Salivary flow rate and the risk of cognitive impairment among Korean elders: a cross-sectional study

Background: Salivary function has been suggested to be associated with cognitive impairment. However, the effect of salivary flow rate (SFR) on cognitive impairment remains unclear. This study aimed to investigate whether SFR is associated with cognitive impairment among Korean elders. Methods: This cross-sectional study included 649 elders aged 65 and older in the Korean community-dwelling population. Cognitive impairment was assessed using the Mini-Mental Status Examination. Unstimulated SFR was measured and dichotomized. Denture status, age, sex, education level, smoking, drinking, diabetes, hypertension, and obesity were considered confounders. Multivariable logistic regression analysis was applied to assess the adjusted association. Stratified analysis by sex and denture status was performed to clarify the effect modification. Results: Participants without cognitive impairment showed a higher SFR level than those with cognitive impairment (0.81 mL/min for non-cognitive impairment versus 0.52 mL/min for cognitive impairment, p < 0.001). After controlling for confounders, participants with low SFR (< 0.3 mL/min) were more likely to have cognitive impairment by 1.5 times than participants with normal SFR (odds ratio [OR] = 1.5, confidence interval [CI] = 1.05–2.10). The association of low SFR with cognitive impairment was higher in women and dentate participants: about 10% higher in women (OR = 1.63, CI = 1.07–2.50) and about 22% higher in dentate participants (OR = 1.82, CI = 1.41–2.90). Conclusions: Salivary flow rate is independently associated with cognitive impairment among Korean elders. The association was modified in females and dentate elders. Physicians and dentists should consider low SFR and cognitive impairment as a risk factor between them in clinics.