Scientists found that toxic chemicals can damage sperm, which then pass altered genes onto babies. In experiments on rats Matthew Anway of the University of Idaho found that some garden chemicals caused problems such as damaged and overgrown prostates, infertility and kidney problems, all of which were present up to four generations later.
Cynthia Daniels, of Rutgers University in New York, an expert in the relation between a father and child's health, said: "If I was a young man I would not drink beer, I would not be smoking when I'm trying to conceive a child."
It is well known that a mother's health is critically important in the resulting health of her baby, but there is now a growing body of evidence from both animal and human studies that paternal exposure to toxins can also adversely effect the development of a foetus, and that this can be passed down the generations.
Daniels, who led a seminar at the American Association for the Advancement of Science annual meeting in Boston, said: "Historically it has been assumed that exposures to the male will not affect his ability to pass defects on to children."
Scientists at the seminar listed problems including pregnancy loss, low birth weight, increased birth defects and childhood cancers in children fathered by men who were exposed to toxins, from pesticides and prescription drugs to wartime chemicals. Vietnam veterans exposed to agent orange, for example, have been shown to have children with increased rates of spina bifida.
"Men who drink excessive amounts of alcohol produce higher rates of sperm with abnormalities," said Daniels. "There are many potential sources of harm to foetal health that remain unexamined. When 60% of birth defects are of unknown origin, why are we not examining one obvious potential source of harm?"
In a study presented at the same seminar, Anway described how his team exposed pregnant rats to the fungicide vinclozolin and found that the sperm of males had been affected. Anway explained the reason behind the changes as epigenetic, where chemicals in the environment can switch genes in the body on and off. Epigenetic changes are not usually passed to children unless they happen in germ cells such as sperm.
Daniels' advice to young couples trying for a baby is to think about both parents' exposure to chemicals. "If you minimise your exposure to toxic substances then you might minimise your risks of reproductive harm."
The good news for men is that sperm is produced continuously in a 74-day cycle, so the body does clean itself over time.
Alok Jha, science correspondent The Guardian, Tuesday February 19 2008