LEP and periodontitis: Gan et al. (2018) and Thanakun, Pornprasertsuk-Damrongsri & Izumi (2017) reported that leptin levels in gingival tissue decreased as increased severity of periodontitis. In addition, Purwar et al. (2015) found that periodontitis patients had significantly lower leptin levels in their saliva than the healthy control group. Lastly, Johnson & Serio (2001) discovered that leptin levels in GCF gradually decreased with the aggravation of periodontitis inflammation.