A positive association was repeatedly demonstrated between prevalent periodontal disease and obesity across multiple studies from around the world. The meta-analysis of the systematically identified results from 57 independent study populations suggested an approximate one-third increase in the prevalence odds of obesity among subjects with periodontal disease, a greater mean clinical AL among obese individuals, a higher BMI among subjects with periodontal disease, and a slight but not statistically significant linear increase in the odds of periodontal disease with increasing BMI. In total, these findings are highly unlikely due to chance and persist over studies using a multitude of measurement strategies for assessing these two health conditions.
The summary measure of association (sOR) reported here was less strong in magnitude than those reported between periodontal disease and adverse pregnancy outcomes106
or cardiovascular events.107
However, based on a subset of included studies, there appears to be stronger obesity–periodontitis association in women, non-smokers, and younger individuals than in the general adult population. Although smoking is a well-studied predisposing factor for periodontitis,108,109
smoking and BMI share a complex relationship,110
which can appear to be inverse in certain populations.111,112
For older individuals, tooth loss and impaired masticatory function might be a path through which advanced periodontal disease could impact energy balance and nutrition.113
Studies that linked overweight or obesity to tooth loss reported positive,114–116
and equivocal results118,119
and are complicated by an association between tooth loss and underweight status.113
Though widespread, the use of meta-analysis has been controversial,120–122
and any result must be interpreted cautiously. Confounding and heterogeneity more often influence observational studies than clinical trials, which is a limitation in pooling results. Although oral diseases are sometimes presented as if separate entities from systemic conditions, shared risk factors, such as behavior and genetic predisposition, frequently precede the manifestation of disease. Incomplete accounting of confounding factors has made drawing unequivocal conclusions about periodontal-systemic disease connections an elusive goal.123–125
Neither the sMD reflecting pooled differences in clinical AL across obese and non-obese groups nor the sMD based on pooled differences in BMI across periodontal disease patients and healthy controls was adjusted to account for confounding and, thus, likely overstates any causal difference across groups. However, the sOR based solely on adjusted results did not differ greatly from that comprised of all studies and maintained a statistically significant positive association (). However, for studies that presented both adjusted and crude results, the adjusted sOR was lower and remained potentially biased by unmeasured factors such as physical inactivity,37,126
The preferential publication of statistically significant positive results, or those deemed important, might theoretically bias the results of any meta-analysis.129,130
Indeed, we observed a handful of results in the literature with low precision but strongly positive findings (). However, attempts to account for small study effects, either by exclusion or trim-and-fill techniques, did not greatly alter the sOR estimate.
The design of nearly all included studies was cross-sectional, making it impossible to determine the temporal relationship between diseased states. Whether one condition stands as a risk factor for another, or whether a measured covariable might represent a confounder or mediator on a causal pathway, could not be distinguished. Recent work73
showed that individuals with periodontal pockets at baseline were more likely to develop components of MetS, including obesity, 4 years later. Two other prospective studies131,132
appeared during the literature search but were excluded because of a lack of peer review. Hopefully, these efforts preclude the arrival of more high-quality prospective studies that are necessary to validate the proposed causal links between obesity and periodontitis.
To our knowledge, the present analysis is the first on this topic that was systematic and quantitative in approach. We estimated the magnitude of the periodontal disease–obesity association with weighting by study precision and explored differences across subgroups of similar studies. A systematic search allowed for the inclusion of studies for which the association between obesity and periodontal disease was not a primary focus but from which an effect estimate could be abstracted and greatly widened the evidence base for this review.
This review did not cover investigations into the putative causal mechanisms that underlie the observed association between periodontal disease and obesity. However, Bullon et al.15
proposed a bidirectional relationship between MetS and periodontitis mediated by circulating cytokines and oxidative stress. Alternately, Hujoel et al.133
argued that a failure to account for correlations among health-promoting behaviors could create strong but spurious associations between oral factors and systemic conditions, such as seen between obesity and a lack of flossing. Although the cross-sectional association between obesity and periodontal disease is consistent with a causal framework, deciphering the directionality of this relationship cannot be accomplished based on prevalence studies alone.