Sperm counts may be falling around the world, study finds

A new survey of global data has found that sperm counts in men around the world are falling – not necessarily resulting in infertility. The conclusion, however, is still the subject of debate among specialists.

A systematic review, which consists of analyzing the results of previous studies, carried out by the researchers had already been published, in 2017, on concentration and total sperm count in men from North America, Europe and Oceania. In it, the decrease had already been observed.

Paula Intasqui Lopes, who did not author the article and is coordinator of the graduate program in urology at Unifesp (Federal University of São Paulo), explains that sperm concentration consists of measuring the number of millions of gametes in each ml. The total count is the multiplication of this concentration by the total ejaculate.

“A man had a concentration of 15 million spermatozoa per ml, but he ejaculated 2 ml. So, the total count is 30 million”, he exemplifies.

After the first study indicated a drop in sperm levels, the same researchers published, on the 15th, a new version of the systematic review in the journal Human Reproduction Update with information from Central and South America, Africa and Asia, in addition to the data from other regions.

The result was a compilation of 223 surveys with more than 57,000 semen samples. Among the authors of the article is Anderson Martino-Andrade, professor at the Department of Physiology at UFPR (Federal University of Paraná).

“There was already evidence [da queda na quantidade de espermatozoides]but needed confirmation through a more robust methodology”, says Martino-Andrade.

In the review, the more than 200 studies were divided into two categories: one with surveys that selected men without considering their fertility status – these were called unselected– and another with investigations with proven fertile men.

This point expresses a bottleneck in the research, says Lopes. According to her, the survey compiled data from heterogeneous studies that did not aim to observe the concentration or count of sperm.

“Several different men were put together in these so-called unselected studies,” he summarizes.

Lopes also mentions that sperm count technologies have evolved over time, and the review considered studies from 1973 to 2018. Thus, comparing research from decades ago with more recent surveys may result in a deviation in the conclusion of the review.

The points, however, are contested by Martino-Andrade. The co-author states that the review considered only studies with the same gamete counting methodology.

In addition, he argues that the group called unselected has the characteristic of more faithfully reflecting the male population because it does not have a previous parameter of participation.

Decline in sperm volume

Analyzes of more than 200 studies point to a drop of about 26 million for each ml of sperm concentration. For the measure of total sperm count, the decline was 92 million.

However, when stratifying the studies by fertility profile, it is observed that the decrease occurred mainly in studies that did not consider the fertile status of the participants. In these surveys, the decline in sperm concentration is 52 million per ml. On the other hand, in studies done only with fertile men, the drop is only 5 million.

Martino-Andrade explains that, although it is not the only factor related to fertility, the number of spermatozoa influences reproductive capacity. Therefore, in studies that include only fertile men, it is normal to expect that the average drop will be smaller compared to the sample selected without considering this criterion.

Reasons and impacts

The drop in sperm volume does not have an explanation, but Lopes says that there are associations with tumor in the testicle, problems in the production of hormones and even hypertension.

Data from the study may also contribute to another hypothesis. One estimate concluded that, among men without proven fertility, the annual rate of decline in gamete concentration from the year 2000 was 2.6%. On the other hand, considering from 1976 onwards, this rate was 1.1%.

Lopes says that, if the drop actually occurs, this metric may indicate that the change in habits in recent years causes problems in sperm formation. “Nowadays, we have a more busy, more sedentary life, with more polluted air, the level of obesity has increased a lot.”

Even so, she points out that a reduction in sperm levels does not in itself indicate infertility. She states that there are cases of men with low concentrations of gametes that are fertile, while others with high amounts present infertility.