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Tuesday, 2 July, 2002, 11:16 GMT 12:16 UK
Environmental 'hormones' wreck sperm
Environmental oestrogens can affect sperm
Chemicals found in the environment pose a threat to human fertility, scientists say.

Men and women may have been exposed to these chemicals from paints, pesticides and cleaning products, as well as beer, vegetables and soya.

It is likely to be female exposure which carries the most threat, say researchers.

However, they believe it may be possible to harness the same effect to make IVF techniques more effective.

It has long been suspected that increased amounts of compounds that mimic the female sex hormone oestrogen may be responsible for a reduction in sperm count and male fertility.


It is quite possible that we could be exposed to more than one of these compounds

Professor Lynn Fraser, Kings College London
Now a study by a team at King's College, London, has produced the first direct evidence of the significant impact that these chemicals have on sperm cells.

The researchers found that environmental oestrogens appeared to have a far greater impact on a sperm's ability to function than natural oestrogens.

Professor Lynn Fraser told the annual conference of the European Society of Human Reproduction and Embryology in Vienna that although the environmental oestrogens were normally 1,000 times less biologically potent than the natural oestrogens, they could be 100 times more potent in sperm.

This suggests that they might operate in a different way to female oestrogen.

Critical stage

Professor Fraser, a former chairman of ESHRE, and her team investigated how three environmental oestrogens and one natural oestrogen affected the final stage of development of sperm.

This stage, known as capacitation, is when the sperm acquires the ability to fertilise an egg.

The researchers studied this effect in mouse sperm in the test tube.

The environmental oestrogens were:

  • Genistein (G), found in soya and other legume vegetables
  • 8-prenylnaringenin (8-PN), found in hops
  • Nonylphenol (NP), found in industrial products such as synthetic cleaners, paints, herbicides and pesticides

The natural oestrogen was a form of oestradiol present in the female vagina and in the fluid containing the sperm.

All the oestrogens accelerated the development of immature sperm towards full fertility.

However, the three environmental oestrogens rendered fully mature sperm incapable of fertilising an egg.

This is because they stimulated the sperm to undergo what is known as the acrosome reaction.

This is when the cap at the head of the sperm ruptures to release enzymes which enable the sperm to penetrate the barriers surrounding the egg.

If a sperm has already undergone this reaction when it makes contact with an egg, it cannot complete the process of fertilisation.

Not necessarily bad news

Professor Fraser said: "At first sight these results might suggest that oestrogens, particularly those found in the environment, could help fertility.

"However, the responses we have seen could have negative effects over time.

"For instance, 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.

"So in natural reproduction it could be a problem, but for IVF techniques it might be a benefit."

The researchers want to investigate the effect on sperm of a combination of environmental oestrogens.

Scientists believe it is possible that small molecules found in the semen may offset the effect of environmental oestrogens, by inhibiting the acrosome reaction.

Professor Fraser said that the crucial stage for sperm was once they had entered the female reproductive tract. While they are in storage in the male testicles they are essentially in limbo, denied the space and nutrients to be active.

Routine effect

The oestrogen mimicking chemicals are found in food packaging and the coating of aluminium tins.

Professor Fraser said: "There are many, many things in the environment that contain these chemicals that we don't even think about, but just use routinely."

She said the extent of the impact on human fertility was not yet known. However, it is thought that human sperm may be even more sensitive to these chemicals than mouse sperm.

Professor Fraser said it was likely that any effect would be as a result of exposure to a number of sources.

She said: "If you ate a lot of soya and drank a lot of beer you would expect the consequences to be enhanced for these individuals, but my suspicion is that low concentrations of three of four of these chemicals is likely to have the effect."

Professor Ian Craft, director of the London Fertility Centre, said: "These findings don't surprise me at all.

"Many things in the environment probably have an adverse effect. It may be that we have to be much more aggressive about what is allowed to be used among humans."

Professor Craft said it was also important to educate young people while they were still at school about things that could have an impact on their reproductive function.

"There is nothing worse than trying to start a family at 35, and finding that your sperm count is low."

Reports from the 2002 Eshre conference in Vienna

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13 Dec 01 | Health
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