I love when scientific research fails to confirm the working hypothesis but still produces a result that is significant in some way not originally intended. In this case, researchers were looking for a link between caffeinated or decaffeinated coffee consumption and any changes in sex hormone levels, specifically sex hormone-binding globulin (SHBG), in an attempt to understand how coffee consumption can reduce the occurrence of and severity of type II diabetes.
Study participants were regular coffee drinkers, nonsmokers, and overweight. Those is the coffee groups drank five 6-ounce cups a day with meals (either caffeinated or decaffeinated), while controls drank water.
After 8 weeks, they found that SHBG is unaffected by coffee intake, with or without caffeine. Interestingly, at the 4 week point, in men who consumed caffeinated coffee, there was a statistically significant increase in total testosterone and decrease in free and total estradiol. By the eighth week, however, there seemed to be no difference between the various treatment groups.
So, first of all, the subjects were overweight, which means they had high estrogen levels to begin with most likely. So if there is some polyphenol in coffee that helps the body clear estradiol and estrogen, then testosterone levels will automatically increase. But apparently this is true after four weeks but not eight.
Secondly, eight weeks is pretty short study to examine the effects of any substance on metabolism and hormones.
Finally, it appears the caffeine is the active ingredient. BUT, caffeine anhydrous (No Doze or Vivarin) is not the same as the complex caffeine in coffee or tea. I'd bet that a study pitting an equal amount of caffeine intake versus coffee would show that only the coffee is beneficial in this way.
Most likely, the results here point to only one mechanism of how coffee impacts diabetes anyway. I would still recommend coffee to my clients who can tolerate the caffeine.
The effects of caffeinated and decaffeinated coffee on sex hormone-binding globulin and endogenous sex hormone levels: a randomized controlled trial
Nicole M Wedick, Christos S Mantzoros, Eric L Ding, Aoife M Brennan, Bernard Rosner, Eric B Rimm, Frank B Hu andRob M van Dam
Nutrition Journal 2012, 11:86 doi:10.1186/1475-2891-11-86
Published: 19 October 2012
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.
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.
The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.