Summary Background Numerous studies have reported decreases in semen quality and other markers of male reproductive health. A recent meta-analysis reported a significant decrease in sperm concentration (SC) and total sperm count (TSC) among North American-Europe-Australian (NEA) men based on studies published during 1981-2013. At the time, there were too few studies using data from South America/Central-Asia-Africa (SAA) to reliably estimate trends among men on these continents. Objectives and rationale The goal of this study was to examine trends in sperm count among men across continents . The broader implications of a global decline in sperm count, the knowledge gaps left unfilled by our previous analysis, and the controversies surrounding this issue warranted an updated meta-analysis. Methods PubMed/MEDLINE and EMBASE were searched to identify human SC and TSC studies published during 2014–2019. After review of 2936 abstracts and 868 full articles, 44 SC and TSC estimates from 38 studies met the protocol criteria. Data on semen parameters (SC, TSC, semen volume), year of collection, and covariates were extracted. 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 between 1973 and 2018. The slopes of SC and TSC were estimated as functions of collection year of the sample 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. These analyzes were repeated for the data collection chosen after 2000. Multiple sensitivity analyzes were performed to examine assumptions, including linearity. Results Overall, SC decreased significantly between 1973 and 2018 (slope in 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 [fertility time group (P ¼ 0.012) and time continents (P ¼ 0.058)], decreases were observed among unselected NEA men (-1.27 ; -1.78 to -0.77; P < 0.001) and unselected men from SAA (–0.65; –1.29 to –0.01; P ¼ 0.045) and fertile men from NEA (–0. 50; –1.00 to –0.01; P ¼ 0.046). Among unselected men from all continents, mean SC decreased by 51.6% between 1973 and 2018 (–1.17: –1.66 to –0.68; P < 0.001). The SC slope 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 percentage annual decline of the cent doubled , increasing from 1.16% after 1972 to 2.64% after 2000. Results were similar for TSC, with an overall 62.3% decrease among unselected men (–4.70 million/year; –6.56 to –2.83; P < 0.001) in the adjusted meta-regression model . All results changed minimally in multiple sensitivity analyses. Implications This analysis is the first to report a decrease 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 suggests that this global decline continues into the 21st century at an accelerated pace . Research into the causes of this continued decline and actions to prevent further disruption of male reproductive health are urgently needed . |
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An international team led by Professor Hagai Levine of the Hadassah Braun School of Public Health at the Hebrew University of Jerusalem, with Professor Shanna Swan of the Icahn School of Medicine, Mount Sinai, New York, along with researchers from Denmark, Brazil, Spain, Israel and the USA, published the first meta-analysis to demonstrate the decrease in sperm count among men in South and Central America, Asia and Africa.
Alarmingly, this study also shows that the decline in sperm counts in North America, Europe and Australia, reported by this team in 2017, has continued and even accelerated in the 21st century. Sperm count is not only an indicator of human fertility; It is also an indicator of men’s health , as low levels are associated with a higher risk of chronic diseases, testicular cancer, and shorter life expectancy.
The authors say the decline reflects a global crisis related to our modern environment and lifestyle, with broad implications for the survival of the human species.
This latest analysis, with data from 53 countries , was published in the journal Human Reproduction Update . It includes seven additional years of data collection (2011-2018) and focuses on sperm count trends among men in regions not previously reviewed, specifically South America, Asia, and Africa.
The data show, for the first time, that men in those regions share the significant decline in total sperm count (TSC) and sperm concentration (SC) previously observed in North America, Europe and Australia. Furthermore, this study shows an accelerated decline after 2000 in TSC and SC globally. As Levine summarized these results, "Overall, we are seeing a significant global decline in sperm count of more than 50% over the past 46 years, a decline that has accelerated in recent years."
While the current study did not examine the causes of decreased sperm count, Levine pointed to recent research indicating that alterations in reproductive tract development during fetal life are linked to impaired fertility throughout life. and other markers of reproductive dysfunction. Additionally, Levine explained that "lifestyle choices and chemicals in the environment are negatively affecting this fetal development . "
Time is running out, Levine warned. “Our findings serve as a canary in a coal mine. We have a serious problem on our hands that, if not mitigated, could threaten the survival of humanity. "We urgently call for global action to promote healthier environments for all species and reduce exposures and behaviors that threaten our reproductive health."
Swan emphasized that low sperm counts not only affect men’s fertility, but have serious ramifications for men’s health in general, and are linked to other adverse trends, collectively called testicular dysgenesis syndrome.
“The concerning declines in men’s sperm concentration and total sperm count by more than 1% each year, as reported in our article, are consistent with adverse trends in health outcomes for other men, such as testicular cancer, hormonal disruption and congenital genital defects, as well as deterioration in female reproductive health. "This clearly cannot continue unchecked."
Conclusion and broader implications Our new data and analyzes confirm our previous findings of a measurable decline in sperm count between 1973 and 2018 among men in North America, Europe, and Australia and support a decline among unselected men in South/Central America, Africa, and Asia. . This decline has continued, as our previous analysis predicted, and has become more pronounced since 2000. This substantial and persistent decline is now recognized as a major public health problem. In 2018, a group of leading doctors and scientists called on governments to recognize declining male fertility as a major public health issue and to recognize the importance of male reproductive health to the survival of the human (and other) species. . Research is needed into the causes of this continued decline and an immediate focused response is needed to prevent further disruption of male reproductive health. We hope that the new evidence provided here will receive the attention not only of doctors and scientists, but also of decision makers and the general public. |
