Polydoctoring and health outcomes among the very old population with multimorbidity: a retrospective cohort study in Japan.

To assess the relationship between polydoctoring and patient outcomes, we conducted a retrospective cohort study using a Japanese population-based dataset from April 2014 to December 2022. Overall, 2,338,965 patients aged 75-89 years with at least two chronic conditions were included. Polydoctoring was assessed by the number of regularly visited facilities (RVFs). The primary outcome was all-cause mortality, with secondary outcomes being all-cause hospitalizations, hospitalizations for ambulatory care-sensitive conditions (ACSCs), and outpatient costs. During the study period, 14.5% of participants died, 52.2% were hospitalized, and 12.5% experienced ACSC-related hospitalizations. Patients without RVFs had the highest mortality risk (HR: 3.23, 95% CI: 3.14-3.33), while those with ≥ 5 RVFs had the lowest (HR: 0.67, 95% CI: 0.62-0.73). ACSC-related hospitalizations were U-shaped, with increased risk at ≥ 5 RVFs (HR: 1.13, 95% CI: 1.06-1.22). Outpatient costs increased 3.21 times for ≥ 5 RVFs compared to 1 RVF. Polydoctoring was associated with reduced mortality but higher hospitalization rates and costs, with an optimal RVF range of 2-3 which minimized ACSC-related admissions. These findings emphasize the need for strategies that balance the benefits and costs of polydoctoring to support sustainable healthcare through improved care coordination and resource management for aging populations.