Men who smoke when they are trying for a family could raise the risk of their children suffering cancer.
Doctors last night urged would-be fathers to give up the habit in the same way as women are urged to stop smoking.
Researchers in Perth, Australia, said: ‘Women who intend to start a family are informed that smoking during pregnancy can have adverse effects on the health of the baby but the anti-smoking message is not often directed at potential fathers.
'Men should be strongly encouraged to cease smoking, particularly when planning to start a family.’
They questioned the parents of 388 children with acute lymphoblastic leukaemia, an illness of the white blood cells which is the most common childhood cancer. It affects one in 2,000 children and 15 per cent will not survive.
The scientists found that the mothers’ smoking behaviour had no impact on the risk of cancer. But sufferers whose fathers smoked at all at conception were 15 per cent more likely to develop the cancer.
Those whose fathers smoked at least 20 cigarettes per day around that same time were 44 per cent more likely to be diagnosed with the disease, the American Journal of Epidemiology reports.
Elizabeth Milne, who specialises in the causes of childhood damage at Perth’s Telethon Institute for Child Health Research, said that poisons in tobacco smoke are known to damage the DNA in sperm.
She said that this sub-quality sperm can still reach and fertilise an egg, which may lead to health problems in the resulting baby.
However, the study could not prove that the man’s smoking raised the odds of the child’s cancer.
Dr Allan Pacey, a male fertility expert from Sheffield University said: ‘There have been several studies suggesting that the risk of a child developing acute lymphoblastic leukaemia was increased if their fathers were smokers.
'This paper adds further weight to that theory and as a consequence I would agree that it is good advice for both men and women who are trying to start a family to give up smoking.
'The sperm production process takes about three months from start to finish so couples planning pregnancy should bear this in mind. Stopping smoking on Friday will not lead to an improvement in sperm DNA by Monday. But stopping smoking in December may see things get better by March.’