The impact of spousal health status on the risk of decline in activities of daily living (ADL) in older adults: evidence from a 2018–2021 cohort study in Shanghai, China

In Chinese society, the family plays a crucial role in caring for older adults, with informal caregiving by spouses being the preferred approach. However, longitudinal evidence on functional interdependence within older couples and its relationship with different caregiving configurations remains limited. This study aimed to examine the association between changes in activities of daily living (ADL) among older spouses, identify factors associated with each partner’s functional change, and explore differences in ADL change across baseline care configurations. This longitudinal cohort study included 6,850 older adults comprising 3,425 married couples who were followed in Shanghai, China, from 2018 to 2021. ADL change was calculated as the final available score minus the baseline score. Reciprocal multivariable linear regression models were used to examine associations between partners’ ADL changes and selected demographic, socioeconomic, caregiving, and residential-environment characteristics. Differences in mean spousal ADL change across care subgroups were examined using Welch’s one-way analysis of variance. Changes in partners’ ADL scores were positively associated in reciprocal models (β = 0.164, p < 0.001). In the model of spousal ADL change, compared with participants without baseline ADL disability, mild disability was associated with a 1.789-point lower spousal ADL change score (95% CI − 1.998 to − 1.580, p < 0.001), and moderate or severe disability was associated with a 4.044-point lower score (95% CI − 4.483 to − 3.605, p < 0.001). Formal care hours were positively associated with spousal ADL change (β = 0.004, 95% CI 0.003 to 0.005, p < 0.001), whereas the association with informal care hours was not statistically significant (β = −0.003, 95% CI − 0.005 to 0.000, p = 0.074). Mean spousal ADL change varied descriptively across care groups, but the overall between-group difference was not statistically significant (Welch F(4, 51.34) = 1.97, p = 0.114). Functional changes were correlated within married older couples, and baseline disability severity and selected care-related characteristics were associated with spousal ADL change. Differences across care configurations were not statistically significant. These findings support a dyadic approach to assessing functional health in older couples but do not establish causal effects of caregiving or identify a superior care configuration.