Copper absorption from foods labelled intrinsically and extrinsically with Cu-65 stable isotope

Objective: To determine copper absorption from copper containing foods labelled either intrinsically or extrinsically with a highly enriched Cu-65 stable isotope label. Design: A longitudinal cross-over study. Setting: The study was conducted at the Institute of Food Research, Human Nutrition Unit, Norwich, UK. Subjects: Subjects were recruited locally via advertisements placed around the Norwich Research Park. A total of 10 volunteers (nine female, one male) took part in the study, but not all volunteers completed each of the test meals. Interventions: A highly enriched Cu-65 stable isotope label was administered to volunteers in the form of a reference dose or in breakfast test meals consisting of red wine, soya beans, mushrooms or sunflower seeds. Faecal monitoring and mass spectrometry techniques were used to estimate the relative quantities of copper absorbed from the different test meals. Results: True copper absorption from the reference dose (54%) was similar to extrinsically labelled red wine (49%) and intrinsically labelled sunflower seeds (52%), but significantly higher than extrinsically labelled mushrooms (35%), intrinsically (29%) and extrinsically (15%) labelled soya beans and extrinsically labelled sunflower seed (32%) test meals. Conclusions: The use of Cu-65 extrinsic labels in copper absorption studies requires validation according to the food being examined; intrinsic and extrinsic labelling produced significantly different results for sunflower seeds.