Meta-Analysis of Salivary Flow Rates in Young and Older Adults

ObjectivesTo determine whether salivary flow decreases as a function of aging. DesignMeta-analysis. SettingLiterature review. ParticipantsIndividuals aged 18 and older reported to be free of major systemic disease. MeasurementsRelevant studies were identified through a literature search of several databases, from their inception to June 2013. Studies were included if saliva had been collected on at least one occasion in subjects aged 18 and older and if the data were presented in a manner that enabled comparisons of younger and older participants. Differences in salivary flow rates between age groups were calculated for each salivary source and condition and reported as standardized mean differences (SMDs), standard errors (SEs) and 95% confidence intervals (CIs). The results were pooled using a random effects model. A separate analysis examining medication use was also conducted. ResultsForty-seven studies were included. Whole (SMD = 0.551, SE = 0.056, 95% CI = 0.423-0.678, P < .001) and submandibular and sublingual (SMSL) (SMD = 0.582, SE = 0.123, 95% CI = 0.341-0.823, P < .001) salivary flow rates were reduced significantly in older participants and in unstimulated and stimulated conditions. In contrast, parotid and minor gland salivary flow rates were not significantly reduced with increasing age. Additionally, unstimulated and stimulated SMSL, and unstimulated whole salivary flow rates were significantly lower in older adults, regardless of medication usage. ConclusionThe aging process is associated with reduced salivary flow in a salivary-gland-specific manner; this reduction in salivary flow cannot be explained on the basis of medications. These findings have important clinical implications for maintaining optimal oral health in older adults.