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Declining semen quality: can the past inform the present?
1Department of Family and Community Medicine, University of Missouri, Columbia 65212, USA. shswan@ibmonet
Summary
Historical sperm count data, despite potential variability, appears reliable for trend analysis. Studies suggest a significant decline in sperm density over time, which cannot be explained by counting methods or population factors alone.
Area of Science:
- Reproductive biology
- Environmental health
- Epidemiology
Background:
- Sperm counts have been clinically used since 1929 for infertility assessment.
- Recent studies indicate a potential decline in sperm count or density.
- A controversial 1992 analysis reported a 50% decrease in sperm density between 1938 and 1990.
Purpose of the Study:
- To critically evaluate the reliability of historical sperm count data.
- To investigate potential methodological or population-based explanations for observed declines in sperm density.
- To determine if historical sperm density data can be trusted for trend analysis.
Main Methods:
- Analysis of 61 historical studies on sperm density.
- Examination of trends in sperm counting methods and study variability.
- Statistical analysis to account for potential confounding factors like abstinence time.
Main Results:
- No significant trends in sperm counting methods or their variability were found.
- Statistical adjustments alone could not explain the observed decline in sperm density.
- Controlling for population characteristics, such as abstinence duration, amplified the estimated rate of decline.
Conclusions:
- Historical sperm density data, despite inherent random error, are surprisingly reliable for trend analysis.
- Methodological variations and population characteristics do not fully account for the observed decrease in sperm density.
- Further contemporary data are needed to understand the causes of temporal and geographic variations in sperm density.