[Multiple medicines and incidence of functional disability among older adults according to age groups: A JAGES 2013-2019 longitudinal study].

Objectives The use of multiple medicines that increase frailty and functional disability among older adults is a significant public health concern. However, no study has analyzed whether the intake of multiple medicines increases functional disability according to age. The number and severity of diseases and frailty that are positively correlated with medicines have not been considered. In this longitudinal study, we aimed to investigate whether multiple medicines increased functional disability incidence according to age groups (65-74 and ≥75 years) after adjusting for disease status and frailty.Methods Data from the 2013 Japan Gerontological Evaluation Study (JAGES)-collected during a follow-up period of approximately six years-were used. Individuals aged ≥65 years who were activities of daily living (ADL) dependent, using an unknown number of medicines, and experiencing functional disabilities at the time of response were excluded. A total of 12,752 functionally independent older adults from 14 municipalities were included in this study. The outcome variable was whether the participants had functional disabilities. The explanatory variable was the intake of multiple medicines (reference group, no medicines; exposure group, 1-2, 3-4, or ≥5 medicines). As covariates, 12 variables were considered potential confounding factors between the intake of multiple medicines and functional disabilities. A survival analysis (Cox's proportional hazards model) was used to calculate the hazard ratio (HR), 95% confidence interval (CI), and p-value (5% significance level). After confirming the association between multiple medicines and age groups (65-74 and ≥75 years), participants were analyzed according to age groups. Multiple imputation methods were used for the missing variables.Results Among the 65-74 and ≥75 years age groups, the incidence of functional disabilities was 10.3% and 37.6%, respectively. The interaction between multiple medicines and age was significant (P < 0.05). During the follow-up period, the HR (95% CI, P-value) for functional disability incidence with the intake of multiple medicines was higher compared to that of the reference group, as follows: for 3-4 and ≥5 medicines among individuals aged 65-74 years, 1.31 (1.01-1.69, 0.042) and 1.89 (1.44-2.49, <0.001), respectively; and for ≥5 medicines among individuals aged ≥75 years, 1.43 (1.19-1.72, <0.001).Conclusion The study findings indicate that multiple medicines administered to community-dwelling older adults increase their susceptibility to functional disabilities. However, individuals aged 65-74 years with a lower disease status and frailty percentages may be attentive when using multiple medicines. Guidelines for appropriate medicine use among older adults emphasize the importance of healthcare workers in medical institutions and community pharmacies. These workers should also address the issue of multiple medicines among individuals aged 65-74 years.