"First, a few facts to counter the horror stories: there is no conclusive proof on declining sperm counts; numbers of sperm have little bearing on fertility (it's the quality that counts); and sperm production and virility are unrelated. You can help your sperms' ability to bring about conception by keeping your weight down, decreasing sugar content, keeping your alcohol intake to a moderate amount, quitting smoking, and keeping your scrotum relatively cool. A minimum intake of zinc, selenium, and various vitamins, especially vitamin E, could be important. Infections, particularly if sexually transmitted (chlamydia, gonorrhoea), non-specific urethritis, prostatitis and mumps in adult life can all have a damaging effect on sperm production. Pesticides in contaminated food, pollution, PCBs (polychlorinated biphenyls) and oestrogen-like compounds, can all affect sperm function. Substances found in products such as cling-film and plastic cartons can leach into our food stuffs. So try not to use them in contact with food substances, particularly at increased temperatures (such as microwave cooking).

Finally, it is a simple matter to freeze sperm and preserve it for future use. So men having a vasectomy, vasectomy reversal, or undergoing cancer treatment, for example, should think about this as a form of insurance." Fiona McClymont

Dr Simon Fishel is Director of CARE (Centre for Assisted Reproduction) at the Park Hospital, Nottingham.