Relationship between non-alcoholic fatty liver disease and periodontal disease: a review and study protocol on the effect of periodontal treatment on non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that is prevalent worldwide. Non-alcoholic steatohepatitis (NASH) is an advanced form of NAFLD and carries the risk of progression from hepatic inflammation and fibrosis to cirrhosis and hepatocellular carcinoma. Pathological mechanisms of NAFLD have been proposed, such as the two-hit hypothesis and the multiple parallel hit hypothesis. Periodontal disease is a chronic infectious disease of the tissues surrounding the teeth that result in tooth loss. Several reports have indicated that periodontal infection is related to NAFLD. NAFLD and periodontal disease are chronic inflammatory conditions that are known as ‘silent diseases’. Therefore, both conditions need to be detected early and treated under collaborative medical and dental care in order to prevent progression to NASH. For this purpose, further investigations in humans on the relationship between NAFLD and periodontal disease and on the effect of periodontal treatment on NAFLD are necessary. In this paper, studies on the relationship between NAFLD and periodontal disease are reviewed and a clinical study investigating the effect of periodontal treatment on NAFLD is introduced. Introduction Several studies in recent years have reported on the relationship between systemic disease and periodontal disease [1,2]. It has been reported that chronic periodontal disease is related to conditions, such as diabetes mellitus (DM), atherosclerosis and heart disease [3-6]. We have previously reported that infection with periodontal pathogens is associated with the progression of atherosclerosis [7]. Fatty liver disease, which is one of the causes of atherosclerosis [8,9], includes non-alcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (AFLD) [10]. NAFLD (in which fat accumulates in the liver without a history of drinking or immune system disease) has gained attention worldwide. NAFLD includes simple steatosis and nonalcoholic steatohepatitis (NASH), which is characterized by a chronic and progressive liver pathology [11]. The prevalence of NAFLD in the American general adult population is 10%-40% and that of NASH is approximately 2%-5% [12]. Recent animal and human investigations have indicated that NAFLD/NASH is related to periodontal disease [13,14]. As patients with liver or periodontal disease have few subjective and early symptoms, the diseases are often severe when they are discovered at medical institutions. [15,16]. Therefore, early detection and treatment under collaborative medical and dental care is important to prevent progression to NASH, which may then develop into cirrhosis or liver cancer. Further investigations in humans on the relationship between NAFLD and periodontal disease and on the effect of periodontal treatment on NAFLD are desired. This paper reviews studies on NAFLD and periodontal *Correspondence to: Dr. Chieko Kudo, DDS, PhD, Lecturer, Division of Periodontology, Department of Oral Function and Restoration, Graduate School of Dentistry, Kanagawa Dental University, 82 Inaoka-cho, Yokosuka, Kanagawa 238-8580, Japan, Tel: +81-46-822-8855; E-mail: [email protected]