CNN

Over the past 50 years, human sperm count appears to have dropped by more than 50% worldwide, according to an updated review of the medical literature.

If the results are confirmed and the decline continues, this could have important implications for human reproduction. The researchers say it could also be a harbinger of declining health in men in general, since sperm quality can be an important marker of overall health.

The examand its findings, triggered a debate among male fertility experts. Some say the results are real and urgent, but others say they are unconvinced by the data because sperm counting methods have changed so much over time that it is not possible to compare the historical and modern figures.

Almost all experts agree that the matter requires further study.

“I think one of the fundamental functions of any species is reproduction. So I think if there’s a signal that reproduction is declining, I think that’s a very important finding,” said said Dr. Michael Eisenberg, a urologist at Stanford Medicine who was not involved in the review.

“There is a strong link between a man’s reproductive health and his overall health. So that could also talk about that, that maybe we’re not as healthy as we used to be,” he said.

Others say that although the review was well done, they are skeptical of its findings.

“The way semen analysis is done has changed over the decades. He got better. It’s become more standardized, but not perfectly,” said Dr. Alexander Pastuczak, surgeon and assistant professor at the University of Utah School of Medicine in Salt Lake City. He did not participate in the examination.

“Even if you were to take the same semen sample and run it and do a semen analysis in the 1960s and 70s versus today, you would get two different answers,” he said.

Pastuczak says that in more contemporary semen analysis studies, those that rely on samples analyzed by a different method, “you don’t see these patterns.” In fact, some studies in parts of northern Europe show that sperm counts are increasing over time, not decreasing, he said.

The new analysis updates a review published in 2017 and includes new data from Central and South America, Asia and Africa for the first time. It was published in the journal Human Reproduction Update.

An international team of researchers combed through nearly 3,000 studies that recorded male sperm counts and were published between 2014 and 2020, years that had not been included in their previous analysis.

The researchers excluded studies that only presented men evaluated for infertility, those that selected only men with normal sperm counts, and those in which study participants were selected based on abnormalities or genital diseases. They only included studies published in English, those with 10 or more men and those with participants whose semen had been collected in the usual way and counted using a device called a haemocytometer.

In the end, only 38 studies met their criteria. They added them to the studies included in their previous review and extracted their data, which was fed into models.

Overall, the researchers determined that sperm count fell by just over 1% per year between 1973 and 2018. The study concluded that globally, the average sperm count had fell 52% in 2018.

When the study researchers limited their analysis to certain years, they found that the decline in sperm count seemed to accelerate, from an average of 1.16% per year after 1973 to 2.64% per year. year after 2020.

“It’s really remarkable that the decline is increasing,” said study author Dr. Hagai Levine, an epidemiologist and public health researcher at the Braun School of Public Health and Community Medicine.

At the population level, the average sperm count fell from 104 million to 49 million per milliliter from 1973 to 2019. The normal sperm count is judged more than 40 million per milliliter.

The study authors say they did not have enough data from different regions to be able to say whether some countries had lower average sperm counts than others or whether sperm counts were declining faster in certain regions. . Data from 53 countries were included in the review.

The authors also did not examine what might be causing the decline. “That should be investigated,” Levine said.

In other research, Levine says, he and others have identified certain factors associated with low sperm count.

Damage to reproductive health can begin in the womb.

“We know that maternal stress, maternal smoking, and especially exposure to man-made chemicals in plastic, such as phthalates, disrupt the development of the male reproductive system,” Levine said.

Lifestyle can also play an important role. Obesity, lack of physical activity and diets high in ultra-processed foods can all be culprits, he said.

“The same factors that affect overall health are usually also harmful to sperm quality,” he said.

One expert said that ultimately trying to do this type of study runs into problems that complicate the results.

“The document is very scientifically or statistically sound and summarizes well the data available in our field. But it’s important to recognize that this data is still very limited in how it was collected and reported,” said Dr. Scott Lundy, a urologist at the Cleveland Clinic who was not involved in the research.

Sperm counting standards and methods have changed significantly over time, Lundy says, making it difficult to compare modern counts to historical data.

Yet, he said, that historical data is all that is available on the ground.

“Although this is not a cause for panic, because the counts are overall still normal, on average, there is a risk that they will become abnormal in the future, and we must recognize this and investigate further,” Lundy said.