FIFA raises concerns about the number of players taking food supplements and warns of the risks of failing dope tests by taking non-approved products.

Around 35 percent of players at World Cup level were regularly taking food supplements, with that figure rising to almost 50 percent at under-17 and under-20 level.

Professor Jiri Dvorak, FIFA’s Chief Medical Officer explains that many players did not seek medical advice and risked failing doping tests as a result.

"The marketing strategies of the producers of food supplements are influencing the behaviour of footballers and athletes in general," said Dvorak.

"From different surveys we know that about 60 percent of under-16 athletes in the U.S. are using nutritional supplements daily and all of them believe they will increase their performance.

"This is definitely not based upon the scientific evidence or literature, which says the opposite."

Dvorak said he was both surprised and alarmed that athletes were not seeking specialist advice.

"The same scientific studies also show that 70 percent of these young athletes do not seek adequate advice from a nutritional specialist physician, they just take it and believe it will improve their performance."

Players risk failing doping tests by taking supplements, says Dvorak.

"It is well established and proven that many of the food supplements are contaminated by prohibited substances such as anabolic steroids and other substances.

"This is, of course, very dangerous because if the athlete is subject to a doping control test and is regularly using that kind of contaminated supplement, he or she can test positive for doping.

"Therefore, FIFA has issued a serious warning to football players not to take any food supplements that have not been passed by national drug and food administrations."