From the results of the present study, several factors which could influence the level of transferrin in whole saliva could be derived. Because the subjects had intact mucosal integrity, gingival inflammation might be the only source of blood contamination in saliva samples. The total gingival indices were lower in the younger females than in the older ones, but transferrin concentrations were higher in the younger females than in the older ones. There are two possible reasons for these results. Primarily, younger individuals may exhibit better transferrin synthesis compared to older ones. One previous report mentioned an age-related decrease in salivary transferrin levels [
13], which supports our results. Second, the levels of gonadal hormones and the state of menopause might affect the synthesis of transferrin, an iron-containing protein. In the proliferative phase such as the follicular and ovulatory phases, the level of transferrin in blood needs to be elevated to cope with the increased demand of the active metabolism of proliferating endometrial cells [
12]. Thus, post-menopausal women showed decreased transferrin levels in blood compared to pre-menopausal women [
9]. Interestingly, our previous study showed that the salivary concentration of transferrin during the ovulatory phase was higher than those during other phases, although there were no statistically significant differences [
10]. Therefore, the influences of age and gonadal hormones could explain the higher concentrations and secretion rates of salivary transferrin in the younger females compared to the older ones despite the lesser degree of gingival inflammation in the younger subjects. Additionally, one animal study proposed endogenous transferrin synthesis in parotid acinar cells and active transportation of transferrin to parotid acinar cells after its synthesis in hepatic cells [
11], suggesting that transferrin in whole saliva may not be solely a product of blood.
We found that the concentrations of transferrin in UWS were higher than those in SWS. The salivary concentrations of transferrin also had negative correlations with the flow rates of saliva. These results indicate that salivary flow rate affects the level of transferrin in saliva and that dilution effects occur in the stimulated condition.
The total gingival index showed no positive correlation with transferrin concentration in either UWS or SWS, but the correlation coefficient between the total gingival index and the concentration of transferrin was close to the statistical significant level only in the SWS of the younger females. The younger females may have had better chewing performance during the collection of SWS, because the younger females had more teeth than the older ones and usually younger adults had a greater biting force than older ones. Therefore, the possibility of the leakage of gingival exudates into saliva during chewing could be higher in the younger females as compared to the older ones. Tooth mobility during chewing could give rise to increased blood vessel transudation, which could be related to increases in exudates from the gingival crevice, and could ultimately increase the level of blood contamination in saliva [
15].