Avocado, vegetables and contaminated red meat have all been cleared, leaving health supplements as the main suspect in the great nandrolone mystery which is threatening to tarnish Linford Christie as a drugs cheat.

That was the conclusion of a committee set up by UK Sport to investigate the disturbing number of nandrolone doping cases that have occurred in the past two years.

The committee ruled out some of the more bizarre reasons advanced by athletes for testing positive and pointed the finger of blame at some of the many health supplements which have recently flooded the market. "Some dietary supplements contain compounds similar to nandrolone or its metabolic precursors, which produce the same metabolites as does nandrolone," said Professor Vivian James of the University of London, who led the review.

It remains unclear whether athletes have been taking these supplements knowing they contain a banned substance or have been misled by unscrupulous companies.

"Users of inadequately or incorrectly labelled products are at risk of unknowingly ingesting a banned substance," said James, calling for a "high level of awareness" within the sports community about such supplements.

The report vigorously defends the practices of the International Olympic Committee's accredited laboratory at Kings College, London.

The spate of nandrolone cases has taken the authorities by surprise because, among anabolic steroids, it is virtually prehistoric. A synthetic version of testosterone, it helps the body to increase muscle mass.

David Moorcroft, the chief executive of UK Athletics, hopes that the report will help persuade the IAAF to acquit Christie and Walker.

"The inference is that the potential danger is poorly labelled supplements, which is a major concern," he said. "The advice is, don't take supplements."