Increased dietary intake of antioxidants has previously been linked with better lung function but this is the first research to highlight a potentially negative impact from copper.
Writing in this month's issue of the European Journal of Clinical Nutrition (vol 59, pp1043-1048), a team from the University of Nottingham said: "The association between higher serum copper and lower forced expiratory volume requires further study in view of the ubiquitous exposure to this mineral."
The researchers used a random subsample of 479 participants, aged 18-65 years old, from a larger cross-sectional observational study.
They measured forced expiratory volume in one second, an indicator of how good the lungs are. They also measured blood plasma levels of copper, vitamin C, vitamin E and serum selenium.
They found that those participants with higher levels of copper were less able to exhale as much oxygen in the desired time.
"Copper is a transitory metal. It can have prooxidant effects," Andrew Fogarty, senior author, told NutraIngredients.com.
Much of the intake of copper in the diet is through water, particularly if people live in older houses with copper pipes, he added.
Furthermore, recent research out of the US suggests that the body cannot excrete all of the copper when taken in amounts higher than that found in the diet. Excess copper could be associated with reduced immune function and lower antioxidant status, according to a team from the Agricultural Research Service.
In contrast, the antioxidant nutrients vitamin C and selenium could reduce the damage done by oxidation in the lungs.
However Fogarty added that while the findings supported the need for further work on antioxidants, a large, double-blind, randomized trial last year showed no benefit from antioxidant vitamins on the lung health of participants.