The quality of human sperm has dropped by half in the last 50 years

If the problem continues at its current pace, in less than a decade men will have trouble being fertile

Calidad del esperma

Sperm count has been decreasing for almost a century; at this rate, men will have trouble being fertile in less than a decade. Sperm concentration has also dropped to less than half, close to the threshold of infertility. In addition, the pace of the decline has doubled so far this century. These are the alarming facts revealed by the analysis of studies from 53 countries. The authors of the review did not delve into the causes, but they do refer to certain lifestyle habits and to the exposure to chemical pollutants from the fetal stage.

In 2017, EL PAÍS published an article titled “The quality of sperm in Westerners has decreased by half in 40 years.” That earlier study focused on North Americans, Australians and Europeans, as the researchers did not have enough data from other regions to determine the fertility of men in the entire world. Now, the authors of that work have published a new study with records from countries on five continents. The new research, which includes data from Latin America, Africa and Asia, shows that the decline in sperm is global.

Hagai Levine, a professor at the Hebrew University of Jerusalem and main author of the study, said in an email (regarding the headline of the 2017 article): “Now we can say, according to the data currently available: The sperm count has dropped by half in the last 50 years, globally, not just for Westerners.” The research he leads, published in the Human Reproduction Update journal, shows that sperm concentration has gone from 101 to 49 million per milliliter since 1973 (the date of the first available data). The total sperm count also shows a marked decrease, going from 335.7 to 126.6 million per ejaculate in 2018, the last year available.

The study reveals another fact that is as disturbing as it is intriguing: the pace of the decline is accelerating. While since 1973, the sperm concentration has dropped at an annual rate of 1.16%, since 2000, it has dropped at a rate of 2.64%. The acceleration is confirmed by looking at other years of the period: since 1985, the rate was 1.31% and in 1995 it rose to 1.90% per year. If this trend continues, in just five years the sperm count could drop below a threshold after which it becomes harder to have children. “Men can be considered subfertile with sperm concentrations below 40 million per milliliter, and infertile below 15 million per milliliter,” explained Dr. Levine in the 2017 article.

To Jaime Mendiola, co-author of the study and professor of preventive medicine and public health at the University of Murcia in Spain, this acceleration is the most alarming fact. “We don’t know if it will go further,” he warns. As for the causes of the global decline in sperm, everything is hypotheses. Mendiola says that exposure to chemicals and environmental pollutants could be causing a hormonal disruption of the hypothalamic-pituitary-gonadal axis that could interfere with sperm production. However, the researcher says that in addition to the current poor lifestyle habits and determining factors, prenatal exposure must be taken into account, as “the fetal stage is critical for testicular development.” So, the crisis had been brewing for decades.

Professor Shanna Swan, from the Icahn School of Medicine at Mount Sinai, in New York, points out that low sperm counts not only affect male fertility, but also have important consequences for male health in general and are related to other adverse tendencies, generically known as testicular dysgenesis syndrome. “The troubling declines in men’s sperm concentration and total sperm counts at over 1% each year as reported in our paper are consistent with adverse trends in other men’s health outcomes,” she said. “These include testicular cancer, hormonal disruption and genital birth defects.” Mendiola adds that connections have been established between poor sperm quality and “an increase in mortality and morbidity, as well as a decrease in life expectancy.”

Nicolás Garrido, director of innovation at the IVI Foundation, one of the largest assisted reproduction groups, highlights the relevance of the study: “World-class experts did it and published it in a leading journal.” IVI Group has first-hand information on this topic; in 2019, they published a study with data on the semen quality of almost 120,000 men. “We deal with infertility problems. So we asked ourselves: are men becoming more and more infertile? With 20 years of data from our clinics in the United States and Spain, we saw that the percentage of men with no sperm has been increasing.” Then they posed another question: does this have clinical relevance? “There are different treatments, depending on the severity of the problem, and we have seen that assisted reproductive treatments are increasingly complex due to the lower quality of the sperm.”

Regarding the causes, Garrido admits that singling out a guilty party or parties is not an easy task. “We know that it has to do with our lifestyle and our exposure to pollutants, but we are not rats that can be isolated in a laboratory to find out the role that each factor plays, and we are exposed to many environmental factors.” He even mentions the possible, and paradoxical, role of fertility clinics. “We have been helping couples have children for 40 years, but in the case of genetic problems, it is likely that by doing so we are passing the problem to the next generation,” he reflects. Regardless, genetic infertility only accounts for a small fraction of the problem.

Nicolás Olea, a professor at the University of Granada who has done extensive research on sperm quality in Spain, agrees with the authors of the study and with Garrido on the difficulty of determining the exact causes of the problem. Still, he mentions some possible culprits: “We suspect that the early exposure of the embryo/fetus and the child to pollutants with hormonal activity, endocrine disruptors, has a lot to do with it.” In fact, his group has published several papers on the presence of endocrine disruptors in breast milk in Spain.

The downside of all this is that, as Olea, Garrido, Levine or Mendiola say, the double exposure to pollutants – both in the womb and in adulthood – is a complex and, now confirmed, global problem. The upside is that the same humans that created the problem can fix it. That is why Levine urgently calls “for global action to promote healthier environments for all species and reduce exposures and behaviors that threaten our reproductive health.”

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