According to a report published in The Journal of Agricultural and Food Chemistry (Dec 28 2011), a group of scientists headed up by Drs. Ling Zheng and Kun Huang believe that coffee's inhibitory effect on type 2 diabetes is due to two substances in the brew -- caffeic acid and chlorogenic acid. A bit of background:
So far the news about coffee and diabetes has come from correlating the results of a number of large-scale population-based studies. Researchers in a couple of different parts of the world have used the data collected in these studies to determine if there was a pattern between coffee consumption and later development of diabetes 2. The one most people are familiar with is based on the Nurses' Health Study, which started in 1975. Thousands of nurses have been filling out questionnaires about their daily habits, including how much coffee they drink for 35 years. Researchers found that nurses who reported drinking 4 or more cups of coffee a day had a 50% lower risk of developing type 2 diabetes, and the more coffee they reported drinking, the lower their risk of diabetes went. They also found that it didn't matter if the nurses were drinking decaf coffee.
That data was backed up by a number of other studies, including one that compared a large cohort of Finnish twins. That data was particularly interesting because it found that in twins -- genetically identical and with similar early childhood backgrounds but with different coffee-drinking habits -- those who drank more coffee (more than 7 cups a day in this study) were less likely to develop type 2 diabetes.
All of the studies concluded that coffee has a definite inhibitory effect on the development of type 2 diabetes and suggested that further research be done to determine which compounds in coffee might be responsible.
That's the starting ground for the Chinese study recently released. The researchers focused on recent research that linked human islet amyloid polypeptide (hIAPP), also called amylin, with type 2 diabetes. Amylin is secreted by the pancreas at the same time as insulin and works with insulin to help control glucose levels in the blood. It's been known for a while that pateints with type 2 diabetes show a larger concentration of amylin residues in the pancreas than those who don't have diabetes. The researchers decided to see which, if any, compounds in coffee might affect the concentration of amylin. They tested the inhibitory effects of caffeine, caffiec acid and chlorogenic acid on the aggregation of hiAPP and found that all three substances inhibit the development of toxic levels of hiAPP -- but caffeic acid and chlorogenic acid had a much greater effect than caffeine.
Those findings may also explain why some studies have found that filter coffee doesn't have quite the same effect as coffee brewed in other ways -- filter coffee typically has less acids than French press coffee or espresso. Robusta, which is often mixed into espresso blends to give them an "edge", also has a higher content of chlorogenic and caffeic acid than arabica beans.
Of course, this means that if these findings are confirmed, some big pharmaceutical company will be working on synthesizing caffeic acid and chlorogenic acid and putting them into a pill for people to take. But wouldn't it be kinda cool for your doctor to tell you "Drink 3 espressos and call me in the morning?"