Soya-based foods may harm male fertility, say scientists: Study
links ingredient to lower sperm count
Chemical mimics female sex hormone
Ian Sample, science correspondent, The Guardian, Thursday
July 24 2008
Men who eat soya-based foods may be harming their fertility, doctors
said yesterday, after a study found a link between soya-rich diets and
lower sperm counts.
The study showed men who consumed more than two portions of
soya-based foods a week had, on average, 41m fewer sperm per millilitre
of semen than men who had never eaten soya products.
The apparent fall in sperm count is unlikely to make healthy men
infertile, but some experts said it could have a significant impact on
those already with lower than average sperm counts. A sperm count of
between 80m and 120m per ml is regarded as normal, while men who
produce fewer than 20m sperm per ml are regarded as clinically
subfertile.
The study, by Jorge Chavarro at Harvard school of public health in
Boston, builds on previous research in animals and on human tissues
that has suggested certain ingredients in soya could harm sperm
production.
Male fertility has been in decline in the west for several decades,
with about 20% of young Europeans having a low sperm count, while
levels of soya have risen steadily in the western diet since the 1940s
because it is a cheap source of protein. Soya-based products are now
found in two-thirds of manufactured food including biscuits, sweets,
pasta and bread, according to the Institute of Food Research in
Norwich.
In the biggest human study into the effects of soya on fertility,
Chavarro and colleagues at Massachusetts General hospital recruited 99
men who had visited a fertility clinic between 2000 and 2006. The men
were asked to fill out a questionnaire which asked them about the
amounts of 15 different soya foods they had eaten over the previous
three months. The researchers then put the men into four groups
according to the levels of chemicals called isoflavones in their diets.
Isoflavones are ingredients in soya products that mimic the female sex
hormone, oestrogen. Each man then provided a sperm sample for
testing.
Chavarro found that men who consumed at least half a portion of soya
food a day had the lowest sperm counts.
"Our findings suggest that the greater the soya food intake is, the
lower the sperm concentration, compared with men who never consume soya
food," said Chavarro, whose study appears in the journal Human
Reproduction.
Richard Sharpe, of the Medical Research Council's human reproductive
sciences unit, said: "The take-home message could be that if you've got
an already low sperm count ... soya foods are probably not a good idea
for you, as they could have a real impact on your fertility by further
lowering your sperm count."
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