More or Less Is RFK right about US sperm counts?
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Dec 6, 2025 Professor Allan Pacey is an expert in male fertility from the University of Manchester, while Adith Arun is a Yale researcher specializing in testosterone data. They dissect a controversial claim about declining sperm counts and testosterone levels among U.S. teenagers compared to older men. Pacey highlights the complexities in sperm quality studies, while Arun reveals how changes in testing methods have distorted testosterone trends. Both warn against misinterpretation leading to unnecessary treatments that could harm fertility.
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Historical Sperm Data Are Unreliable
- There is no direct evidence that the average US teenager now has half the sperm count of a 65-year-old man.
- Historic comparisons are flawed by differing populations, counting techniques, and changing definitions of "normal."
1992 Study Compared Apples And Oranges
- The landmark 1992 study that sparked concern compared different kinds of men across decades, biasing results.
- Earlier counts overestimated sperm due to poorer techniques, inflating apparent declines.
Meta-Analyses Give Conflicting Results
- Recent meta-analyses disagree: some report big global falls while others show no US decline.
- The 2023 global meta-analysis used heterogeneous data with the same comparability problems as earlier work.