A decrease in its concentration has been reported in periodontitis (28 juvenile patients; 46 subjects, 25–54 years) [37,56] in contrast to patients with both type 1 diabetes and periodontitis (10 patients) who demonstrated an increase in LPO activity which may be associated with co-occurring xerostomia and production of concentrated saliva [57,58]. Here, LPO is linked to xerostomia.