Annual transitions in serum zinc status among long-term care facility residents in Japan

Background: Low serum zinc status is common in older adults living in long-term care facilities, but year-to-year transitions during routine annual health examinations remain insufficiently described. This study described adjacent annual pair-level transitions in serum zinc status and explored whether transition patterns differed according to available resident characteristics. Methods: This retrospective descriptive study used annual health examination data collected in 2021-2025 at one long-term care facility in Okinawa, Japan. Zinc deficiency was defined as serum zinc <60 μg/dL (<9.2 μmol/L). Consecutive annual measurements were paired and classified as persistent deficiency, recovery, transition to deficiency, or persistent non-deficiency. Exploratory stratified summaries were calculated according to age, sex, facility care unit, albumin, anemia, and estimated glomerular filtration rate. Results: After excluding one pair with missing baseline zinc, 361 valid consecutive annual pairs from 166 residents were analyzed. Among baseline deficient pairs, persistent deficiency was observed in 163 of 217 pairs (75.1%; 95% confidence interval, 69.0%-80.4%). Among baseline non-deficient pairs, transition to deficiency occurred in 67 of 144 pairs (46.5%; 95% confidence interval, 38.6%-54.7%). Persistent deficiency was descriptively more frequent among pairs with age ≥85 years, facility care unit 2, and albumin <3.5 g/dL. Transition to deficiency was more frequent among pairs with albumin <3.5 g/dL and anemia. Conclusion: Low serum zinc frequently persisted, and transition to deficiency was also common. Unfavorable transitions were more apparent among residents with markers of nutritional or clinical vulnerability, but facility care-unit findings were facility-specific and these findings remain descriptive and pair-level.