Longitudinal Association Between Oral Status and Cognitive Decline Using Fixed-effects Analysis.

BACKGROUND: Although the feasibility of randomized trials for investigating the long-term association between oral health and cognitive decline is low, deriving causal inferences from observational data is challenging. We aimed to investigate the association between poor oral status and subjective cognitive complaints (SCC) using fixed-effects model to eliminate the confounding effect of unobserved time-invariant factors. METHODS: We used data from Japan Gerontological Evaluation Study (JAGES) which was conducted in 2010, 2013, and 2016. ß regression coefficients and 95% confidence intervals [CIs] were calculated using fixed-effects models to determine the effect of deteriorating oral status on developing SCC. Onset of SCC was evaluated using the Kihon Checklist-Cognitive function score. Four oral status variables were used: awareness of swallowing difficulty, decline in masticatory function, dry mouth, and number of teeth. RESULTS: We included 13,594 participants (55.8% women) without SCC at baseline. The mean age was 72.4 (standard deviation [SD], 5.1) years for men and 72.4 (SD, 4.9) years for women. Within the 6-year follow-up, 26.6% of men and 24.9% of women developed SCC. The probability of developing SCC was significantly higher when participants acquired swallowing difficulty (ß = 0.088; 95% CI, 0.065-0.111 for men and ß = 0.077; 95% CI, 0.057-0.097 for women), decline in masticatory function (ß = 0.039; 95% CI, 0.021-0.057 for men and ß = 0.030; 95% CI, 0.013-0.046 for women), dry mouth (ß = 0.026; 95% CI, 0.005-0.048 for men and ß = 0.064; 95% CI, 0.045-0.083 for women), and tooth loss (ß = 0.043; 95% CI, 0.001-0.085 for men and ß = 0.058; 95% CI, 0.015-0.102 for women). CONCLUSION: The findings suggest that good oral health needs to be maintained to prevent the development of SCC, which increases the risk for future dementia.

Cohort Study on Laryngeal Cough Reflex, Respiratory Disease, and Death: A Mediation Analysis.

OBJECTIVE: To estimate quantitatively whether the presence of cough associated with dysphagia (laryngeal cough reflex) increased mortality through respiratory disease among community-dwelling older Japanese. DESIGN: A 6-year follow-up prospective cohort study (from 2010 to 2017). SETTING: Thirteen municipalities in Japan. PARTICIPANTS: Community-dwelling individuals aged 65 years or older (N = 32,682). MEASURES: The baseline survey was conducted through self-reported questionnaire. Exposure was experience of laryngeal cough reflex while drinking. The outcome was all-cause mortality. All covariates were selected from demographic, socioeconomic variables, baseline health and functional status, smoking, alcohol drinking, number of remaining teeth, and stroke. The mediator variable was respiratory disease. Cox proportional hazards regression was used to estimate hazard ratios (HRs) for mortality. Parametric mediation analysis was conducted to estimate the effect of laryngeal cough reflex on the mean residual time to death mediated through respiratory disease. RESULTS: Among the 32,682 participants (mean age = 74.1 years, standard deviation = 5.9 years), 5550 (17.0%) experienced laryngeal cough reflex at baseline. A total of 4037 deaths occurred. Crude mortality rates of the participants with or without laryngeal cough reflex were 16.3% and 11.6%, respectively. After adjusting for covariates, laryngeal cough reflex [HR = 1.10; 95% confidence interval (CI) = 1.02 to 1.19] and respiratory disease (HR = 1.80; 95% CI = 1.62 to 2.00) were associated with mortality. The mediation analysis showed that respiratory disease significantly (P < .001) and partially mediated the association between laryngeal cough reflex, an indicator of 1 or more conditions such as chronic aspiration and mortality. CONCLUSIONS/IMPLICATIONS: Laryngeal cough reflex was a prevalent condition, and it was associated with all-cause mortality in community-dwelling older Japanese individuals. Clinicians could contribute to reduce mortality risk by addressing swallowing function problems using their interprofessional collaboration team (speech-language pathologist, dentist, rehabilitation doctor, otolaryngologist, respiratory physician, and gerontologist).

Impact of oral self-care on incident functional disability in elderly Japanese: the Ohsaki Cohort 2006 study.

OBJECTIVES: To assess whether oral self-care (tooth brushing, regular dental visits and use of dentures) affects incident functional disability in elderly individuals with tooth loss. DESIGN: A 5.7-year prospective cohort study. SETTING: Ohsaki City, Japan. PARTICIPANTS: 12 370 community-dwelling individuals aged 65 years and older. PRIMARY OUTCOME MEASURES: Incident functional disability (new long-term care insurance certification). RESULTS: The 5.7-year incidence rate of disability was 18.8%. In comparison with participants who had ≥20 teeth, the HRs (95% CIs) for incident functional disability among participants who had 10-19 and 0-9 teeth were 1.15 (1.01-1.30) and 1.20 (1.07-1.34), respectively (p trend<0.05). However, the corresponding values for those who brushed their teeth ≥2 times per day were not significantly higher in the '10-19 teeth' and '0-9 teeth' groups (HRs (95% CI) 1.05 (0.91-1.21) for participants with 10-19 teeth, and 1.09 (0.96-1.23) for participants with 0-9 teeth), although HRs for those who brushed their teeth <2 times per day were significantly higher (HRs (95% CI) 1.32 (1.12-1.55) for participants with 10-19 teeth, and 1.33 (1.17-1.51) for participants with 0-9 teeth). Such a negating association was not observed for other forms of oral self-care. CONCLUSIONS: Tooth brushing may partially negate the increased risk of incident functional disability associated with having fewer remaining teeth.