This episode of More or Less examines a specific statistical claim made by US Health Secretary Robert F. Kennedy, Jr. regarding sperm counts and testosterone levels. Host Lizzie McNeil is joined by Professor Alan Pacey, an andrology expert from the University of Manchester, and later references research by medical graduate Adif Arun.
Kennedy claimed the average US teenager has only 50% of the sperm count and testosterone of a 65-year-old man. Professor Pacey explains that sperm production quantity generally remains stable with age, though quality can deteriorate. The discussion centers on studies about declining sperm counts, starting with a heavily criticized landmark 1992 study that compared different populations over decades. Methodological issues, like varying definitions of "normal" sperm count and outdated counting techniques that overestimated concentrations, plague historical comparisons. Kennedy likely referenced a 2023 meta-analysis reporting a 50% global decline, but this data faces similar comparability challenges. Factors like required abstinence periods before testing cause sperm counts to fluctuate even in the same individual. A 2025 meta-analysis found no discernible decrease in sperm counts among US men across generations. Professor Pacey notes that of various studies, 21 show no decline, eight show a decline, and six have ambiguous results. He concludes that even if a decline exists, it represents a change from one normal range to another, unlikely to impact fertility for most men.
The analysis finds no evidence supporting Kennedy's claim about teenage sperm counts being half those of older men. On testosterone, the show explains levels naturally decline about 1% per year after age 30. Prescriptions for testosterone replacement therapy (TRT) in the US grew from 7.3 million to 11 million between 2019 and 2024, with use rising among younger men. Adif Arun investigated data suggesting a spike in low testosterone cases but discovered a critical change in testing methodology from immunoassays to mass spectrometry. The diagnostic threshold for "low" testosterone was historically 300 ng/dL based on older immunoassay results. Modern mass spectrometry is more accurate, leading the Endocrine Society to recommend a new threshold of 264 ng/dL. When Arun adjusted the data to account for this methodological shift, the apparent dramatic decline in testosterone levels disappeared. A concerning irony is that unnecessary TRT use is a proven cause of infertility and lowered sperm count.
The tone is educational and investigative, systematically deconstructing a public claim by examining scientific literature and data methodology. The style is conversational but precise, featuring expert interviews to clarify complex topics.
Listeners interested in data literacy, public health statistics, and the science behind sensational headlines would appreciate this episode. Those seeking a definitive, simple answer on demographic health trends without a nuanced look at research challenges might find it less engaging.
