Smoking and male fertility breakthrough

Mothers who smoke while they are pregnant or breast feeding may be damaging the future fertility of their sons, according to breakthrough findings from University of Newcastle researchers.

The study, published online in Human Reproduction, one of the world's leading reproductive medicine journals, is the first comprehensive animal model to show how smoking can affect the fertility of male offspring.

Lead researcher, Professor Eileen McLaughlin, Co-Director of the University of Newcastle's Priority Research Centre in Chemical Biology, said it was already known that smoking in pregnancy harmed the baby in the womb, with babies often born small and vulnerable to disease.

Researchers investigated damage to the DNA of cells that were involved in the process of producing sperm, sperm counts, the shape of the sperm and how well they swam. They also investigated the ability of the male offspring to produce their own offspring.

"Our results show that male offspring of 'smoking' mothers have fewer sperm, which swim poorly, are abnormally shaped and fail to bind to eggs during in vitro fertilisation studies," Professor McLaughlin said.

"Consequently, when they reach adulthood they are sub fertile or infertile. This is the first time we have been able to prove conclusively that male baby exposure to cigarette toxins in pregnancy and early life will damage later life fertility.

"We now know that exposure to cigarette toxins directly affects the stem cell population in the testes, causing a permanent reduction in the population of sperm produced. We also know that oxidative stress induced by these toxins causes damage to the nuclei and mitochondria (the cell's 'power' supply) of cells in the testes and this results in sperm with abnormal heads and tails, that are unable to swim properly or successfully bind and fuse with eggs.

"The findings are relevant to human health as many men, now in their 30s and 40s, were exposed to cigarette toxins in the womb when it was less well known that smoking affected babies' health.

"These men have difficulty conceiving and this is associated with production of low numbers of poor quality sperm in their semen. Unfortunately about 25 per cent of young women today continue to smoke when they are pregnant and/or breast feeding – thereby potentially damaging their sons' fertility."

Professor McLaughlin, who researches in collaboration with the Hunter Medical Research Institute's Pregnancy and Reproduction Program, said the public health message from the findings was clear.

"We would ask that smoking cessation programs continue to emphasise that women should avoid smoking in pregnancy and while breast feeding as the male germ line is very susceptible to damage during early development and the resulting sub fertility will not be apparent for several decades."

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