Multimorbidity and Functional Disability in Older Brazilians: Contrasting Patterns in Basic and Instrumental Activities, 2013–2019
Objective: To analyze the association between multimorbidity and functional disability in basic (BADL) and instrumental activities of daily living (IADL) among older Brazilian adults, and to assess changes between 2013 and 2019. Methods: A cross- sectional study was conducted using data from the 2013 and 2019 Brazilian National Health Survey, including individuals aged 60 years or older. Functional disability was assessed based on self-reported limitations in BADL and IADL, categorized dichotomously. Multimorbidity was defined as the presence of two or more chronic conditions. Analyses accounted for the complex survey design, incorporating sampling weights, strata, and primary sampling units. Prevalence ratios (PR) were estimated using Poisson regression with robust variance, adjusted for sociodemographic variables. Effect modification over time was assessed using interaction terms. Results: The sample included 33,905 individuals, representing approximately 60.8 million older adults. The prevalence of multimorbidity was 57.9% (95%CI: 57.0–58.8). Functional disability increased from 2013 to 2019 for both BADL (15.5% to 20.6%) and IADL (28.0% to 32.2%). Multimorbidity was associated with higher prevalence of disability in both outcomes, with greater magnitude for BADL (PR=2.00; 95%CI: 1.66–2.42) than for IADL (PR=1.38; 95%CI: 1.22–1.55). Functional disability was higher in 2019 regardless of multimorbidity status (BADL: PR=1.36; 95%CI: 1.15–1.63; IADL: PR=1.17; 95%CI: 1.04–1.31). No significant interaction between multimorbidity and survey year was observed. Advanced age, female sex, and lower education were associated with higher prevalence of disability, with stronger sociodemographic effects for IADL. Conclusion: Multimorbidity is a key determinant of functional disability among older adults in Brazil, with a stronger impact on basic activities. The observed increase in disability over time, independent of multimorbidity, suggests the influence of broader structural factors. Differences in the magnitude of associations between BADL and IADL indicate that social determinants play a more prominent role in instrumental limitations, while multimorbidity is more strongly associated with advanced levels of dependency.