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According to a new analysis conducted in Israel and the United States, men have fewer and fewer sperms confirming a phenomenon that had already been detected in a large and controversial study published in 2017. Between 1973 and 2018, on average, the amount of sperms in human sperm it more than halved, declining by about 1 percent each year until 2000, when an even steeper annual decline began to be recorded, by more than 2.6 percent.
The new analysis, published this week in the scientific journal Human Reproduction Update, is based on data from 53 countries in South America, Asia and Africa, geographic areas for which there was not much data for the previous study published in 2017. According to the research team, the reduction of sperm in those parts of the world is comparable to what was found in Europe, Australia and North America. The study does not examine the causes of this reduction, but brings important new data to give a dimension to the phenomenon, which has been explored for over 50 years.
The seminal fluid, or semen, is made up of various substances which favor the maintenance and movement of the spermatozoa, the male gametic cells which have the task of reaching the egg (female gamete) and fertilising it, triggering the process which leads to pregnancy.
With each ejaculation, an adult man produces between 1.5 and 5 milliliters of sperm with a concentration of sperm per milliliter which varies greatly, depending on the conditions of each subject: the World Health Organization indicates values higher than 15 million sperm per milliliter. A reduced quantity of sperm can affect the ability to fertilize, although other factors must not be excluded, such as the ability of individual sperm to move, and to do so with sufficient speed to reach the egg.
The first studies reporting a reduction in sperm were published between the 1970s and 1980s, but at the time the extent of the phenomenon was not yet very clear. In the scientific community there was much discussion about the results of those researches, also because other studies had not found particular declines or a general reduction in the quality of the sperm. Furthermore, there were no shared standards for assessing the extent of the problem, and for this very reason the World Health Organization launched some initiatives, in order to find common references for studies on male infertility.
Thanks to greater coordination between researchers and some important advances in analysis systems, more in-depth and reliable research was published starting in the 1990s, indicating a reduction in sperm concentration. One of the most important works was published in Denmark in 1992 and compared the main studies on the subject produced up to then, concluding that in the previous 50 years there had been a significant reduction in sperm and the quantity of sperm produced. The analysis led to a wealth of new research, not only on the functioning of the male reproductive system, but also on the psychological and social implications of declining fertility.
In 2017 a meta-analysis, i.e. an analysis of numerous studies on the subject published over the years conducted at the Hebrew University of Jerusalem, found a 52.4 percent reduction in sperm concentration and a 59.3 percent reduction in sperm count between 1973 and 2011. Analyzes published later by other research centers would have led to similar data, in some cases with lower percentages, confirming the phenomenon. The recently published study of countries in South America, Asia and Africa also confirmed the reduction in sperm counts.
(Hagai Levine et al., Human Reproduction Update)
In recent times other studies have been dedicated to the analysis of sperm motility, which as we have seen is another important factor for fertility. A study published in 2019 found that the number of men with normal sperm motility had dropped by 10 percent from 16 years earlier. Overall, the majority of studies therefore indicate that men today produce fewer sperm cells than they used to, and that they are overall less healthy.
The subject is periodically taken up by newspapers and television, often with alarmist headlines, although to date neither the causes nor the implications of this so-called “male infertility crisis” are clear. A lot of research has been published over the years to explore possible causes, some focusing on health risk factors such as obesity and diabetes, others on lifestyles and exposure to particular substances.
It has long been known that some of these can cause hormonal imbalances, which then have consequences for fertility. Their effects have been found in the laboratory on animals, while it is more difficult to evaluate them on humans since they cannot conduct experiments in which they are exposed to those substances. However, research groups can find some clues by analyzing the substances present in the environments in which people who are then subjected to tests for fertility live. It is not an exact science, but it allows us to gather important elements.
Analyzes often focus on “endocrine disruptors”, molecules that can have effects similar to hormones that regulate various functions of our body, including those related to reproduction. There are many of them in objects and sometimes in food with which we are in contact every day, for this reason their use is regulated and is kept under control to limit the risks. Not being able to estimate the effects with certainty, health authorities and governments often adopt precautionary principles, limiting the quantities of substances considered to be at risk within certain thresholds. Even air pollution, mainly due to human activities, can have consequences on our body and on fertility.
Excessive alcohol consumption, smoking, lack of physical activity and unhealthy lifestyles in general can affect sperm count reduction. Obesity is an often overlooked risk factor, despite the fact that in more developed societies it is a condition that affects significant portions of the population.
Studies on male fertility problems are still highly debated, above all because at the moment no important effects on the birth rate attributable to this problem have been found. Despite the significant decline found in the more extensive analyses, in absolute terms the concentration of spermatozoa still remains higher than the 15 million per milliliter indicated by the WHO, which however previously indicated the threshold at 20 million.