The number of sperm may be decreasing worldwide, says study

Over the past 50 years, sperm counts appear to have dropped by more than 50% worldwide, according to an updated medical study.

If these findings are confirmed and the decline continues, it could have important implications for human reproduction. The researchers say this would also be a harbinger of declining health for men in general, as semen quality can be an important marker of the body’s health.

O study and his conclusions sparked a debate among male fertility experts. Some say the findings are real and urgent, but others say they aren’t convinced by the data because sperm counting methods have changed so much over time that ancient and modern numbers cannot be compared.

Almost all experts agree that the subject needs further study.

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

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

Others say that while the study was well done, they are skeptical about the conclusions.

“The way semen analysis is done has changed over the decades. Improved. It has become more standardized, but not perfect,” said Dr. Alexander Pastuczak, a surgeon and assistant professor of medicine at the University of Utah in Salt Lake City. He did not participate in the study.

“Even if you took the same semen sample for analysis in the 1960s and 1970s, compared to today, you would get two different results,” he said.

Pastuczak says that in more current semen analysis studies, which rely on samples analyzed by a different method, “you don’t see these trends.” Indeed, some studies in northern European regions show that sperm counts increase over time, not decrease, he said.

Updated study adds data from more countries

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

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

The researchers excluded studies of only men who were being evaluated for infertility, studies that selected only men with normal sperm counts, and studies whose study participants were selected on the basis of genital abnormalities or disease. They only included studies published in English, with 10 or more men and those with participants whose sperm was collected in the typical way and counted using a device called a hemocytometer.

In the end, only 38 studies met these criteria. They were added to the studies included in the previous analysis and their data were extracted to feed the models.

Overall, the researchers determined that sperm counts dropped by just over 1% per year between 1973 and 2018. The study found that globally, average sperm counts dropped by 52% through 2018.

When the study researchers restricted their analysis to certain years, they found that the decline in sperm counts appeared to be accelerating, from an average of 1.16% per year after 1973 to 2.64% per 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 a population level, the average sperm count has dropped from 104 million to 49 million per milliliter from 1973 to 2019. The normal sperm count is considered to be greater than 40 million per milliliter.

Causes of decline are unknown

The study authors say they didn’t 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 areas. Data from 53 countries were included in the analysis.

The authors also did not analyze what might be causing the decline. “It should be studied,” Levine said.

In other research, says Levine, he and others have identified some factors associated with lower sperm counts.

Damage to reproductive health can start in the womb.

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

Lifestyle can also play a role. Obesity, lack of physical activity and diets high in ultra-processed foods could be to blame, he said.

“The same factors that harm health in general also tend to harm semen quality,” he said.

One expert said that ultimately trying to do this kind of study is fraught with problems that complicate findings.

“The paper is very scientifically or statistically robust and does a good job of summarizing 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 how it was reported,” said Dr. Scott Lundy, a urologist at the Cleveland Clinic who was not involved in the research.

Sperm count standards and methods have changed a lot over time, says Lundy, making it difficult to compare modern counts with historical data.

Still, he said, historical data is all that’s available to the field.

“While it’s not a cause for panic because the counts in general are still normal on average, there is a risk that they will become abnormal in the future, and we have to recognize that and study it further,” Lundy said.