The data available to set an EAR are limited for men and women, as well as the number of levels of dietary copper in the depletion/ repletion studies. Thus, a CV of 15 percent is used because information is not available on the standard deviation of the requirement for pregnant women. The RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of individuals in the group (therefore, for copper the RDA is 130 percent of the EAR). The calculated RDA is rounded to the nearest 100 μg.

The EAR for lactation is determined on the basis of the copper intake necessary to replace copper secreted daily in human milk plus the EAR for adolescent girls and adult women. The average amount of copper that is secreted in human milk and must be absorbed is approximately 200 μg/day. Copper bioavailability for the adult consuming the EAR for copper is about 65 to 70 percent; therefore an additional 300 μg/day of copper must be consumed to replace the copper secreted in human milk, assuming that there is no increase in the efficiency of copper absorption during lactation. Animal data suggest that maternal absorption of copper increases during lactation and could provide for about half of the added increment, but data are not available for humans on copper absorption during lactation.