Physicians Raymond Bunge and CM Kinloch Nelson noticed something unusual happening in an Iowa clinic in the early 1970s. It was that the number of men seeking fertility treatment was increasing. To investigate whether there were changes in sperm in the general male population, the researchers examined sperm samples from 386 men who were probably of childbearing potential, i.e. men who wanted elective vasectomy. . Bunge and Nelson were shocked by the results. Compared with men in several previous studies, these men had low semen volume, high abnormal sperm count, and low sperm concentration. The researchers speculated that some environmental factor must be affecting the population as a whole.
Since Bunge and Nelson published their findings in their 1974 paper, there have been various studies comparing sperm quality between studies. Some of these papers measured sperm count, the estimated total number of sperm in a semen sample, while others measured sperm concentration, the number of sperm in a given volume of ejaculate. (For simplicity, this article will refer to both as sperm count.) Some studies have shown a decrease. Some show an increase. Others show no change at all. Complicating matters, studies show that sperm counts vary by age, frequency of ejaculation, season, geographic location, use of marijuana and alcohol, type of underwear, clinic versus home collection. It means that These counts can vary even within a single sample.
These factors make it difficult to compare sperm counts between different study populations. Thus, although some large-scale analyzes of previous research suggest that sperm counts have declined significantly worldwide since the 1970s, a few researchers believe that this finding is inconclusive. warns that it is far from
Paper published in August 2022 Nature Reviews Urology “While it is not possible to conclude from the available data that human semen quality is declining worldwide or in Western countries, trends have been observed in some specific regions.” I’m here. The idea of a global decline in sperm counts is an ‘important hypothesis, but the data are not good’ [enough] We need to be able to draw conclusions,” said Dolores Lamb, an andrology researcher at Weill Cornell University, who was not involved in the study.
Lam et al. explain that many factors can affect sperm count. First, sperm move, but not all studies fix sperm before counting. Semen is not always well-mixed and may vary within samples. “All these things add up to prove that sperm counting is a very difficult and flawed practice,” says Alan Pacey, a andrologist at the University of Sheffield in England. “And we know it clinically. That’s why it’s so hard to predict someone’s fertility from a single semen sample.”
Currently, one of the most accurate methods of assessing sperm count is using flow cytometry, an automated tool that can count and analyze each sperm individually. However, that method was not available when many older studies were conducted. Very large analyzes comparing old and new studies often exclude analyzes that use newer methods and instead require researchers to count sperm in chambers with grids, which is more common. Preference is given to simpler techniques, which are error-prone techniques.
Another problem with these large analyzes is that most of the individual studies are , they said, were not designed to determine whether sperm counts were changing in any particular population.with paper Nature Reviews Urology. A notable exception is the Danish study. The study was conducted in response to a startling analysis published in 1992 suggesting a decrease in sperm count. A Danish study collected semen samples from recruits, a relatively homogeneous demographic group, for 15 years and found no evidence of decline during that time.
In contrast, other studies point to a decrease. Epidemiologist Haggai Levin of the Hebrew University of Jerusalem and his colleagues published an analysis in 2017 evaluating more than 200 studies using counting chambers in total, with an update coming in 2022. These two papers of his found that since the 1970s, sperm concentrations have declined by about 50 percent, especially in Western countries. Levine said he did not expect small differences in aggregation methods between studies to account for the overall large declines observed on average. In other words, he believes there is enough data to show a decline that he can make it compelling.
“It’s true that when you combine data from many study cohorts, there are concerns about differences between studies,” says Lydia Minguez Alarcon, a reproductive epidemiologist at Harvard’s TH Chan School of Public Health. However, she believes that large-scale analyzes showing declines explain these differences. “The opinion of many reproductive epidemiologists is that sperm counts are declining in Western countries,” she says. For non-Western countries, she argues, data are lacking to say one way or the other. A 2022 update by Levine and colleagues suggests that sperm counts are also down in South America, Asia and Africa, but Levine notes that studies in these regions are scarce.
Other researchers acknowledge that fertility rates are declining in many countries, but question the reasons behind it. “Birth rates are declining, but I don’t know if it’s biological,” says Pacey. About 1 in 6 women experience infertility, and this can be for a variety of reasons. Pacey suspects that social and economic factors play an important role. She may be waiting longer for couples to have children and people are having sex less often. Sperm count is also an imprecise measure of fertility. Some data suggest that a higher sperm count shortens the time to conception, but it is still possible to reach conception with a low sperm count.
Some studies have noted a strong association between obesity and infertility, possibly due to its impact on semen quality. And obesity rates are increasing. Environmental endocrine disruptors such as phthalates and bisphenol A (BPA) are also thought to be associated with decreased sperm counts. Ambient temperature also affects sperm counts, and increased global temperatures could hypothetically affect fertility.
“Sperm counts are highly influenced by the environment and our lifestyles, because sperm are being manufactured all the time,” says Levine. And even if his estimates of a large global decline were off, say, “only 20 percent, 10 percent.” [or] 5% is true, but some of the causes can be irreversible, so it’s better to wait and see. “
Most people in the field agree that more research is needed on this issue. Levine and Marion Bouricoe, director of interdisciplinary research and community at the Harvard Institute for Gender Science, point out that male fertility research has long been neglected. Levine said that if systematic studies were done around the world, not only would we know if the decline was continuing or could be in the future, but the shifts were linked to obesity, alcohol consumption, and exposure to chemicals. It will also help scientists better understand whether it is caused by factors such as exposure, he said.
“It’s embarrassing that, after 30 years, we still don’t have an answer that everyone agrees on on an issue of such importance,” says Pacey.
