Persistent Zinc Deficiency Among Residents of a Long-Term Care Facility: A Five-Year Longitudinal Study

Background Zinc deficiency is common in older adults, particularly among residents of long-term care facilities, yet its longitudinal course in this setting remains insufficiently described. Methods We conducted a five-year longitudinal observational study using routine health examination data collected between 2021 and 2025 in a long-term care facility in Okinawa, Japan. Serum zinc concentrations were measured annually at the same clinical laboratory. Residents with at least two zinc measurements were included. Zinc deficiency was defined as a serum zinc concentration below 60 μg/dL, and zinc status patterns were classified as persistent low zinc, incident zinc deficiency, recovered zinc status, or stable normal zinc status. Results Among 267 residents with repeated measurements, persistent zinc deficiency was the predominant pattern and was observed in 184 residents (68.9%). Recovery from zinc deficiency occurred in 14 residents (5.2%), whereas 18 residents (6.7%) developed incident zinc deficiency and 51 residents (19.1%) remained zinc-sufficient throughout follow-up. The prevalence of zinc deficiency changed little between baseline and follow-up, from 198 residents (74.2%) to 202 residents (75.7%), and baseline and follow-up serum zinc concentrations showed a moderate positive correlation. Conclusions Low serum zinc concentrations were common and often remained low over time in this cohort of frail long-term care residents. These findings suggest sustained biological or nutritional vulnerability in long-term care settings. However, because serum zinc may be influenced by inflammation, chronic disease, and supplementation, persistent low values should be interpreted cautiously and in conjunction with clinical context and, where possible, additional biomarkers.