Feb. 6, 2003 -- Lead may be behind up to a fifth of unexplained male infertility cases, according to a new study. For the first time, researchers say they've found evidence that even low-level lead exposure from household contaminants may damage sperm and contribute to male infertility.
In light of these findings, researchers say fertility specialists should consider lead measurements when evaluating male partners from couples with unexplained infertility. They also recommend public health and safety officials reevaluate current environmental exposure limits for lead.
The study, published in the February issue of Human Reproduction, examined lead levels and sperm function in semen collected from the male partners of 140 women undergoing in vitro fertilization (IVF) treatment for the first time. Researchers found lead levels varied widely among the men and there was a significant association between high lead levels and low fertilization rates, which accounted for about a fifth of the variation in successful IVF rates.
Researchers Susan Benoff, MD, director of the Fertility Research laboratories at the North Shore-Long Island Jewish Research Institute in Manhasset, New York, and colleagues say laboratory tests showed that high lead levels interfered with both the ability of the sperm to bind to the egg and to fertilize the egg.
To fertilize an egg, sperm must first successfully bind to the egg and then induce a reaction that allows it to pass through the egg's coating for fertilization. But the study found that sperm that came from semen with higher lead levels were unable to bind to the egg properly or stimulate the reaction necessary to pass through the egg's coating.
To confirm the association between high lead levels and low fertilization rates, researchers exposed healthy sperm to increasing doses of lead to see what would happen, and they got the same results. In other experiments they found that elevated levels of lead in the testes of rats lead to the death of sperm.
Researchers say the were surprised to find such high lead levels in the semen of the men studied because none of them were engaged in occupations likely to expose them to high levels of lead. Some high lead levels were associated with smoking or alcohol use, but there were unexplained high levels in other men who didn't drink or smoke.
Other possible explanations for the finding may be a lack of exercise, low calcium, or high-fat diet, which can cause lead levels to increase and accumulate over time. Genetic differences in how the body responds to lead exposure may also play a role, because some men with high lead levels in their semen were able to fertilize successfully.
Common household sources of lead exposure include lead-based paints, piping, and plumbing fixtures as well as contaminated soil.
SOURCE: Human Reproduction, Feb. 6, 2003.