The admonition of a group of scientists about the status of sperm produced by men in developed nations has not gone unnoticed, although it has been described by some as exaggerated.
According to a study published in the journal Human Reproduction Update of the University of Oxford in the United Kingdom, sperm quality of men in North America, Europe and Australia has been halved in the last 40 years.
Hagai Levine, a public health researcher at the Hebrew University of Jerusalem and a leading epidemiologist, said he was "very concerned" about what this could mean if this trend continues in the future.
"Eventually this could be a problem," Levine told the BBC. "It could mean the extinction of the human species."
Other scientists who were not involved in the study praised the quality of the research, but said it is still premature to come to a conclusion like that.
Decreases quality and quantity
Levine's research gathered the results of 185 studies conducted between 1973 and 2001, which analyzed semen samples of nearly 43,000 men.
This makes it one of the largest investigations done in this area.
Levine found a 52.4% decrease in sperm concentration and a decrease in sperm count of 59.3% in men from North America, Europe, Australia and New Zealand.
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The study also indicates that the rate of decline among men living in these countries is continuous and possibly even increasing.
The shortcomings of previous research
In contrast, there were no significant decreases in sperm quality in South America, Asia and Africa, but researchers report that there are far fewer studies in these continents.
Several previous studies have shown a sharp decline in sperm count in economically developed countries, but skeptics say a large portion of these studies have been flawed.
Some have investigated a relatively small number of men or have included only men attending fertility clinics, making them more likely to have poor sperm quality.
There are also concerns related to the fact that studies showing a decrease in sperm count are more likely to be published in scientific journals than those who do not.
Another difficulty is that the first methods for the sperm count could have overestimated the actual count .
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The sum of all these factors may have created the false vision of falling sperm quality.
Researchers, however, claim to have taken into account some of these deficiencies, which has lessened the skepticism of some scientists .
"I have never been particularly convinced by the number of studies published so far that show that human sperm quality has declined in the recent past," says Dr. Allan Pacey, an academic at the University of Sheffield Reproductive Medicine Unit in United Kingdom.
"The study of Dr. Levine and his colleagues, however, addresses many of the shortcomings of previous studies."
Causes of decline
Professor Pacey believes that although Levine's study reduces the chances of errors, it does not completely remove them.
For this reason, he says, their results should be treated with care .
"The debate has not yet been resolved and there is still a lot of work to be done," says Pacey.
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"However, the study does represent a step forward in the clarification of information that will ultimately allow us to define better studies to examine this issue."
There is no clear evidence to explain the apparent decrease in the amount of sperm tozoids. However, it has been associated with exposure to chemicals used in plastics and pesticides, obesity, tobacco , stress, a diet high in saturated fats and sedentary lifestyle .
Dr. Levine, author of the study, says it is urgent to find out why sperm quality is declining and find ways to change that trend.
"If we do not change the way we live and the environment and chemicals we are exposed to, I am very concerned about what will happen in the future."
well we don't have a people shortage yet lol
but at this rate we may all get an award
yes XD!