Smoking while pregnant weakens sons' fertility, mouse study suggests

Mothers who
smoke while pregnant or breastfeeding may reduce their sons' future fertility, according to research.

In the study,
male offspring of mice exposed to the equivalent of a packet of cigarettes a
day had reduced sperm counts and abnormalities in sperm shape and mobility.
Their sperm were also less able to fertilise an egg.

Lead author Professor
Eileen McLaughlin from the University of Newcastle in Australia, said: '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'.

The
researchers say their findings may explain an observed (although contested)
rise in subfertility in men now in their thirties and forties who were exposed to
cigarette toxins in the womb at a time when the damaging effects of smoking
were less well-known.

Previous studies
have shown that smoking puts the developing fetus at higher risk for a range of
complications, including growth restriction and birth defects, but the effects
on male fertility were not as well established.

Professor McLaughlin
said: '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
or tails, that are unable to swim properly or successfully bind and fuse with
eggs'.

In the
experiment researchers placed 27 female mice into a machine designed to mimic
the effects of smoking. This worked by drawing smoke into a nose-piece; the
mice had their noses introduced into the nose-piece so that they inhaled smoke
into their lungs. Twenty-seven control mice breathed normal air. After six weeks all mice were placed with
males to produce litters. Smoke exposure continued throughout pregnancy and
lactation until weaning.

Researchers
examined the 108 offspring regularly until adulthood, measuring DNA damage in
the cells that produce sperm as well as sperm count, shape and swimming
ability.

Professor
Sheena Lewis, Professor of Reproductive Medicine at Queen's University, Belfast,
who was not involved in the study, praised it as 'well-designed and
carefully executed' and explained that 'such mechanistic experiments
are impossible and unethical in humans'.

In the UK it is estimated that 25
percent of women continue to smoke while pregnant or breastfeeding.

Dr
Allan Pacey, chair of the British Fertility Society, who was not involved in
the study, said that the research 'should send an important signal to couples
about the dangers that smoking during pregnancy has on the future reproductive
health of their infant'.

He praised the
study, which is published in Human Reproduction, as 'very welcome' and
'elegantly designed'.