Does caffeine lower testosterone levels in men? Original paper

Caffeine is the most commonly used psychoactive drug in the world and may provide many health benefits.^[1] However, caffeine has also been implicated in a number of adverse health outcomes.^[2] For instance, caffeine has been linked to impaired reproductive function and low testosterone in male rats.^[3] Yet, as more evidence is mounting, the results of these studies have become increasingly conflicting and inconclusive. Also, it’s unclear how different caffeine metabolites — the most abundant ones being theophylline, paraxanthine, and theobromine — influence the association between caffeine and testosterone.

This cross-sectional study of 372 U.S. adult men (average age of 47) examined the association between serum testosterone levels and urinary levels of caffeine as well as 14 caffeine metabolites.

Higher caffeine levels were linked to lower testosterone levels in men. Also, most of the caffeine metabolites (10 of 14) were also linked to lower testosterone levels. Only 3 of the 14 caffeine metabolites were linked to higher testosterone levels, while one metabolite showed no significant association.

Of the three most common caffeine metabolites, theophylline showed the greatest association with low testosterone levels (approximately three times greater than caffeine itself). Theobromine also showed a small association with low testosterone levels. In contrast, paraxanthine was associated with higher testosterone levels.

Due to the cross-sectional nature, this study cannot draw any true cause-and-effect conclusions between caffeine, its major metabolites, and testosterone levels. Also, the researchers were unable to determine the caffeine source (e.g., tea, coffee, or soda), which could influence its effect on testosterone levels and reproductive health.