cancer and to clarify whether periodontal disease itself influences the risk of cancer, or whether it merely indicates “a susceptible immune system”.
What does the NHS Knowledge Service make of this study?
This was a well-designed and conducted study that indicates a possible link between periodontal disease and cancer. There are some limitations:
- This type of study (prospective cohort study) is the best way to investigate links between exposures that cannot be assigned randomly (in this case periodontal disease) and outcomes (in this case cancer). However, because the exposures are not assigned randomly, differences between groups other than the exposure in question can affect results. For example, in this study, men with a history of periodontal disease were more likely to be older, be current smokers or diabetic than men without a history of periodontal disease. This study took these and other potential confounding factors into account, which increases the confidence in the results. However, these adjustments may not have fully removed the effect of these factors and cannot remove the effect of unmeasured or unknown confounding factors.
- This study only included male health professionals and therefore the results may not be representative of what would be found in women or in people with differing levels of education or socioeconomic status.
- Although looking at the dental X-rays of a subset of participants indicated that self-reporting of periodontal disease was relatively reliable, some misclassification of participants may have occurred, which could have affected results.
- This study cannot tell us whether periodontal disease itself causes the increase in cancer, or whether the presence of periodontal disease indicates some other factor, such as a “susceptible immune system” that might affect cancer risk.
- The study did not look at whether men received treatment for their periodontal disease and therefore cannot say whether treatment affects cancer risk.
The authors of this study suggest that “any recommendations for prevention of cancer based on these findings are premature; patients with periodontal diseases should seek care from their dentists irrespective of the effect on cancer”.
Sir Muir Gray adds...
The scientists say, “correlation does not equal causation”; namely, the fact that A and B occur together more often than you would expect by chance does not mean that A causes B. The increased risk of gum disease and cancer are probably both due to a common cause, poverty or poor diet for example.