SALT LAKE CITY -- U.S. athletes were warned by the U.S. Anti-Doping Agency to avoid dietary supplements offered at training centers before the Salt Lake City Olympics.

The International Olympic Committee's medical commission found unlisted, banned performance enhancers in 40 of 200 dietary supplements it tested this year. The IOC warned athletes last month to avoid dietary supplements because of what it called lax quality control and labeling.

The official warnings appear to be at odds with the sponsorship deals the Salt Lake and U.S. Olympic committees cut with Utah-based Pharmanex, a maker of supplements. A subsidiary of Nu Skin, Pharmanex is the exclusive supplement supplier to the U.S. Skiing and Snowboarding Association, SLOC and the USOC.

The USOC stocks Pharmanex vitamin, mineral and "phytonutrient" products at athlete training centers.

SLOC President Mitt Romney has said Pharmanex and Nu Skin quality control measures are adequate and that he has no qualms endorsing their products.

Terry Madden, director of the U.S. Anti-Doping Agency, said Friday that Olympic drug testing labs can detect banned substances in much smaller traces than Food and Drug Administration purity tests. Some manufacturers, he said, use the same production line to make vitamins that they use to make IOC-banned performance boosters.

"We're working behind the scenes quietly to get our government to move on this issue," Madden said.