Only one in seven West Australian men involved in a new study met fertility benchmarks set by the World Health Organisation, researchers have said.

More than 400 WA men aged between 20 and 22 had testicular ultrasounds and sperm samples examined by researchers from the University of Western Australia and Perth's King Edward Memorial Hospital.

They found 85 per cent of the men failed to reach the World Health Organisation's criterion for fertility, which measures semen quality and sperm count.

The study, which has been published in the international journal Human Reproduction, found being overweight has a significant impact on a man's semen volume and sperm output.

Smoking, drinking and taking drugs were not associated with any significant semen variables.

"This is quite a shocking result from what we're led to believe is a normal population," said Michael Gannon, the president of the Australian Medical Association's WA branch.

"There's no question that in morbidly obese men you get a reduction in testosterone levels in the bloodstream and testosterone, being a key male hormone, is crucial in sperm production.

"It just adds to the whole range of risks associated with morbid obesity."

Mr Gannon said the unusual findings suggested international benchmarks may need to be reconsidered.

"I think when you start to say 85 per cent of men are abnormal, that's when you need to check your normal guidelines and this is where we need international comparisons and research," he said.

"But there's no doubt this is of concern and it shines a light on a problem we're aware of."

The men involved are all participants in the long-term Raine study, which started more than two decades ago and has tracked their development since they were babies.

Men encouraged to be more aware of their fertility

Mr Gannon said while being overweight or obese was a serious health issue, having a low sperm count should not be cause for panic.

"Thousands of us walking around today were sired by men with bad sperm counts and at the end of the day you only need one to get through," he said.

"We often only know that men have low sperm counts when their partner also has problems leading to conceiving, but this is yet another sign that there's a gradual increase in the morbidity of being overweight and obese."

Mr Gannon said the study highlighted the need to make men more aware of their fertility at a younger age.

"I think quite correctly we're talking more about the risks of delaying a family for women, but the truth is men need to be a part of that decision because it's not just the woman's responsibility," he said.

"There's no perfect time to have children, but there's no question that if people choose to delay having a family for whatever reason there might be consequences for that.

"It's always been thought that men just continue to make sperm well beyond women's menopause and of course we know men can sire children well into their 60s and 70s, but we're concerned there might be more subtle problems like an increase in autism.

"This is another area for ongoing research."