There has been a 60% decline in sperm count since the 1970s, the first global meta-analysis of trends in male fertility has found. Men may face a fertility crisis in the coming decades, scientists warn.

Falling sperm counts have been suspected for decades – but many of the studies that found such trends have been hampered by methodological difficulties. Many were small, inconclusive or have focused on men known to have fertility problems.

The first global study to look at both fertile and infertile men has found that sperm counts are indeed falling. It focuses on 'unselected' men – those who have no particular known medical problems related to fertility.

In addition to sperm count, the analysis of 185 studies between 1973 and 2011 found that sperm concentrations in semen have fallen by 50% in the last 50 years.

The trend was most pronounced in the US, Europe, Australia and New Zealand. Data from Asia, South America and Africa were less conclusive but also suggested a decline in sperm count.

What is causing it?

Although the latest study did not look at the causes behind the trend, it noted that factors such as exposure to chemicals in the womb or to pesticides as an adult have been linked to lowered sperm counts.

Father and baby
Scientists are calling for more research on the underlying causes of the falling sperm count. Jon DeJong

"The male reproductive system developing in utero is very sensitive to chemicals throughout endocrine system, such as maternal smoking," study author Hagai Levine of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine told IBTimes UK.

What's classed as a 'low' sperm count?

The so-called sperm count threshold for 'subfertility' in men is 40 million sperm per ml of semen. For men with this sperm count or below, it may take around 7 months to conceive.

Men with a sperm count below 15 million per ml semen are considered 'infertile'. But, confusingly, this doesn't mean that they are completely unable to have a child. It may take them and their partners more than a year to conceive, but it is still possible to do so.

The sperm count is a spectrum rather than something that can be clearly divided into categories of fertility. Even men with high sperm counts may be infertile for other reasons.

Source: Hagai Levine

"But also in adult life, we know that pesticide exposure is clearly harmful to male reproduction and the sperm count – as are lifestyle choices like smoking, stress, obesity and not getting enough physical activity. The usual suspects."

Having systematic evidence that there is a decline is a first step towards tackling its causes. For men who are already mature and thinking about having a child, the factors that may have reduced their sperm count are likely to have had an impact on them many years ago.

"What is likely to have happened is that they were affected when they were in utero. What they need to do is maximise their fertility as much as they can – not smoking, don't drink too much," said Christopher Barratt, head of reproductive medicine at the University of Dundee who was not involved in the research. However, men still can boost their chances by making lifestyle changes.

A clear picture at last

As the most conclusive piece of research on sperm count to date, the study puts to rest many of the questions that have arisen about the trend in recent decades.

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"It's the first time we've heard the message that clearly for a very long time. The message itself is very, very bad news," said Barratt.

The fact that the drop in sperm count has been continuing at a steady rate for 50 years is particularly worrying, he said.

"At this rate, men are going to be extinct in the next generation, from a sperm point of view. But thankfully biology doesn't really work that way – it's not going to continue at exactly that rate I would imagine, but it is a very disturbing trend."