The effect of all-cause hospitalization on cognitive decline in older adults: a longitudinal study using databases of the National Health Insurance Service and the memory clinics of a self-run hospital

BACKGROUND: Cognitive decline is common in older adults and imposes a burden on public health. Especially for older adults, hospitalization can be related to decreased physical fitness. This study aimed to investigate the quantitative association between hospitalization and cognitive decline. METHODS: This was a retrospective cohort study. We performed a longitudinal study by using the combined database from the Korean National Health Insurance Service (NHIS) and memory clinic data of its self-run hospital. We identified whether hospitalized, the number of hospitalizations, and the total hospitalization days through the claim information from the NHIS database. We also identified whether hospitalization was accompanied by delirium or surgery with general anesthesia for subgroup analysis. Primary outcome was the clinical dementia rating-sum of boxes (CDR-SB) score. Secondary outcomes were mini-mental state examination (MMSE) score, clinical dementia rating (CDR) grade, and Korean-instrumental activities of daily living (KIADL) score. Multivariable mixed models were established. RESULTS: Of the 1810 participants, 1200 experienced hospitalization at least once during the observation period. The increase in CDR-SB was significantly greater in the hospitalized group (β = 1.5083, P < .001). The same results were seen in the total number of hospitalizations (β = 0.0208, P < .001) or the total hospitalization days (β = 0.0022, P < .001) increased. In the group that experienced hospitalization, cognitive decline was also significant in terms of CDR grade (β = 0.1773, P < .001), MMSE score (β = − 1.2327, P < .001), and KIADL score (β = 0.2983, P < .001). Although delirium (β = 0.2983, P < .001) and nonsurgical hospitalization (β = 0.2983, P < .001) were associated with faster cognitive decline, hospitalization without delirium and with surgery were also related to faster cognitive decline than in the no hospitalization group. CONCLUSION: Cognitive decline was quantitatively related to all-cause hospitalization in older adults. Moreover, hospitalizations without delirium and surgery were also related to cognitive decline. It is vital to prevent various conditions that need hospitalization to avoid and manage cognitive dysfunction. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-022-03701-4.