Longitudinal association between toenail zinc levels and the incidence of diabetes among American young adults: The CARDIA Trace Element Study

Data on primary prevention of zinc status and diabetes risk are sparse and inconsistent. Of note, the previous studies measured either dietary zinc intake with questionnaire or zinc status in serum or hair. Toenail zinc levels are reliable biomarkers of a relatively long-term exposure. A total of 3,960 American young adults, aged 20–32 years, free of diabetes at baseline in 1987 when toenail clippings were collected, were examined for incident diabetes through 2010. Toenail zinc levels were measured with an inductively-coupled-plasma mass spectroscopy method. Incident diabetes cases were identified by fasting or non-fasting plasma glucose levels, oral glucose tolerance tests, hemoglobin A1C levels, and/or antidiabetic medications. During the 23-year follow-up, 418 incident diabetes occurred. After adjusted for age, sex, ethnicity, study center, body mass index, education, smoking status, alcohol consumption, physical activity, family history of diabetes, homeostasis model assessment of insulin resistance, and other dietary and non-dietary potential confounders, the hazard ratio of incident diabetes comparing the highest to the lowest quartile of toenail zinc levels was 1.21 (95% CI: 0.90–1.63; P trend = 0.20). Findings from this study do not support the hypothesis that zinc status is inversely and longitudinally associated with the incidence of diabetes in American young adults.