In your column on Smoking & Fertility, you wrote that smoking can damage DNA in men's sperm. You also say that for women, "the effects of smoking would be nil if you stop smoking three months before conception." What about for men? How long should I give up smoking before impregnating my wife? Richard

Research has shown that men who smoke cigarettes may have higher levels of abnormal-appearing sperm as well as evidence of DNA (chromosome) damage. Since sperm production takes roughly 90 days, the effect of smoking on sperm DNA should be minimal by three months after you quit.