Temporal trends in sperm count: a systematic review and meta-regression analysis.
Level 3 - non-randomized controlled study
Systematic review and meta-regression of observational studies
PubMed 28981654 · doi:10.1093/humupd/dmx022
What was done
A systematic review and meta-regression analysis of English-language studies published between 1981 and 2013 evaluating human sperm concentration (SC) and total sperm count (TSC) from semen samples collected between 1973 and 2011. Following screening of 7,518 abstracts and 2,510 full texts, 244 estimates from 185 studies comprising 42,935 men were analyzed. Temporal trends were evaluated using simple linear regression and weighted meta-regression models adjusting for age, abstinence time, collection/measurement methods, fertility group ('Unselected' vs. 'Fertile'), and geographic group ('Western' [North America, Europe, Australia, New Zealand] vs. 'Other' [South America, Asia, Africa]).
What was found
Overall SC declined significantly between 1973 and 2011 (adjusted meta-regression slope: -0.64 million/ml/year; 95% CI: -1.06 to -0.22; P = 0.003). Geographic location significantly modified the slope (P = 0.027). Among unselected Western men, SC fell by 1.4% per year (-1.38 million/ml/year; 95% CI: -2.02 to -0.74; P < 0.001), totaling a 52.4% decline over the study period. A smaller decline occurred in fertile Western men (-0.68 million/ml/year; P = 0.033), whereas no significant trends were detected in non-Western populations. Total sperm count in unselected Western men declined by 1.6% per year (-5.33 million/year; 95% CI: -7.56 to -3.11; P < 0.001), representing an overall 59.3% decline. In data restricted to post-1995 collections, steep declines persisted in unselected Western men (SC slope: -2.06 million/ml/year; TSC slope: -8.12 million/year).
Why it matters
This study provides systematic meta-analytic confirmation of a substantial 50% to 60% decline in sperm counts over nearly four decades in Western nations, signaling significant implications for male reproductive health and overall fertility.
Limits
The analysis relies on historical observational datasets with heterogeneous semen collection protocols and counting techniques across decades. Data for non-Western regions were sparse, limiting conclusions outside of North America, Europe, Australia, and New Zealand. Aggregate meta-regression cannot establish causality or identify specific environmental or lifestyle drivers.
Cited by
- supports Total motile sperm count, sperm concentration, and sperm quality in men have experienced a progressive decline since 1973.