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. Overall, SC declined appreciably between 1973 and 2018. In an adjusted meta-regression model, which included two interaction terms declines were seen among unselected men from NEA. Among unselected men from all continents, the mean SC declined by 51.6% between 1973 and 2018. The slope for SC among unselected men was steeper in a model restricted to post-2000 data 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 in the adjusted meta-regression model. All results changed only minimally in multiple sensitivity analyses.
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.