The relationship between dehydration and parotid salivary gland function in young and older healthy adults

Saliva is essential for the maintenance of oral health. The primary constituent of saliva is water and, traditionally, decreased body water homeostasis has been linked with salivary dysfunction. This is consistent with the greater prevalence of dehydration and salivary gland dysfunction among the elderly. However, this association between dehydration and salivary dysfunction has never been tested using objective criteria. The purpose of this study was to determine the effect of body dehydration upon parotid salivary flow rates in young and older healthy adults.

Twelve young (20-40 years) and 12 older (60-80 years) healthy subjects abstained from food and beverage intake for 24 h (dehydration) and then underwent intravenous rehydration to replace all lost weight. Unstimulated and stimulated parotid salivary flow rates, weight, hematocrit, hemoglobin, serum sodium, plasma protein, creatinine, serum, and urine osmolality values were assessed at baseline, 24 h, and 1 h after the completion of rehydration.

All subjects experienced a significant decrease in weight and increased levels of hematocrit, hemoglobin, plasma protein, and creatinine during dehydration with few age-related differences. Intravenous fluid replacement increased weight and decreased hematocrit, hemoglobin, plasma protein, and creatinine back to baseline values, demonstrating that subjects were metabolically rehydrated. Unstimulated (young and older, p = .0001) and stimulated (young, p > .05; older, p = .03) parotid flow rates decreased during the 24-h dehydration period, yet did not completely return (young and older unstimulated, p < .001; young and older stimulated, p > .05) to baseline values after rehydration.

These findings suggest that body dehydration is associated with decreased parotid salivary gland flow rates, and that these changes are generally age-independent in healthy adults. Furthermore, although subjects were metabolically rehydrated, unstimulated salivary flow rates remained significantly lower than baseline levels.