Triple jumper Jonathan Edwards has accused fellow athlete Mark Richardson of being "naive" for taking dietary supplements.

Richardson, the fourth and most recent athlete to test positive for the banned steroid nandrolone, blames an energy-boosting 'cocktail' he took minutes before the sample last November.

World record holder Edwards believes his British team-mate is innocent but has questioned his decision to continue taking dietary supplements despite fears there might be a link with excessive levels of nandrolone.

"With the link between supplements and athletes who have tested positive, it was naive of Mark to continue taking the products," he said.

I don't know if he had them tested independently.

"Maybe he did and felt they weren't a risk but given this link between supplements and nandrolone, it was naive of Mark to continue taking the products.

"There seems some sort of common thread between the people testing positive for nandrolone and the people taking these products."

The controversy has once again thrown the spotlight on the multi-billion pound industry of dietary sports aids.

The 400m sprinter is the the third individual t test positive who was known to use the products of Hertfordshire-based supplement manufacturer, Maximuscle.

Richardson took his normal protein supplements, acetyl glutamine and pro-max, washed down by an isotonic energy drink, Viper before the November test

All three were products of Maximuscle.

Managing director Zef Eisenberg told Radio 5 Live's Ian Payne he could categorically 'guarantee' that the Maximuscle products used by Richardson could not cause a positive nandrolone test.

He said there were only two possible explanations.

"Either the actual atheletes themselves (are lying) or there are problems with the drug testing process and the people doing it."

But doubts over the purity of dietary supplements is unlikely to diminish until the industry takes steps to regulate itself.

Only last month the govening body UK Sport published its report into nandrolone claiming supplements were the only credible cause for the increase in positive nandrolone tests (343 worldwide last year).

In Britain, 17 positive incidents were reported, compared to the four in 1998.

Dr Mike Wheeler, a member of the expert committee appointed by UK Sport to investigate the steroid, believes the supplements must be to blame.

And Dr Malcolm Brown, chief medical officer for the Great Britain team, also called for an overhaul of how the supplement industry is regulated.

Wheeler, who is attached to St Thomas' Hospital in London, said:

"The most obvious reason for all these positive tests would be from the use of dietary supplements.

"Either these are contaminated in some way or they are taking supplements or herbal remedies which they do not know contain steroids but actually do.

"There does not seem to be anything in this country which looks at these supplements and there should be."

Brown said: "People need to look at how the whole supplement industry is regulated and see if they can come up with an explanation for what's happening.

"The difficulty, of course, is that you're constrained by two things: one is the current scientific knowledge; the other is whether the list of ingredients is a true reflection of what's in the container.

"To my mind, there's something strange happening. My reaction to the increase in positive tests for nandrolone is one of dismay.

"One of the possible explanations is that there's something that athletes are taking inadvertently that's leading to a finding of these metabolites which are similar to the metabolites created if you take nandrolone."

Richardson's 400m rival, the European champion Iwan Thomas, says he has become so wary of dietary supplements he no longer takes them.

"I am now very careful in what I take especially with all the mistakes, I'd rather go without.

"It's a shame it's come to that but it's the safest way. I'm not involved with the Maximuscle range and as far as sports drinks go I stick to water.

"Anything I do take I get it checked out. You have to be a fool not to. I've no doubt Mark did too which is why this is such shocking news."

David Moorcroft, head of governing body UK Athletics which is backing Richardson, said: "The supplements athletes take are no longer regulated and don't necessarily state the exact ingredients.

"I took supplements but they were the kind of supplements you got from the high street. There was none of the American ones available then."