BY LYNNE SLIM, DH, BSDH, MSDH
Easter is a fabulous time for a Georgia wedding, and my daughter, Katie, got married that particular weekend (photos/videos of the handsome groom and the blushing bride are available on my Facebook page). At the reception, a wedding guest told me she was on a gluten-free diet. Turns out it's all the rage, especially among celebrities, and I've noticed more gluten-free diet products showing up on grocery store shelves.
As a devoted evidence-based sleuth, I was wondering what gluten free really means, and I found out that there's no legal definition. In fact, the FDA just announced it will publish guidelines on labeling foods as gluten free. I'm still wondering if a gluten-free diet is safe for everyone besides individuals with celiac disease.
Tuning into an ABC online interview, I discovered there's no scientific evidence to support all the claims in Hollywood and elsewhere about adopting a gluten-free diet. There's no guarantee of weight loss. Gluten-free diets seem to have become a fad, and it reminds me of the perio/cardio link. Like some of the gluten-free diet claims, the perio/cardio link debate has also taken on a life of its own.
For those of you who haven't read the recent scientific statement by the American Heart Association (AHA) that was approved by the AHA's Science Advisory and Coordinating Committee with backing from the ADA Council on Scientific Affairs and World Heart Federation, there is no evidence that periodontal intervention prevents atherosclerotic vascular disease (ASVD) or modifies its outcomes.
Observational studies (which are very useful in addressing questions about benefits of therapy) to date support an association between periodontal disease and ASVD independent of known confounders, but this is not the same as a causative relationship. The independent association was found to be weak, and authors of the systematic review noted that many studies had low quality research designs. The authors indicated that intervention studies where a group receives periodontal treatment and is then compared to a group not receiving periodontal treatment are needed to answer the question of causation.1
Only one pilot intervention study has been published that provided periodontal intervention in a population of individuals with established CVD. The control group had usual care where subjects decided to seek oral care or not (three-fourths did not seek periodontal care). The experimental group received rigorous periodontal care on a three-month maintenance schedule. The primary outcome of the randomized intervention was the number of cardiovascular events. Both groups had similar CV events, suggesting that periodontal intervention did not prevent cardiovascular events.2
The terms confounders and causative relationship are quite a mouthful. So let me explain what this means. Let's look at an association between periodontitis and lung cancer, for example. Epidemiologists have found a statistically significant (73%) increase in the risk of dying from lung cancer for individuals with periodontitis.3 The risk was found after adjusting for variables such as age, gender, alcohol intake, socioeconomic status, and smoking habits. Variables like these can confound the results, so they need to be controlled in the study design or analysis.
Does this mean then that periodontitis causes lung cancer? Absolutely not! In reading the report in more detail, it is apparent that the association was no longer significant when the data was restricted to never-smokers. When restricted to smokers, the adjusted hazard ratio was higher by about twofold, indicating that there is a big difference between smokers and never-smokers and lung cancer risk. In other words, there are shared lifestyle risk factors for both systemic and dental diseases.
Correlation does not, and cannot imply cause and effect. Two events can occur together (such as ASVD and periodontal diseases), but one is not necessarily the cause of the other.
Here's another example, and this is an area of research that I'm particularly interested in. Many epidemiological studies showed (note that this is observational/correlational) that women on hormone replacement therapy (HRT) also had a lower incidence of heart disease (CVD). As a result, doctors proposed (and were encouraged by pharmaceutical companies in some instances) that HRT offered some protection against CVD. A closer scrutiny of the data found that the women taking HRT were more likely to be from higher socioeconomic groups with better than average diets and exercise regimens. Therefore, the use of HRT and a lower incidence in CVD were coincident with a higher standard of living.
The American Academy of Periodontology (AAP) issued a press release that showed support for the AHA statement. But the AAP press release also found the AHA-related press release to contain "overly negative and misleading information."
On the contrary, I found the AHA statement to be objective and devoid of any special interest bias. Health-care professionals are among the most common sources of bias and that includes professional associations.
This is a good reminder that our own professional association (ADHA) needs to remain vigilant in guarding against bias in association publications and continuing education courses. When you read about oral/systemic links in the future, ask an epidemiologist what correlation between two variables really means. When the AAP/ADA/ ADHA or some other group publicizes a link between periodontal disease and some systemic disease (pancreatic cancer, for example), recognize that it is important not to mislead patients or misrepresent the strength of the evidence.
The last sentence in the AHA statement warns that "...statements that imply a causative association between PD and specific ASVD events or claim that therapeutic interventions may be useful on the basis of that assumption are unwarranted."1
Is it ethical to tell patients that there is a strong relationship between CVD and periodontal diseases and that periodontal treatments may reduce negative effects? Well, would you tell your very best friend to go on a gluten-free diet to lose weight? RDH
References
1. http://circ.ahajournals.org/content/early/2012/04/18/CIR.0b013e31825719f3
2. Offenbacher S, Beck JD, Moss K, Mendoza L, Paquette DW, Barrow DA, Couper DJ, Stewart DD, Falkner KL, Graham SP, Grossi S, Gunsolley JC, Madden T, Maupome G, Trevisan M, Van Dyke TE, Genco RJ. Results from the Periodontitis and Vascular Events (PAVE) study: a pilot multicentered, randomized, controlled trial to study effects of periodontal therapy in a secondary prevention model of cardiovascular disease. J Periodontol. 2009;80: 190–201.
3. Meyer MS, Kaumudi J, Giovannucci, E, Michaud DS. A review of the relationship between tooth loss, periodontal disease and cancer. Cancer Causes Control 2008 Nov; 19(9): 895-907. E pub 2008 May 14.
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