(ORDO NEWS) — The concentration of sperm in the semen of men has halved over the past 40 years. And this trend continues. Scientists called for urgent action to avoid further deterioration of male reproductive health.
A team of scientists from Israel, Denmark, Brazil, Spain and the United States conducted a meta-analysis that updated their previous data on the decrease in the concentration of sperm in the semen of men. It turned out that the average fell by 51.6% over 45 years.
In 2017, the same publication published the work of the same group of researchers, in which they presented the results of an analysis of all publications in English for 1981-2013 containing information on the number of sperm in men in North America, Europe, Australia and New Zealand.
The findings were disturbing. However, at that time, due to lack of data, scientists were unable to trace similar trends for the inhabitants of South and Central America, Asia and Africa.
In 2020, they decided to fill this gap and analyzed the results of several dozen more scientific papers, eventually obtaining 223 studies, providing 288 evaluations of sperm samples taken in 1973-2018 from 57,168 people from 53 countries on six continents.
Participants were divided into two groups: the first included young men who did not know if they were fertile; in the second – those who have already become fathers, and partners of pregnant women, including with the help of IVF, but regardless of the outcome of the pregnancy.
Men with confirmed infertility or low fertility (inability to conceive and/or give birth to a healthy child without medical assistance) were excluded from the sample.
According to the results of a meta-analysis, sperm concentrations decreased markedly – minus 0.87 million per milliliter annually, from 101.2 million per milliliter in 1973 to 49.0 million per milliliter in 2018.
Among men from the first group, who lived on all the studied continents, this indicator fell by 51.6% over 45 years.
Moreover, the decline was especially noticeable in the data after the beginning of the 21st century: the process accelerated twice – from 1.16% after 1972 to 2.64% after 2000 annually.
In general, the trends were similar for the total sperm count. Its sharp decline was revealed in the adjusted meta-regression model for all men – minus 2.06 million for the year.
“After stratifying by fertility group and adjusting for all covariates, including continent, there was a strong decrease in total sperm count among men who did not know their fertility level (minus 4.70), but not among fertile ones (minus 0.24).
In men from the first group, the total sperm count from 1973 to 2018 fell by 1.40% per year and by 62.3% in general, ”the researchers specified.
According to them, although both studied parameters – the total number of spermatozoa and their concentration in the semen – cannot be considered a reliable indicator of the ability to conceive a child, they are closely related. And the findings point to a serious public health problem.
“The relationship between sperm concentrations and time to conception is non-linear. Beyond the 40-50 million per milliliter threshold, higher concentrations do not necessarily mean an increased chance of conception.
On the other hand, below this threshold, the odds drop rapidly.
At the population level, the decrease in sperm concentration from 104 million to 49 million per milliliter, which we are talking about in our work, implies a significant increase in the proportion of men with a delayed conception time, ”the scientists explained.
Thus, if sperm concentrations continue to drop at the current rate, they will fall below the threshold of 40 million per milliliter in the coming decades.
Then, according to Hagai Levin of the Hebrew University of Jerusalem, the first author of the new study, the crisis could reach a tipping point and the consequences would be irreversible.
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