Copper's Healthy Limits Probed

Copper keeps the body healthy—especially the brain, blood and bones. But how much copper is too much?

Today's safe "upper limit" for American adults—10 milligrams a day—might need to be downsized, according to a study led by copper expert Judith R. Turnlund, a research chemist with the Agricultural Research Service.

Based at the ARS Western Human Nutrition Research Center at Davis, Calif., Turnlund is trying to fill in knowledge gaps about copper. This essential nutrient is found in such foods as liver, nuts, sunflower seeds and oysters.

In a five-month study to learn more about how the body handles excess copper, Turnlund and co-researchers showed, for the first time, that long-term intake of 7.8 milligrams of copper a day can result in a potentially unhealthy accumulation of this mineral. That's based on analyses of blood, urine and other samples from nine healthy male volunteers, age 27 to 48, who went on the high-copper regimen for approximately 4-1/2 months of the 5-1/2-month investigation.

The scientists, for example, found that the high-copper stint lowered one standard measure of the volunteers' levels of antioxidants--healthful compounds that protect cells. The regimen also interfered with some immune system defenses, reducing the volunteers' ability to fight off the Beijing strain of the flu, for instance. And, even though copper excretion increased during the high-copper regimen, the ramped-up excretion rate wasn't sufficient to remove excess copper.

Turnlund and co-researchers Joseph M. Domek, William R. Keyes and Soon K. Kim report their findings in a recent issue of the American Journal of Clinical Nutrition.

The work is of interest to nutrition researchers worldwide, as well as to companies that make vitamin-mineral supplements, and to the Food and Nutrition Board, U.S. National Academy of Sciences, which recommends daily intake levels for must-have nutrients.

ARS is the U.S. Department of Agriculture's chief in-house scientific research agency.