Whenever people discuss sports supplements, and the topic of irrefutable performance enhancers is raised, caffeine always makes it onto the list of everyone’s favorite. Although prevailing wisdom is that people consume an overabundance of caffeine in their daily lives, usually it’s the opposite when we talk about athletes consuming enough to get a true ergogenic effect – I’ve found that people get caffeine-a-phobic when I tell them to take 400+ milligrams prior to training.
But what effect does taking a huge dose of caffeine prior to training, on top of your regular caffeine intake, have over the long term? We can point to numerous studies that show a health benefit from coffee drinking, many of which are not found with the consumption of the decaffeinated species, but what about the inevitable day when drinking one (or two or three) cups of coffee stops giving you the same effects? Receptor downregulation is a fact of life and is to be expected with nearly every chemical we consume.
While we know about the various neurotransmitters and adenosine receptors that are effected by caffeine, we know little about caffeine’s effects on sex hormones, namely testosterone, estrogen, and sex hormone binding globulin (SHBG). What, if any, effect does our daily cup of java have on these hormones?
After eight weeks, very little, it turns out. But at four weeks, during what may still be rightly termed the adaptation phase, there are some striking differences between groups of caffeinated versus noncaffeinated coffee drinkers. For the male group, drinking caffeinated coffee increased (!) total testosterone and decreased total and free estradiol. Is there some kind of anti-estrogenic/aromatase inhibitive effect going on here? It certainly seems so, right? However, for women, caffeinated coffee only increased total testosterone, while decaffeinated coffee decreased both total and free testosterone, with no effects on estrogen reported.
Here’s the study:
Nutr J. 2012 Oct 19;11(1):86. [Epub ahead of print]
The effects of caffeinated and decaffeinated coffee on sex hormone-binding globulin and endogenous sex hormone levels: a randomized controlled trial.
Wedick NM, Mantzoros CS, Ding EL, Brennan AM, Rosner B, Rimm EB, Hu FB, van Dam RM.
BACKGROUND: Findings from observational studies suggest that sex hormone-binding globulin (SHBG) and endogenous sex hormones may be mediators of the putative relation between coffee consumption and lower risk of type 2 diabetes. The objective of this study was to evaluate the effects of caffeinated and decaffeinated coffee on SHBG and sex hormone levels.
FINDINGS: After a two-week run-in phase with caffeine abstention, we conducted an 8-week parallel-arm randomized controlled trial. Healthy adults (n = 42) were recruited from the Boston community who were regular coffee consumers, nonsmokers, and overweight. Participants were randomized to five 6-ounce cups of caffeinated or decaffeinated instant coffee or water (control group) per day consumed with each meal, mid-morning, and mid-afternoon. The main outcome measures were SHBG and sex hormones [i.e., testosterone, estradiol, dehydroepiandrosterone sulfate].No significant differences were found between treatment groups for any of the studied outcomes at week 8. At 4 weeks, decaffeinated coffee was associated with a borderline significant increase in SHBG in women, but not in men. At week 4, we also observed several differences in hormone concentrations between the treatment groups. Among men, consumption of caffeinated coffee increased total testosterone and decreased total and free estradiol. Among women, decaffeinated coffee decreased total and free testosterone and caffeinated coffee decreased total testosterone.
Our data do not indicate a consistent effect of caffeinated coffee consumption on SHBG in men or women, however results should be interpreted with caution given the small sample size. This is the first randomized trial investigating the effects of caffeinated and decaffeinated coffee on SHBG and sex hormones and our findings necessitate further examination in a larger intervention trial.