COLOGNE, Germany (AP) _ A leading German doping expert's research strengthens the link between food supplements and the rash of positive tests for nandrolone which has engulfed top sports stars such as Linford Christie and Dutch soccer player Edgar Davids.
Prof. William Schanzer said Friday his Institute of Biochemistry in Cologne had conducted tests on volunteers giving them supposedly clean nutritional supplements. A few hours later, their urine test was positive.
``It shows the possibility exists the athletes unknowingly took impure food supplements leading to their positive tests,'' Schanzer said.
There were 343 positive tests in 1999 in all sports for nandrolone, which builds muscles and strengthens bones, with many of the athletes claiming they hadn't knowingly used the drug.
Schanzer said his tests may explain why the wave of positive tests for the drug continue despite the negative headlines generated by cases like that of former 100 meter Olympic champion Linford Christie, American shot-putter C.J. Hunter and Jamaican sprinter Merlene Ottey.
Just last month, top Dutch soccer players Frank de Boer of FC Barcelona and Davids of Juventus Turin failed tests for nandrolone and were suspended.
Schanzer cautioned that athletes will still have to prove their positive test was generated by hormones in supplements which are billed as being clean if they are to be cleared of doping charges.
``In many of the cases, the athlete is going to have to exactly document his intake of food supplements,'' Schanzer said.
Schanzer's institute tested nutritional supplements claiming to contain ``no forbidden substances,'' giving them to volunteers, who had urine tests before and after ingesting the products.
In three of the supplements, the test subjects showed up positive within three or four hours. One contained guarana, which is commonly available in health food shops as a herbal stimulant.
Schanzer didn't say how many volunteers were involved in the tests, saying that his institute plans to publish its research more extensively at a later date.
The long list of other sports figures who have failed drug tests for nandrolone include tennis player Petr Korda, French World Cup player Christophe Dugarry and former 5,000 Olympic champion Dieter Baumann of Germany.
Schanzer pointed out that on some athletes already have managed to document that a positive test for nandrolone came from impure supplements. Last summer, German second division soccer player Manuel Cornelius was cleared in this way.