Sperm concentration has declined 51 percent in the last 46 years, finds global study
A major analysis carried out by researchers in Israel, Demark, Spain, Brazil, and the U.S. has found that sperm counts are on the decline in the human population, and sperm concentrations have nearly halved in the past 46 years, a press release said.
The research team involved in this project had previously reported this trend in North America, Europe, and Australia in 2017. They have now included data from other parts of the world and found that a similar phenomenon seems to be occurring in Africa, Central and South America, and Asia as well.
What did the study find?
The study, a meta-analysis of data collected from 223 studies conducted on semen samples collected between the years 1973 and 2018, found that, on average, sperm concentration fell from an estimated 101.2 million per ml in 1973 to 49 million per ml in 2018. This is a drop of 51.6 percent in 46 years. Total sperm count during the same period fell by a whopping 62.3 percent.
Previous studies have shown that fertility rates drop when the sperm concentration falls below 40 million per ml. While the average human male may not have yet reached this mark, researchers are of the view that the number of males who have now fallen below this threshold has likely increased.
Looking at the available data, researchers were able to quantify the rate of drop in sperm concentrations and found it to be 1.16 percent. Interestingly, analysis of the data since the year 2000 showed that the rate of decline has accelerated to 2.64 percent per year since.
What are its implications for humanity?
The study conducted only looked at the trends in sperm count and concentrations and not the reasons behind their decline. Experts suggest that a mix of environmental factors and lifestyle choices might be the reason behind such drastic reductions.
Endocrine-disrupting chemicals can affect a fetus while it is still in the womb, while habits like smoking, drinking, and a poor diet throughout our lifetimes could also be causative agents for the condition.
This is likely affecting couples who are trying to conceive and may already be past their prime when it comes to fertility. Working adults often postpone having children well until they are into their late 30s or even 40s, sometimes even encouraged by workplaces.
A drop in fertility of a population as a whole might be worrisome if not handled on time. In the next four-five decades, the number of youth might reduce considerably, making it difficult to support a large number of elderly folk and sustain economies, The Guardian reported.
Even if the current sperm counts may not be alarming right away, they also have implications for male health, and they are linked to adverse events such as testicular cancer, hormonal disruption, and genital birth defects, the press release added.
The research findings were published in the journal Human Reproduction Update.
Background: Numerous studies have reported declines in semen quality and other markers of male reproductive health. Our previous meta-analysis reported a significant decrease in sperm concentration (SC) and total sperm count (TSC) among men from North America–Europe–Australia (NEA) based on studies published during 1981–2013. At that time, there were too few studies with data from South/Central America–Asia–Africa (SAA) to reliably estimate trends among men from these continents.
Aim: The aim of this study was to examine trends in sperm count among men from all continents. The broader implications of a global decline in sperm count, the knowledge gaps left unfilled by our prior analysis and the controversies surrounding this issue warranted an up-to-date meta-analysis.
Outcomes: Overall, SC declined appreciably between 1973 and 2018 (slope in the simple linear model: –0.87 million/ml/year, 95% CI: –0.89 to –0.86; P < 0.001). In an adjusted meta-regression model, which included two interaction terms [time × fertility group (P = 0.012) and time × continents (P = 0.058)], declines were seen among unselected men from NEA (–1.27; –1.78 to –0.77; P < 0.001) and unselected men from SAA (–0.65; –1.29 to –0.01; P = 0.045) and fertile men from NEA (–0.50; –1.00 to –0.01; P = 0.046). Among unselected men from all continents, the mean SC declined by 51.6% between 1973 and 2018 (–1.17: –1.66 to –0.68; P < 0.001). The slope for SC among unselected men was steeper in a model restricted to post-2000 data (–1.73: –3.23 to –0.24; P = 0.024) and the percent decline per year doubled, increasing from 1.16% post-1972 to 2.64% post-2000. Results were similar for TSC, with a 62.3% overall decline among unselected men (–4.70 million/year; –6.56 to –2.83; P < 0.001) in the adjusted meta-regression model. All results changed only minimally in multiple sensitivity analyses.
Implications: This analysis is the first to report a decline in sperm count among unselected men from South/Central America–Asia–Africa, in contrast to our previous meta-analysis that was underpowered to examine those continents. Furthermore, data suggest that this world-wide decline is continuing in the 21st century at an accelerated pace. Research on the causes of this continuing decline and actions to prevent further disruption of male reproductive health are urgently needed.