With a seemingly constant barrage of stories about “too
much of a good thing” being bad for us (see: junk food, time
spent on the Internet, etc), it’s nice to get some news that
something many of us love (and some would admit we’re
addicted to) is actually healthier for us in larger doses.
Coffee has shown it may be protective against type 2 diabetes in
numerous studies, yet no one has really understood why -- until
now.
Researchers at UCLA have discovered a possible molecular mechanism
behind coffee's protective effect.
A protein called sex hormone-binding globulin (SHBG) regulates the
biological activity of the body's sex hormones -- testosterone and
estrogen -- which have long been thought to play a role in the
development of type 2 diabetes. The less SHBG one has in their
body, the more susceptible they are to developing the
disease.
And coffee consumption, as it turns out, increases blood levels of
SHBG.
Reporting with colleagues in the current edition of the journal Diabetes, the study’s first author Atsushi Goto, a UCLA doctoral student in epidemiology, and Dr. Simin Liu, a professor of epidemiology and medicine with joint appointments at the UCLA School of Public Health and the David Geffen School of Medicine at UCLA, show that women who drink at least four cups of coffee a day are less than half as likely to develop diabetes as non-coffee drinkers.
For the study, the researchers identified 359 new diabetes cases matched by age and race with 359 apparently healthy controls.
The participants were selected from among nearly 40,000 women enrolled in the Women's Health Study, a large-scale cardiovascular trial originally designed to evaluate the benefits and risks of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer.
The researchers found the women who drank four cups of caffeinated coffee each day had significantly higher levels of SHBG than did non-drinkers and were 56 percent less likely to develop diabetes than the non-drinkers.
And those who also carried the protective copy of the SHBG gene appeared to benefit the most from coffee consumption.
When the investigators controlled for blood SHBG levels, the decrease in risk associated with coffee consumption was not significant. Liu said this suggests it is SHBG that mediates the decrease in risk of developing type 2 diabetes.
The American Diabetes Association estimates that nearly 24 million children and adults in the U.S. -- nearly 8 percent of the population -- have diabetes.
Type 2 diabetes is the most common form of the disease and accounts for about 90 to 95 percent of these cases.
According to Liu, early studies have consistently shown an "inverse association" exists between coffee consumption and risk for type 2 diabetes. That is, the greater the consumption of coffee, the lesser the risk of diabetes.
It was thought that coffee may improve the body's tolerance to glucose by increasing metabolism or improving its tolerance to insulin.
"But exactly how is elusive," said Liu, "although we now know that this protein, SHBG, is critical as an early target for assessing the risk and prevention of the onset of diabetes."
Earlier work by Liu and his colleagues published in the New England Journal of Medicine had identified two mutations in the gene coding for SHBG and their effect on the risk of developing type 2 diabetes; one increases risk while the other decreases it, depending on the levels of SHBG in the blood.
A large body of clinical studies has implicated the important role of sex hormones in the development of type 2 diabetes, and it's known that SHBG not only regulates the sex hormones that are biologically active but may also bind to receptors in a variety of cells, directly mediating the signaling of sex hormones.
"That genetic evidence significantly advanced the field," said Goto, "because it indicated that SHBG may indeed play a causal role in affecting risk for type 2 diabetes."
"It seems that SHBG in the blood does reflect a genetic susceptibility to developing type 2 diabetes," Liu said. "But we now further show that this protein can be influenced by dietary factors such as coffee intake in affecting diabetes risk -- the lower the levels of SHBG, the greater the risk beyond any known diabetes risk factors."
While this is great news for java fanatics, those who choose to go decaffeinated shouldn’t get too excited over these findings.
"Consumption of decaffeinated coffee was not significantly associated with SHBG levels, nor diabetes risk," Goto said. "So you probably have to go for the octane!"
Other authors of the study included Brian Chen of UCLA and Julie Buring, JoAnn Manson and Yiqing Song of Brigham and Women's Hospital and Harvard Medical School. Funding was provided by the National Institutes of Health.
