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).