Serum Zinc Concentrations and Dietary Zinc Adequacy in Children and Adolescents with Chronic Conditions: An Exploratory Secondary Analysis

Background/Objectives: This secondary analysis evaluated the discordance between dietary adequacy and serum zinc levels in children and adolescents with chronic diseases, exploring the nutritional and biochemical traits of patients within an intermediate serum zinc range. Methods: Serum zinc was measured via atomic absorption spectrophotometry, and dietary tracking was conducted using a prospective 72 h food record. Subgroups were classified using Japanese Society of Clinical Nutrition thresholds (<60, 60–<80, and ≥80 μg/dL), treating the 60–<80 μg/dL band strictly as an operational, exploratory classification rather than a validated pediatric diagnostic standard. Results: Among the 90 participants, 31% fell into the 60–<80 μg/dL intermediate serum range and 61% exhibited inadequate dietary intake. Status discordance was frequent: 41% presented with inadequate dietary intake despite maintaining normal serum levels (≥80 μg/dL), whereas 11% had intermediate serum levels despite achieving adequate dietary intake. There was no significant association between serum zinc concentration and dietary zinc intake. Operationally classified intermediate-range participants demonstrated several nutritional and biochemical differences, notably showing higher intakes of vitamins B6, D, and E, elevated triglycerides, ESR, and IgG3, alongside lower hemoglobin. Conclusions: Dietary adequacy and serum zinc levels are frequently discordant, reinforcing that these metrics serve as complementary rather than interchangeable indicators of zinc status. The distinct profiles observed within the operational 60–<80 μg/dL category provide candidate relationships that warrant future targeted investigation.