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A woman drinking coffee

Coffee may reduce risk of type 2 diabetes

A new study shows reductions in the risk of type 2 diabetes, especially when the coffee is decaffeinated

By Deane Morrison

June 27, 2006

If you're regularly shelling out $3.50 a pop for a fancy 12-oz. latte, you may be getting a benefit besides the exercise of walking to the coffee shop. A new study led by Mark Pereira, associate professor in the University's School of Public Health, found that coffee drinkers had a slightly reduced risk of developing type 2 diabetes compared to those who don't drink coffee. The effect was stronger in drinkers of decaffeinated coffee. The study followed postmenopausal subjects in the Iowa Women's Health Study from 1986 to 1997. The researchers examined coffee intake and new cases of type 2 diabetes in 28,812 women who had neither type 2 diabetes nor cardiovascular disease at the outset. For those who drank no coffee, the rate was 177 new cases of type 2 diabetes among 2928 women, or 6 percent. For subjects who drank six or more cups of coffee a day, the rate was reduced to about 4.7 percent. If only decaffeinated coffee intake was considered, the rate dropped to about 4 percent.

"The risk reduction associated with coffee is independent of factors such as weight and physical activity," says Pereira.

Overall, there were 1,418 new cases of type 2 diabetes, or about 4.9 percent. The diabetes rates for coffee drinkers were adjusted to match the controls in such variables as presence or absence of hypertension, diet, physical activity, and tea consumption. Tea consumption of more than four cups a day also seemed to help reduce the risk of diabetes. "The risk reduction associated with coffee is independent of factors such as weight and physical activity," says Pereira in a news release. "There appears to be great potential for coffee to help reduce the risk of diabetes. Identifying the mechanism responsible for this should definitely be the subject of further research." Coffee, as any connoisseur knows, is a rich blend of many different compounds and flavors, of which some may well improve the metabolism of carbohydrates and therefore delay the onset of type 2 diabetes. One compound, chlorogenic acid, may reduce the absorption of the sugar glucose from the gut, among other actions. Also, coffee is loaded with antioxidants that may protect the insulin-producing beta cells in the pancreas from wear and tear or may keep other tissues from becoming resistant to insulin. When tissues become insulin-resistant, they no longer respond to the hormone by taking up glucose from the blood, and blood glucose levels tend to stay high. Insulin resistance is a hallmark of type 2 diabetes. The role of caffeine intrigued the researchers, who were unable to identify a clear risk or benefit associated with caffeine intake. "Perhaps high caffeine intake carries more detrimental effects in older adults than in middle aged adults, or perhaps the association between caffeine and diabetes in the present study was confounded by some unmeasured or poorly measured factor," the researchers write in their article. The article cites a 12-year study of Finnish coffee drinkers that showed continued strong reductions in the risk of type 2 diabetes as coffee intake increased, even to 10 cups a day. Finns drink little decaffeinated coffee, so the study was not able to draw a clear line between the effects of regular versus decaf. More than 20 milion Americans have diabetes, 6.2 million of them undiagnosed. These include both type 1 diabetes, in which the beta cells can't produce insulin, and the much more common type 2 diabetes, in which insulin is produced but to little or no avail. Besides Pereira, Emily Parker and Aaron Folsom of the School of Public Health were authors of the study. The work was supported by the National Cancer Institute.

To learn more about the University's efforts to combat diabetes, read Defeating diabetes and All our trials.