Copper absorption and retention in young men at three levels of dietary copper by use of the stable isotope 65Cu

Eleven young men were confined to a metabolic research unit for 90 d to determine the effect of the level of dietary copper on absorption and retention. Cu absorption was determined by feeding the stable isotope 65Cu. Absorption and retention averaged 36.3 +/- 1.3% and 0.17 mg/d, respectively, with an adequate-Cu diet (1.68 mg/d). Absorption averaged 55.6 +/- 0.9% and retention averaged -0.316 mg/d for 6 d and 0.093 mg/d for the next 36 d of a low-Cu diet (0.785 mg/d). Absorption averaged 12.4 +/- 0.9% with a high-Cu diet (7.53 mg/d) and retention was strongly positive at first, decreasing linearly with time. The study demonstrated that Cu absorption is strongly dependent on dietary Cu level and that Cu balance can be achieved by most young men from a diet of 0.8 mg Cu/d. These results suggest that current dietary Cu recommendations may be higher than necessary. The apparent regulation of Cu absorption and endogenous losses would tend to protect humans from Cu deficiency and toxicity.