"No clinical trials have been published on the use of potent estrogen's like ZEN in bust-enhancing products and their use should be discouraged because of the lack of evidence of their long-term safety," Professor Ian Fentiman, a consultant breast surgeon at Guy's and St. Thomas' NHS Foundation Trust in London, said.
He said some women take the supplement to increase breast size.
"ZEN is a toxic non-steroidal mycoestrogen produced by fungi that widely contaminates agricultural products, such as crops, eliciting estrogen responses by mimicking the female sex hormones," Fentiman said in a statement. "No clinical trials have been published on the use of potent estrogens like ZEN in bust-enhancing products and their use should be discouraged because of the lack of evidence of their long-term safety."
Using ZEN in animal feed has been associated with a wide range of reproductive anomalies in livestock, including diminished fertility and infertility, reduced litter size and smaller offspring and negative effects on the reproductive organs, Fentiman said.
International studies suggest links between consumption of ZEN-fed animals and products, and early puberty in young women, he said.
"The European Union has banned using ZEN to fatten up cattle, a technique used in the United States since 1969, because of its links with precocious puberty," Fentiman said.
The study was published online ahead of print publication in the January issue of the International Journal of Clinical Practice.