WARNING: SOYA MAY BE MAKING MEN INFERTILE
DAILY MAIL, TUESDAY, APRIL 15, 2003
By James Chapman, Science Correspondent
The increasing amount of soya being eaten in Britain could be
putting the fertility of a generation of men at risk, according to an
alarming new study.
Researchers believe that pregnant or breast-feeding women who eat
soya and soya-based products, such as tofu, could be endangering their
babies because these foods contain chemicals that mimic the female
hormone, oestrogen. Experts fear that exposure in the womb, or through
breast milk, could lead to reproductive abnormalities in boys. They are
also concerned about the possible impact of soya-based infant foods.
The scientists, based at Johns Hopkins University in Baltimore,
Maryland, tested the effects of genistein €“ the key
chemical found in soya beans €“ on pregnant rats.
Alarmingly, they found that their male offspring developed abnormal
reproductive organs and experienced sexual dysfunction as adults.
The researchers are calling for more research to be carried out
urgently to see if the increasingly popular soya and soya-based foods
affect human reproductive development in the same way. The warning is
supported by the Scientific Advisory Committee On Nutrition, which
advises the British Government. It said last month there is
€œclear evidence€ that soya-based formula milk could
damage children€™s sexual development and fertility as
adults. Large amounts of genistein are found in some baby formula milks
and supplements taken by women, as an alternative to hormone
replacement therapy.
The average sperm count of a European male has dropped by a quarter
over the past 25 years and about 27,000 British couples seek treatment
for infertility problems each year, an increase of 55 per cent in five
years. As many as one in six couples is thought to have problems
conceiving.
In the new study, published in the latest issue of the Journal Of
Urology, pregnant female rats were randomly assigned a genistein-free
diet or one containing the chemical. Male offspring were exposed to
genistein indirectly through maternal consumption during pregnancy and
after birth through breast milk. When the offspring who were exposed to
genistein matured, researchers found the males had smaller testes and a
larger prostate gland and lower testosterone levels compared to
unexposed rats. Although their sperm counts were normal, exposed adult
males had lower testosterone levels and were also less likely to mate
successfully.
€˜The effects of genistein continued long after the rats
were exposed€™, said Dr Amy Wisniewski, who led the
research at the Johns Hopkins Childrens Centre. €˜This
leads us to believe that exposure to this plant-derived oestrogen
during reproductive development can have long-term detrimental effects
in males€™.
Dr Sabra Klein, another member of the research team, added:
€˜Genistein may act as an oestrogen or an anti-androgen,
blocking the function of endogenous androgens €“ the sex
hormones necessary for males to develop a normal reproductive
system.
€˜Ultimately, it appears this leads to the reproductive
abnormalities and sexual dysfunction we saw in the exposed rats.
€˜However, additional research is needed to determine if
this is the case€™.
Whether the long-term effects of genistein on reproductive
development are caused by exposure during gestation, lactation or both
also requires further investigation, the scientists said.
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