Toenail selenium as biomarker: reproducibility over a one-year period and factors influencing reproducibility.

We assessed the reproducibility of selenium levels in toenails, comparing concentrations in two sets of specimens collected about a year apart, from 80 women (40 pre-menopausal and 40 post-menopausal) in the period October 1990 to February 1992. The women were participants in a prospective study on hormones and diet in relation to prediagnostic breast cancer (the ORDET study) conducted in northern Italy. Toenail selenium was determined by …