According to the authors the findings for OPG and RANKL/OPG were expected; however, the finding of lower levels for RANKL in smokers was unexpected and suggests RANKL can be affected by factors other than smoking (e.g., sex, age, gingival disease, rheumatoid arthritis, multiple myeloma, and diabetes) [25]. Here, TNFSF11 is linked to rheumatoid arthritis.