Four studies were conducted in smokers and nonsmokers with periodontitis and found smokers had significantly lower levels of salivary osteocalcin (OC) (P < 0.001) [88]; a lower median serum level of OPG (P = 0.0006) [88]; higher levels of prostaglandin E-2, lactoferrin, albumin, aspartate aminotransferase, lactate dehydrogenase, and alkaline phosphatase [96]. This evidence concerns the gene TNFRSF11B and periodontitis.