The RDA for copper is set by using a coefficient of variation (CV) of 15 percent (see Chapter 1 and the discussion of adult requirements that follows) because information is not available on the standard deviation of the requirement for these age groups. The RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for copper the RDA is 130 percent of the EAR). The calculated RDA is rounded to the nearest 10 μg.

Biochemical Indicators. No single indicator was judged as sufficient for deriving an EAR for adults. Results for specific indicators vary between studies. To determine the EAR, a combination of indicators was used, including plasma copper concentration, serum ceruloplasmin concentration, erythrocyte superoxide dismutase activity (SOD), and platelet copper concentration in controlled human depletion/repletion studies using specific amounts of copper. If there were significant decreases in serum copper and ceruloplasmin concentrations and SOD activity when the experimental copper diet was fed, and if this decrease was reversed with added copper, then