Friday May 28 2010
It is not proven, but brushing may reduce the risk of heart attacks
“Brushing your teeth twice a day could save you from a heart attack”, the Daily Mail reported.
This news story is based on a study of how often people brushed their teeth and their risk of cardiovascular disease. People who never or rarely brushed their teeth were 70% more likely to develop cardiovascular disease than those who brushed twice a day. People with poor oral hygiene also had higher blood levels of a specific chemical marker of inflammation thought to increase risk.
This study did not establish a cause-and-effect relationship between oral health and cardiovascular disease. It is possible that people who brushed their teeth more may simply have lived healthier lives.
However, these findings are in line with other research suggesting a link between gum disease, inflammation and cardiovascular disease. While not proof of a causal relationship, this study does add further weight to the suggestion that brushing may reduce the risk of cardiovascular disease.
Where did the story come from?
The study was done by researchers from the Department of Epidemiology and Public Health, University College London. It received no specific grants from funding agencies. The study was published in the peer-reviewed British Medical Journal.
Newspaper reporting of this research was generally fair, with most stories reporting the main result accurately – that people who reported poor oral hygiene had a 70% increased risk of cardiovascular disease, compared to those who brushed their teeth twice a day. The BBC correctly reported that poor oral hygiene had not been proved as a cause of heart attacks, as this study has found only an association between the two. The Daily Mail’s headline, “Clean your teeth twice a day to keep a heart attack at bay” ignored other established risk factors for cardiovascular disease, such as obesity and smoking.
What kind of research was this?
This study was based on data from the Scottish Health Survey, a cross-sectional survey undertaken every three to five years, of a nationally representative sample of the general population in Scotland. Over the past two decades there has been increasing interest in a possible link between periodontal disease (i.e. gum disease and inflammation tissue surrounding teeth) and cardiovascular disease. Most periodontal disease is associated with inflammation. It is now thought that inflammation in the body (including mouth and gums) is also associated with damage to arteries, which can in turn lead to heart disease.
While some smaller studies have looked at the possible association between confirmed periodontal disease and cardiovascular disease, this is the first large population study to look at self-reported oral hygiene and the risk of both inflammation and heart disease. Although this type of study on its own cannot prove cause and effect, the size of the study and the fact that the participants were followed for an average of more than eight years makes the findings notable.
What did the research involve?
Researchers combined data from three of the Scottish surveys undertaken between 1995 and 2003, involving 11,869 men and women with an average age of 50 years. Survey interviewers and nurses had visited Scottish households and collected data on demographics and lifestyle. This includes risk factors for cardiovascular disease, such as smoking, physical exercise, blood pressure and medical family history. People taking part were also asked how often they visited the dentist and how often they brushed their teeth – twice, once or less than once a day.
To find out what happened to participants over time, each survey was linked to a database of hospital admissions and deaths, which was followed up until December 2007. The researchers used the database to look at the underlying causes at both the fatal and non-fatal cases of cardiovascular disease, heart attacks and admissions for bypass surgery. Blood samples were collected from 4,830 people who consented, and they were laboratory tested for two proteins called C reactive protein and fibrinogen. Both proteins are markers for inflammation.
The researchers then used established statistical techniques to analyse this body of information. They calculated the risk of heart disease and death in relation to frequency of toothbrushing, plus the association between oral hygiene and levels of inflammatory markers. Their modelling made adjustments to account for the influence of major factors that might contribute to people’s risk, such as smoking, obesity and family history. The figures were also adjusted for age, sex and socioeconomic group.
What were the basic results?
The researchers followed-up participants for an average of about eight years. Among the 11,869 people followed were 555 (4.7%) cases of cardiovascular disease, of which 170 were fatal. Most of these people were diagnosed with coronary heart disease.
Importantly, the researchers found that:
- When all other possible influences had been taken into account, people who reported poor oral hygiene (who never or rarely brushed their teeth) had a 70% greater risk of cardiovascular disease, compared with those who brushed their teeth twice a day. (Hazard ratio (HR) 1.7 (95% confidence interval [CI] 1.3 to 2.3)
- By modelling the link between toothbrushing and inflammatory markers, the researchers say that the fully adjusted model shows a reduced rate of brushing is linked to higher levels of the two markers for inflammation - C reactive protein (ß 0.04, 95% CI 0.01 to 0.08) and fibrinogen (ß 0.08,95% CI –0.01 to 0.18). This suggests a significant association.
The study also found that other known risk factors for cardiovascular disease, such as smoking and diabetes, had a stronger association than poor oral hygiene. For example, people who smoke had more than double the risk of cardiovascular disease than non-smokers.
Encouragingly, the researchers found oral hygiene to be generally good, with about 62% of participants reporting regular (at least every six months) visits to a dentist and 71% reporting good oral hygiene (brushing teeth twice a day). Participants who brushed their teeth less often than twice a day were slightly older, more likely to be men, and of lower social status. They also had a high prevalence of risk factors including smoking, physical inactivity, obesity, hypertension and diabetes.
How did the researchers interpret the results?
The researchers conclude that poor oral hygiene is associated with a higher risk level of cardiovascular disease, and also with low-grade inflammation. However, they point out that cause and effect is not yet proven. The results confirm previous findings, which have found a link between gum disease (known to be mainly caused by poor oral hygiene) and cardiovascular disease. Experimental studies, they say, are now needed to confirm whether poor oral hygiene is a cause of cardiovascular disease or a marker for other risk factors, such as smoking.
Doctors, say the researchers, should be alert to the possibility that oral hygiene causes inflammation, and patients should be told that improving oral hygiene is beneficial, regardless of any relation to heart disease.
This is the first large study to look at a possible association between self-reported toothbrushing habits and the risk of cardiovascular disease. Its findings are in line with other studies showing a link between gum disease, inflammation and heart disease, although, as the researchers point out, it cannot prove cause and effect. Its analysis used data gathered from a large, rigorously designed population survey that was linked to patient databases and followed people for a reasonably long period of time. It has also used recognised statistical methods.
However it should be noted that:
- although the study took account of other factors that might influence the development cardiovascular disease (such as smoking), it is possible that the results may have still been influenced by factors that were not measured or incompletely measured.
- Toothbrushing habits were self-reported, which could increase the chance of obtaining inaccurate data. The study did not look at clinical data on gum disease, although, as the researchers point out, previous research has shown a correlation between self-reported gum disease and clinical evaluations of the condition.
Another key point is that a 70% increased risk may sound quite large, but that it may be more useful to consider risk in terms of absolute rates, i.e. the actual numbers of people who might have been affected. Using the unadjusted figures:
- 59 people out of 538 (10.9%) who brushed their teeth less than once a day developed cardiovascular disease over about eight years
- 188 people out of 2,850 (6.6%) who brushed their teeth once a day developed cardiovascular disease over about eight years, and
- 308 people out of 8,481 (3.6%) who brushed their teeth twice a day developed cardiovascular disease over about eight years
This study did not establish a cause-and-effect relationship between oral health and cardiovascular disease. However, in theory these figures would equate to about 73 cardiovascular events in every 1,000 (10.9% minus 3.6%) being prevented by brushing teeth twice a day for eight years instead of brushing less than once a day (unadjusted). Expressed another way, only 14 people would need to do this for eight years to prevent one event (number needed to treat =14). The analysis suggests that these people would probably have other healthy habits.
It is important to remember that good oral hygiene is important to help prevent gum disease and tooth decay, regardless of its effect on cardiovascular risk. Equally, following a healthy diet and doing regular physical activity are all important, proven ways to prevent the risk of cardiovascular disease.