Effect of taste and smell on secretion rate of salivary IgA in elderly and young persons

Two experiments were performed to determine the effect of taste and odor stimuli on secretion rate of salivary IgA in young and elderly individuals. In Experiment 1, three stimuli were applied to the tongue: 1) "flavor" drops (60% sugar, 5% cocoa powder, and 0.1 % Irish cream odor); 2) sugar (60%); and 3) water. In Experiment 2, four different foods (chicken broth, onion soup, corn, and carrots) were tested with and without monosodium glutamate (MSG). The stimuli in both experiments were delivered three times in a one hour period: t=0, t=30 minutes, t=60 minutes. The results of Experiment 1 indicated that application of sugar (taste alone) and flavor (taste and odor combined) to the tongue induced significantly higher secretion rates of sIgA than the application of water in both elderly and young subjects. In addition, flavor application produced significantly higher secretion rates of sIgA than sugar application alone. Secretion rates of sIgA in young persons were significantly higher than those in elderly persons. In Experiment 2, the increase in secretion rate of sIgA at 30 and 60 minutes for each food with MSG was greater than the same food without MSG for the elderly subjects. The increases in secretion rates of sIgA were produced by elevated salivary flow (Experiments 1 and 2) as well as increased absolute concentrations of sIgA (Experiment 1). The elevation of absolute concentrations of sIgA by chemosensory stimuli may involve neural-immune connections. The improvements in salivary flow and secretory immunity by repeated taste and smell stimulation found here have clinical potential for treatment of immune deficiencies and dry mouth which frequently occur in elderly individuals.