Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries.
Level 3 - non-randomized controlled study
Systematic review and meta-regression of observational and cross-sectional studies.
PubMed 36377604 · doi:10.1093/humupd/dmac035
What was done
Authors searched PubMed/MEDLINE and EMBASE for studies on human sperm concentration (SC) and total sperm count (TSC) published between 2014 and 2019. Combining newly identified studies (38 studies, 44 estimates) with an earlier meta-analysis, the final dataset comprised 223 studies and 288 estimates from semen samples collected between 1973 and 2018. Simple linear regressions and weighted meta-regressions were adjusted for predetermined covariates, fertility status (unselected vs. fertile), and geographic region (North America-Europe-Australia [NEA] vs. South/Central America-Asia-Africa [SAA]), with subset analyses for samples collected post-2000.
What was found
Across all studies, simple linear modeling showed SC declined by -0.87 million/ml/year (95% CI: -0.89 to -0.86; P < 0.001). In adjusted meta-regression, SC declined among unselected men in NEA (-1.27 million/ml/year; 95% CI: -1.78 to -0.77; P < 0.001), unselected men in SAA (-0.65; -1.29 to -0.01; P = 0.045), and fertile men in NEA (-0.50; -1.00 to -0.01; P = 0.046). Overall, unselected men experienced a 51.6% drop in mean SC between 1973 and 2018 (-1.17 million/ml/year; -1.66 to -0.68; P < 0.001), with a steeper decline in samples collected post-2000 (-1.73 million/ml/year; -3.23 to -0.24; P = 0.024; rate increasing from 1.16%/year post-1972 to 2.64%/year post-2000). Total sperm count among unselected men declined by 62.3% over the study period (-4.70 million/year; -6.56 to -2.83; P < 0.001).
Why it matters
This study extends previous findings of declining sperm counts beyond Western nations to South/Central America, Asia, and Africa, indicating a worldwide trend that appears to be accelerating in the 21st century.
Limits
The total number of individual participants is not reported in the abstract. As a meta-regression of historical observational datasets, results are susceptible to variations in laboratory protocols, participant selection criteria, and unmeasured environmental or lifestyle confounders over a 45-year span. Potential causal drivers of the decline were not evaluated.
Cited by
- supports Total motile sperm count, sperm concentration, and sperm quality in men have experienced a progressive decline since 1973.