Chemicals mimicking female hormones contained in substances as humdrum as beer, paint and tofu can affect human fertility, British researchers have discovered.
Scientists found that even though the environmental chemicals oestrogens are a thousand times less biologically potent than the oestrogen found naturally in a woman's body, they have an unexpectedly powerful effect on sperm, potentially causing them to "burn out" long before they reach the egg.
Sperm are thought to be most vulnerable to the chemicals after they have left the man and entered the woman.
Researchers from King's College, led by Lynn Fraser, looked at what happened to mouse sperm when it was treated with oestrogen as naturally present in women, and with three environmental oestrogens, two found in plants and one in industrial products.
They found that all the oestrogens got the sperm moving - the process known as capacitation - but that the three environmental oestrogens were also likely to trigger premature production by the sperm of the chemical key which allows it to enter the egg for conception.
Making sperm more frisky might help fertilisation in lab conditions, such as in IVF treatment for infertile couples. But for couples trying to conceive the natural way, it could be a problem.
"The fact that the oestrogens stimulated uncapacitated cells in an unregulated manner could mean that the sperm peak too soon, before they have found an egg to fertilise," Professor Fraser told the European Society of Human Reproduction and Embryology meeting in Vienna yesterday.
The scientists looked at three environmental oestrogens - genistein, found in soya and other legume vegetables; 8-prenylnaringenin (8-PN), found in hops; and nonylphenol (NP), found in industrial products such as synthetic cleaners, paints, herbicides and pesticides.
Even though two of the oestrogens are natural, and people have been drinking beer for thousands of years, the proliferation of synthetic oestrogens such as nonylphenol means the overall amount and variety we are exposed to is likely to be higher than 40 years ago.
"We want to know if the responses are even greater when we use more than one of these environmental oestrogens. My suspicion is that combinations of environmental oestrogens would still have a significant effect," said Prof Fraser.
Soya has a much higher con centration of genistein than other legumes, and people who consume a lot of soya products will consume a relatively high amount of oestrogen. Synthetic oestrogens are found in pesticides, in packaging, plastics, shampoos and cosmetics. "Our study is the first to provide indirect and direct evidence that natural and environmental oestrogens significantly affect sperm fertilising ability," said Prof Fraser.
Now she wants to see the research extended to humans. The big unknown is whether natural chemicals in a woman can cope with the array of environmental oestrogens she might have ingested.
If it turned out that women's reproductive systems were able to keep the sperm from succumbing to the negative effect of the environmental oestrogens, they might actually have a good effect, by making sluggish sperm more mobile.
