Drinking four cups of coffee every day can decrease a woman's risk of developing Type 2 diabetes by more than half, according to a new study.
And the researchers say they've uncovered the reason why the new findings and other research have suggested a link between java and diabetes. They found that coffee raises the amount of sex hormone-binding globulin (SHBG) in the blood, and higher levels of SHBG are known to lower the risk of developing Type 2 diabetes.
It's likely something in the coffee besides the caffeine — or something about coffee drinkers that confers these protective effects, said James D. Lane, an associate research professor at Duke University Medical Center, who was not involved with the study.
Although, "it's impressive to find these new things," Lane told MyHealthNewsDaily, more research is needed to confirm the link.
The study is published in this month's issue of the journal Diabetes.
The more you drink, the lower your diabetes risk
In the new study, researchers from the University of California, Los Angeles, compared the medical histories and coffee-drinking habits of 359 women who had diabetes with those of 359 healthy women over 10 years. They used information from the Women's Health Study, run by the National Institutes of Health.
Women who drank four cups of caffeinated coffee a day had higher levels of SHBG and were 56 percent less likely to develop Type 2 diabetes than women who don't drink coffee, the researchers found.
And the more coffee the women drank, the more their risk of developing Type 2 diabetes dropped, the study said.
Furthermore, when the researchers took into account the women's SHBG levels, they found that it was coffee's effect on SHBG levels that was making the difference in diabetes risk. SHBG regulates the levels of sex hormones in the blood.
Previous work had suggested a link between SHBG and diabetes. A 2009 study in the New England Journal of Medicine, done by one of the researchers of the new study, showed that higher levels of SHBG in the blood were associated with a lower risk of developing Type 2 diabetes.
Past evidence of protection
A causal link between SHBG, diabetes and coffee — which contains many compounds — is not clear, Lane said. For example, he pointed to a 2004 study in journal Diabetes Care, which showed that caffeine is harmful to people with Type 2 diabetes, because it hinders the breakdown of glucose.
But other past studies have shown that something in coffee seems to have a protective effect against Type 2 diabetes, he said.
A 2006 study in the journal Archives of Internal Medicine of 28,812 women found that those who drank six cups of decaffeinated coffee a day had a 22 percent lower risk of developing Type 2 diabetes than those who don't drink any coffee. Caffeinated coffee also seemed to have a protective effect, though not as strong as that of decaffeinated coffee, the researchers said.
And a 2009 study in the same journal showed that each daily cup of coffee or tea cut the risk of developing diabetes by 7 percent.