Suggested lower cutoffs of serum zinc concentrations for assessing zinc status: reanalysis of the second National Health and Nutrition Examination Survey data (1976-1980)

Background: The risk of zinc deficiency in populations can be estimated by comparing serum zinc data with statistically defined lower cutoffs derived from a presumably healthy population. Serum zinc data are available from a large sample of the US population assessed during the second National Health and Nutrition Examination Survey (NHANES II). Although the original analysis of these data considered fasting status-and the time of day of blood sampling, it did not account for potentially confounding variables that may affect the serum zinc concentration, such as age, sex, and health status. Objective: The objective was to describe variations in serum zinc concentration by age, sex, and other characteristics and to recommend lower cutoffs for presumably healthy persons. Design: Serum zinc data from NHANES II were analyzed by using analysis of variance and covariance models to identify and describe variables significantly associated with serum zinc concentration; 2.5th percentile curves were produced and used to establish age- and sex-based lower cutoffs. Results: Age and sex were significant confounders of serum zinc concentration, so separate lower cutoffs were derived for children and adolescent and adult males and females. Other minor confounding variables were identified. Tentative lower cutoffs for pregnancy and oral contraceptive use were also derived. Conclusions: The interpretation of population serum zinc data with the use of lower cutoffs should account for the age and sex of the subjects, pregnancy and oral contraceptive use, and fasting status and time of day of blood collection.