Steroids and exercise supplements bought over the Internet are damaging men's sperm.
A leading Irish fertility doctor says young couples are struggling to conceive as a result.
Professor Mary Wingfield says men are coming to her clinic with virtually no sperm because of supplements and protein powders bought online.
She says marathon runners and others who take part in endurance sports also risk having a low sperm count.
Approximately one in six Irish couples reported difficulty in getting pregnant and Professor Wingfield says the problems are generally connected to lifestyle, nutrition and stress rather than genetic or biological issues.
