Muscle-building steroids make men infertile

Men taking steroids and anti-baldness medications to appear more attractive may be inadvertently reducing their fertility, warn two scientists.

This evolutionary paradox, dubbed the Mossman-Pacey paradox, was described in a letter published in the Journal of Internal Medicine.

Dr James Mossman at Brown University in Providence, Rhode Island and Professor Allan Pacey at the University of Sheffield said that men who are attempting to look more attractive by taking anabolic steroids are in fact damaging their fertility, and have a 90 percent chance of becoming sterile.

Anabolic steroids can increase muscle mass as they mimic the function of testosterone, however this can trick the pituitary gland into thinking the testes are overactive. In order to compensate, the pituitary then reduces the production of the FSH and LH hormones - which are also vital for the production of sperm. 

The authors also note that there is a similar outcome in men attempting to limit hair loss by taking a medication called finasteride which also changes the way testosterone is metabolised. 

Dr Mossman told the BBC that while such vanity-based medications may make you more attractive, they could turn you into an 'evolutionary dud'. 

He first noticed the connection between steroid abuse and low fertility when studying for his doctorate at Sheffield.

'I noticed some men coming in to have their fertility tested and these guys were huge. They are trying to look really big, to look like the pinnacles of evolution,' he said. 'But they are making themselves very unfit in an evolutionary sense, because without exception they had no sperm in their ejaculation at all.'

Although the link between steroids and low fertility has been known for some time, Dr Mossman and Professor Pacey believe that there needs to be more education about the side-effects of steroid use among young men.

Also speaking to the BBC, Professor Pacey said: 'The irony is one thing, but I think the key message is for fertility patients.

'It keeps cropping up in clinics and the message is not getting out to young men that it's a problem and a bit of info could save them a lot of heartache.'