Title: FW: [globalnews] Lead may cause mystery male infertility
(For Hugh...)
Lead may cause mystery male infertility
12:56 06 February 03
NewScientist.com news service
Environmental lead may be to blame for some cases of unexplained male
infertility, say US researchers. Their findings have prompted them to warn
that environmental exposure limits for lead need re-evaluation
The study, involving 140 couples participating in IVF treatment, showed that
higher lead levels in the men's semen was associated with low fertilisation
rates, the first conclusive evidence of such a link. Importantly, none of
the men were in occupations likely to result in high lead exposure.
"I'm very excited about our findings. We were not expecting a big role for
lead - none of the men showed outward lead toxicity," says Susan Benoff, at
the North Shore-Long Island Jewish Research Institute in Manhasset, New
York. The work, and results still to be published, are not just applicable
to couples undergoing IVF, she says. "It's true in the general public."
Sperm function tests showed that high lead levels in the semen samples
correlated with a reduced ability of the sperm to bind to the egg, and also
to then penetrate and fertilise the egg. A causal link between lead levels
and reduced fertility was supported by additional experiments, in which
researchers exposed sperm from nine fertile men to increasing doses of lead.
The study is "an interesting new development", says Richard Sharpe, of the
MRC Reproductive Sciences Unit at the University of Edinburgh, Scotland. He
said it would move infertility concerns about lead and other heavy metals
"into the spotlight".
Binding to the egg
Benoff and colleagues from other US institutions examined the effects of
metal ions, including lead, zinc and cadmium, on the sperm function. The
semen samples were taken from the partners of women undergoing their first
IVF cycle. The men completed lifestyle questionnaires, including details
about their occupation, to try to rule out confounding factors.
The researchers found wide variation in lead levels in the men's seminal
plasma, with high levels correlating with low fertilisation rates.
Statistically, the lead level variation could account for a fifth of the
variation in fertility.
When levels were high, there were fewer receptors on the head of the sperm
that recognise and bind to sugars on the egg. High levels also hampered the
ability of the sperm to penetrate the egg in a reaction called the acrosome
reaction. Self-destructive "spontaneous" acrosome reactions, which occur
before the sperm even reaches the egg, were also more common in lead rich
samples.
Competing metals
Benoff told New Scientist this could be because lead displaces calcium,
which is essential for the processes of sperm function and spermatogenesis.
She says the fact that none of the men were at risk of excessive
occupational exposure shows environmental exposure limits for lead need
re-evaluation. In the US, recommended maximum exposure limits are between
100 to 150 milligrams per cubic metre of air.
Lead stays in the body for much longer than most metals, adds Benoff, with a
half-life of 11 years in bone. She said one possible treatment for men with
high lead levels might be to take supplements of zinc - popular in the 1970s
- which competes with lead.
Journal reference: Human Reproduction (vol 18, p 374)
Shaoni Bhattacharya
