Originally published, April 2011.
Type 2 diabetes stems from the body's inability to properly use or ultimately make enough insulin, the hormone that helps regulate sugar, starches and other foods the body uses for energy. It's the most common form of diabetes and is nearing epidemic proportions in the United States, owing mostly to the increasing prevalence of obesity and consumption of processed foods with high glycemic loads.
A number of studies have linked coffee consumption to lower rates of type 2 diabetes. The latest one, from the University of California, Los Angeles, sheds new light on why coffee may be protective. The investigators focused on a protein called sex hormone-binding globulin (SHBG), which regulates the activity of testosterone and estrogen, hormones that are both believed to play a role in the development of the disease. The research team determined that coffee boosts blood levels of SHBG and found that women who drank at least four cups daily had less than half the risk of developing type 2 diabetes as those who didn't drink any coffee.
Earlier, this same research team identified two mutations in the gene that codes for SHBG. One mutation increases the risk of type 2 diabetes while the other protects against it. Research has also suggested that blood levels of SHBG can be influenced by dietary factors, including coffee consumption. Women who carry the diabetes-protective version of the SHGB gene get the most benefit from drinking coffee. Decaffeinated coffee has no effect on SHBG or the risk of diabetes.
The study was conducted among participants in the Women's Health Study, a large cardiovascular trial including nearly 40,000 women. The investigators focused on 359 postmenopausal women newly diagnosed with diabetes who were matched by age and race with another 359 healthy women from the trial. They noted that because this study focused on postmenopausal women, the results may not apply to premenopausal women or to men.
If you're a postmenopausal woman, drinking coffee might help lower your risk of type 2 diabetes. But keep in mind that lifestyle is a big influence on the well-known risk factors for this disease: being overweight and sedentary and having metabolic syndrome and insulin resistance. If you have these risk factors, don't rely on coffee alone to protect you.
In addition, consider how coffee affects the rest of your body. It can cause anxiety, insomnia, tremor, irregular heartbeat, digestive complaints, urinary tract irritation, and, for men, prostate problems. And it can be addictive.
Andrew Weil, M.D.