RETN and rheumatoid arthritis: Since serum levels of resistin are elevated in obesity and in systemic diseases such as diabetes mellitus and rheumatoid arthritis, and are also increased in the GCF and serum of patients with periodontitis, it can be assumed that resistin increases periodontal inflammation, thereby increasing the risk of periodontal disease or impairment of periodontal healing [14, 19, 20].