High levels of testosterone decrease sperm count and impair the immune system.
"So high levels of testosterone actually decrease our sperm count and they are bad for our immune system." (said at 0:12:12)
The claim is broadly accurate but benefits from physiological context. First, high circulating or exogenous testosterone suppresses sperm production through negative feedback on the hypothalamic-pituitary-gonadal (HPG) axis, inhibiting LH and FSH release and dramatically reducing intratesticular testosterone, which is required for spermatogenesis (a mechanism leveraged in male hormonal contraceptive research). Second, androgens like testosterone exert immunosuppressive and anti-inflammatory effects (e.g., dampening antibody responses to vaccines like influenza), which can reduce immunocompetence against certain pathogens, though this property also provides protection against some autoimmune disorders.
- supports: Systems analysis of sex differences reveals an immunosuppressive role for testosterone in … (Proceedings of the National Academy of Sciences of the United States of America 2014)
"Moreover, men with elevated serum testosterone levels and associated gene signatures exhibited the lowest antibody responses to TIV. These results demonstrate a strong association between androgens and genes involved in lipid metabolism, suggesting that these could be important drivers of the differences in immune responses between males and females." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Suppression of Spermatogenesis by Exogenous Testosterone. (Current pharmaceutical design 2021)
"Exogenous administration of androgens influences the hypothalamic- pituitary-gonadal axis with negative feedback that may lead to a partial or complete cessation of spermatogenesis by decreasing FSH and LH." (abstract, background, passage verified)
pubmedfull study (doi) - supports: Testosterone and male contraception. (Current opinion in endocrinology, diabetes, and obesity 2024)
"By suppressing release of gonadotropins, these agents markedly decrease endogenous testosterone production, lower intratesticular testosterone and suppress spermatogenesis." (abstract, results, passage verified)
pubmedfull study (doi)