ABSTRACT

Background:
Caffeine is one of the most commonly used psychoactive drugs in the world, and provides many health benefits including alertness, improved memory, and reducing inflammation. Despite these benefits, caffeine has been implicated in a number of adverse health outcomes possibly due to effects within the endocrine system, effects that may contribute to impaired reproductive function and low testosterone in men. Previous studies have investigated associations between caffeine consumption and testosterone levels in men, although the quantity and generalizability of these studies is lacking, and the results between studies are conflicting and inconclusive.

Methods:
Using data from a cross-sectional study of 372 adult men in the 2013-2014 NHANES survey cycle, the researchers set out to characterize the association between serum testosterone levels, caffeine, and 14 caffeine metabolites.

Results:
Multivariable, weighted linear regression revealed a significant inverse association between caffeine and testosterone. Multivariable, linear regression revealed significant, inverse associations between 6 xanthine metabolic products of caffeine and testosterone. Inverse associations were observed between 5-methyluric acid products and testosterone, as well as between 5-acetlyamino-6-amino-3-methyluracil and testosterone. A significant, positive association was observed for 7-methyl xanthine, 3,7-dimethyluric acid, and 7-methyluric acid. Logistic regression models to characterize the association between 2 biologically active metabolites of caffeine (theobromine and theophylline) and odds of low testosterone (< 300 ng/dL) were non-significant.

Conclusions:
These findings suggest a potential role for caffeine's contribution to the etiology of low testosterone and biochemical androgen deficiency. Future studies are warranted to corroborate these findings and elucidate biological mechanisms underlying this association.

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