Ward-Level Variation and Clinical Correlates of Low Serum Zinc Among Long-Term Care Facility Residents: A Five-Year Retrospective Cohort Study.
Kudeken Norifumi N
Zinc deficiency is common among older adults and may contribute to frailty, immune dysfunction, and nutritional vulnerability. However, longitudinal evidence describing zinc status among residents of long-term care facilities (LTCFs) remains limited. This retrospective cohort study analyzed annual health examination data from 141 residents registered at baseline in 2021 at a long-term care facility in Okinawa, Japan, with follow-up data available through 2025. Serum zinc concentrations were measured yearly at the same clinical laboratory using consistent analytical methods. Demographic and laboratory variables including age, sex, albumin, hemoglobin, estimated glomerular filtration rate, long-term care insurance care-need level, enteral tube feeding, and polaprezinc use were collected. Serum zinc levels remained persistently low during the 5-year observation period. Among residents in Wards 1 and 2, 38.2% of measurements showed serum zinc levels below 50 μg/dL and 78.4% were below 60 μg/dL. Zinc levels differed across wards, reflecting differences in resident case-mix and care needs. Ward 2 included residents with higher care needs, including five residents with care-need level 4; all 10 residents receiving enteral tube feeding were also in Ward 2, whereas Ward 3 included residents with lower care needs and support-level care. Among residents in Wards 1 and 2, mean zinc levels did not significantly differ across years (ANOVA, p = 0.39), indicating persistent low zinc levels without significant improvement. In multivariable analyses, serum albumin levels were strongly associated with zinc levels. Persistent zinc deficiency was therefore common among LTCF residents during the study period. These findings suggest that routine assessment of zinc status may help identify nutritional vulnerability among institutionalized older adults.