Passive smoking damaged the DNA of mouse sperm

Passive smoking may harm the DNA in sperm, a new study in mice has suggested. If the findings are replicated in humans, genetic defects linked to passive smoking could be passed on to children, the researchers suggest.

'Recently, the International Agency for Research on Cancer concluded that there is enough evidence to link paternal smoking in humans with increased risk of childhood cancer, suggesting that tobacco smoking causes heritable germ cell mutation in humans', explained Francesco Marchetti, of the Lawrence Berkeley National Laboratory in California, USA who was involved in the study.

Thirty-two mice were exposed to differing quantities of smoke to model the effects of low and high doses in direct and passive smoking. The frequency of genetic mutations observed in the sperm of control mice, which were not exposed to smoke, was between 1.3 - 1.5 percent. This increased to four percent for low doses and 4.7 percent for high doses in mice exposed to mainstream smoke (simulating direct smoking).

In mice administered with side-stream tobacco smoke (simulating second-hand smoke), the rates were 4.6 percent for low doses and 2.6 percent for high doses. The researchers described the results as providing 'compelling evidence in support of the argument that passive smoking should be regarded as a germ cell mutagen in humans'.

'Our data suggests that paternal exposure to second-hand smoke may have reproductive consequences that go beyond the passive smoker', conclude the researchers, led by Professor Carole Yauk of Health Canada in Ottawa.

Dr Allan Pacey, fertility expert from the University of Sheffield, said: 'What we don't know, and what we overlook, is the influence of passive smoking. I guess it's no surprise that passive smoking causes the same kind of damage, because you're just inhaling the same stuff, albeit at different levels'.

He also added that the degree of 'passive smoking' the mice were exposed to was greater than typical human levels.

Advice for fathers-to-be is clear, outlines Dr Pacey: 'If you're trying to conceive, stopping smoking is good advice and removing yourself from the influences of passive smoking. The advice to any man who wants to be a father is to stop smoking at least three months before he tries'.

The findings were reported in Proceedings of the National Academy of Sciences.