Humans could face reproductive crisis as sperm count declines, study finds

Humans could face a reproductive crisis if action is not taken to tackle a drop in sperm count, researchers have warned after finding the rate of decline is accelerating.

Research by the same team, reported in 2017, found that sperm concentration had more than halved in the last 40 years. However, at the time a lack of data for other parts of the world meant the findings were focused on a region encompassing Europe, North America and Australia. The latest study includes more recent data from 53 countries.

Declines in sperm concentration were seen not only in the region previously studied, but in Central and South America, Africa and Asia.

Moreover, the rate of decline appears to be increasing: looking at data collected in all continents since 1972, the researchers found sperm concentrations declined by 1.16% per year. However, when they looked only at data collected since the year 2000, the decline was 2.64% per year.

Previous studies have suggested that fertility is compromised if sperm concentration falls below about 40m per ml. While the latest estimate is above this threshold, Levine noted that this is a mean figure, suggesting the percentage of men below this threshold will have have increased.

While the study accounted for factors including age and how long men had gone without ejaculation, and excluded men known to suffer from infertility, it has limitations, including that it did not look at other markers of sperm quality.

Allan Pacey, professor of andrology at the University of Sheffield, who was not involved in the work, praised the analysis, but said he remained on the fence over whether there is a decline.

However, Levine dismissed such concerns, adding that, in any case, the decline has been more pronounced in more recent years.

While it is unclear what might be behind the apparent trend, one hypothesis is that endocrine-disrupting chemicals or other environmental factors may play a role, acting on the foetus in the womb. Experts say factors such as smoking, drinking, obesity and poor diet might also play a role, and that a healthy lifestyle may help to boost sperm counts.

Prof Richard Sharpe, an expert in male reproductive health at the University of Edinburgh, said the new data showed that the trend appeared to be a worldwide phenomenon.

Sharpe said the decline could mean it takes longer for couples to conceive and, for many, time is not on their side as they are delaying trying to conceive until the woman is in her 30s or 40s, when her fertility is already reduced.