Sperm concentrations in Western men have declined by more than 50 per cent over the past 40 years, according to a major new study.

The study, led by Israeli researchers, reviewed hundreds of studies into sperm quality between 1973 and 2011.

In all, 43,000 men were studied.

“These findings strongly suggest a significant decline in male reproductive health, which has serious implications beyond fertility concerns,” the authors said.

Researchers found an increasing proportion of men had sperm counts below the threshold for infertility.

“The high proportion of men from Western countries with concentration below 40 million/ml is particularly concerning, given the evidence that sperm concentration below this threshold is associated with a decreased monthly probability of conception,” the authors said.

Lifestyle could be to blame: scientists

Professor Rob McLachlan from the Hudson Institute of Medical Research in Melbourne said it was too soon to know if the fall in sperm count would be reflected in natural conception rates.

“This latest analysis presents the challenge to identify and address potential negative impactors on male fertility such as lifestyle, obesity and comorbidities that are rising in developed countries particularly, and generally the role of environmental toxicants for which there is certainly evidence in more select populations,” he said.

Professor McLachlan, who was not involved in the study, said the men who were tested included those with no concerns about their fertility and those who have had children.

He said a decline in sperm concentration was found in both groups.

Reproductive toxicologist Dr Shaun Roman from the University of Newcastle said the role of diet and environment would need to be vigorously investigated.

“However, it should be noted that it only takes one sperm to fertilise an egg and, on average, western men are still producing 50 million per ejaculate,” he said.

“We are not in crisis yet.”

They suggested future research should focus on identifying lifestyle factors behind falling sperm count.

“Research on causes and implications of this decline is urgently needed,” the authors said.

There was no reduction in sperm decline in men in South America, Asia and Africa, but the researchers said limited studies from those countries could be to blame.

The research was published in the Human Reproduction Update Journal.

− ABC