Evidence for decreasing quality of semen during past 50 years.
Level 3 - non-randomized controlled study
Systematic review and meta-regression of observational historical cross-sectional studies.
PubMed 1393072 · doi:10.1136/bmj.305.6854.609
What was done
The authors reviewed publications on semen quality among men without a history of infertility identified through Cumulated Index Medicus, Current List (1930–1965), and MEDLINE (1966–August 1991). Across 61 studies published between 1938 and 1991 comprising 14,947 men, linear regression weighted by sample size was performed to examine temporal changes in mean sperm density and mean seminal volume.
What was found
Mean sperm count decreased significantly from 113 x 10(6)/ml in 1940 to 66 x 10(6)/ml in 1990 (p < 0.0001). Mean seminal volume also significantly decreased from 3.40 ml to 2.75 ml (p = 0.027).
Why it matters
This landmark paper provided the first broad statistical evidence of a substantial secular decline in human sperm concentration and volume over the latter half of the 20th century.
Limits
Data were aggregated across heterogeneous historical studies spanning decades with non-standardized counting methodologies, unadjusted variations in abstinence times, and differing geographical recruitment sources. The linear model may oversimplify non-linear regional or secular variations.
Cited by
- supports The Carlsen study out of Denmark claimed that human sperm counts had declined by 50% over a 50-year period.