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Hagai Levine, Niels Jørgensen, Anderson Joel Martino‐Andrade | Human Reproduction Update | (2022)
Key Takeaways
Plain English Takeaway
Men around the world are making less sperm than they used to, and this drop is happening faster now than before.
Study Aim
The study set out to find out if sperm counts (the number of sperm in semen) have changed over time for men from all continents. The researchers wanted to update their earlier work, which only had enough data from North America, Europe, and Australia. They also aimed to see if the decline in sperm counts is happening worldwide and if it is speeding up in recent years.
Simply put: The study wanted to see if men everywhere are making less sperm now than in the past.
Study Design
The researchers performed a systematic review and meta-regression analysis (a way to combine and analyze results from many studies over time). They searched for studies published between 2014 and 2019 that reported sperm concentration and total sperm count. They included 44 new estimates from 38 studies and combined these with data from their previous review, totaling 223 studies and 288 estimates from 1973 to 2018. They used statistical models to look for trends over time and checked if results were different by continent or fertility status. They also ran sensitivity analyses to test the strength of their findings.
Simply put: The study combined results from hundreds of studies about sperm counts from 1973 to 2018 to see how things have changed.
Findings
The research demonstrates that sperm concentration and total sperm count have dropped sharply worldwide from 1973 to 2018. Among men not selected for fertility problems, sperm concentration fell by 51.6% and total sperm count by 62.3%. The decline was seen in men from North America, Europe, Australia, South/Central America, Asia, and Africa. The rate of decline has doubled since 2000, meaning sperm counts are dropping faster now. The authors argue that this is the first analysis to show a decline in sperm counts among men from South/Central America, Asia, and Africa. They recommend urgent research into the causes and prevention of this trend to protect male reproductive health.
Simply put: Sperm counts are falling everywhere, and the drop is speeding up, so scientists need to find out why and how to stop it.
Abstract
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. OBJECTIVE AND RATIONALE: 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. SEARCH METHODS: We searched PubMed/MEDLINE and EMBASE to identify studies of human SC and TSC published during 2014-2019. After review of 2936 abstracts and 868 full articles, 44 estimates of SC and TSC from 38 studies met the protocol criteria. Data were extracted on semen parameters (SC, TSC, semen volume), collection year and covariates. Combining these new data with data from our previous meta-analysis, the current meta-analysis includes results from 223 studies, yielding 288 estimates based on semen samples collected 1973-2018. Slopes of SC and TSC were estimated as functions of sample collection year using simple linear regression as well as weighted meta-regression. The latter models were adjusted for predetermined covariates and examined for modification by fertility status (unselected by fertility versus fertile), and by two groups of continents: NEA and SAA. These analyses were repeated for data collected post-2000. Multiple sensitivity analyses were conducted to examine assumptions, including linearity. 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. WIDER 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.
Referenced In
Created: May 19, 2026