Association of weight loss and decreased food intake with mortality in the oldest population: People in their 80s versus those aged ≥90 years

• Japan is one of the world's leading nations in longevity with a super-aging society • Therefore, maintaining and improving nursing home care quality is important • Mortality in residents aged ≥90 years was associated with WL and DFI • Only DFI was associated with an increased mortality risk in patients in their 80s This study investigated the relationship between weight loss (WL), decreased food intake (DFI), and mortality among nursing home residents in their 80s and those aged ≥90 years. A retrospective cohort study was conducted with 296 residents aged ≥80 years (138 in their 80s and 158 aged ≥90 years) from five nursing homes in Japan. All had care need levels ≥3 and had been admitted for at least 3 months. Data from electronic care records (2016–2020) were analyzed. WL was categorized with cutoffs at 3%, 5%, and 10%, and DFI was assessed with a 10% cutoff, measured over 90 days post-admission. Cox proportional hazard models evaluated the associations between WL, DFI, and mortality for both age groups. For residents aged ≥90 years, WL was significantly associated with mortality at all cutoffs: 3% WL (hazard ratio [HR] 2.22), 5% WL (HR 3.22), and 10% WL (HR 8.86). No significant association was found between WL and mortality in their 80s (3% WL: HR 1.97; 5% WL: HR 1.27; 10% WL: HR 1.86). DFI was significantly associated with increased mortality risk in both age groups. WL of 3% or more and DFI of 10% or more within the first 90 days were linked to higher mortality risk in residents aged ≥90 years. For those in their 80s, only DFI was associated with increased mortality risk. Monitoring WL and DFI is crucial for assessing mortality risk, especially in the oldest residents.