Correlates of toenail zinc in a free-living U.S. population

OBJECTIVE: No prior studies have reported on dietary correlates of toenail zinc, an easily collected biomarker of zinc status. The study aim was to identify dietary and other factors that influence toenail zinc in a healthy population, in order to understand the usefulness of this biomarker in public health studies. DESIGN: Cross-sectional comparison of toenail zinc with questionnaire measures of demographic and behavioral factors, dietary intake and supplement use. SETTING: Western Washington State, US. SUBJECTS: 106 men and 106 women, who are participants in a large cohort study, of whom 66% used multivitamins or individual supplements containing zinc. RESULTS: Increased toenail zinc concentrations were associated with increased dietary zinc intake (adjusted difference in toenail zinc between those in the highest quartile of intake vs. lowest = 11.0 ppm, p for trend = 0.03), with the association primarily among men. Borderline associations of increased toenail zinc were found with decreased vegetable intake (p=0.08) and increased body mass index (p=0.11). Supplemental zinc and intake of phytic acid, alcohol, iron (from food or supplements) did not influence toenail zinc. CONCLUSION: Toenail zinc concentrations vary with dietary zinc intake, even in a healthy population with presumably little zinc deficiency.