Environmental lead may be to blame for some cases of unexplained male infertility, United States researchers say.
Their study was published in the February issue of British medical journal, Human Reproduction.
Lead remains in high levels in the environment and is known to reduce fertility in animal models, but a direct link between lead exposures and human infertility had not been established before.
The study was conducted by Susan Benoff at the North Shore-Long Island Jewish Research Institute in New York and colleagues from other US institutions.
Involving 140 couples participating in IVF (in vitro fertilization) treatment, it showed that higher lead levels in the men's semen was associated with low fertilization rates, the first conclusive evidence of such a link.
The researchers 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 were required to complete 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 fertilization rates.
When lead levels were high, there were fewer receptors on the head of the sperm that recognize and bind to sugars on the egg. High lead levels also hampered the ability of the sperm to penetrate the egg in a reaction called the acrosome reaction.
The scientists suggested that this could be because lead displaces calcium, which is essential for the processes of sperm function and spermatogenesis.
None of the men were in occupations likely to result in high lead exposure. It showed environmental exposure limits for lead need re-evaluation.
(eastday.com February 9, 2003)
