the experimental diet was considered insufficient to maintain status and therefore deficient in copper. If plasma copper and serum ceruloplasmin concentrations did not change significantly when the experimental diet was fed, but platelet copper concentration decreased, then the experimental diet was judged to be marginally adequate in copper. A lack of change in the copper status indicators indicated that the level of copper in the experimental diet was adequate to maintain status. Because of limited data, data from men and women were combined.
Three studies were used to estimate the average requirement on the basis of copper status. These studies are summarized in Table 7-2. Serum copper and ceruloplasmin concentrations and SOD activity declined significantly in eight of 11 young men fed an experimental, depletion diet containing 388 μg/day and increased with repletion (Turnlund et al., 1997). Although these indicators decreased significantly, they did not fall to the deficient range while the deficient diet was fed for 42 days. However, it is expected that they would have fallen to the deficient range over a longer time. Other changes suggesting copper depletion were observed.
When young men were fed 790 μg/day of copper, the above mentioned indicators did not decline significantly (Turnlund et al., 1990). After a decline in copper status, two of the 11 men responded to copper repletion. Therefore, the copper requirement to maintain copper status in half of a group is more than 380 μg/day but less than 790 μg/day. On the basis of these data, a linear model was used to estimate a response curve. The model estimated that half of these men would not maintain copper status at 550 μg/day.
Serum copper and ceruloplasmin concentrations did not decline significantly when ten women were fed 570 μg/day of copper (Milne and Nielsen, 1996). Platelet copper concentration, however, declined significantly for eight of ten women fed 570 μg/day and increased with supplementation. Other indicators did not respond to depletion. Platelet cytochrome c oxidase and erythrocyte SOD activity declined but did not respond significantly to repletion. While an EAR based on the first two studies was estimated at 550 μg/day, the latter study suggests that 600 μg/day may be a marginal intake in over half of the population. Therefore, another increment was added to cover half of the population, and the EAR was set at 700 μg/day.
Factorial Analysis. Another approach for estimating the minimum copper requirement is to estimate obligatory losses of copper and calculate the amount of copper required in the diet to replace these