With commentary by Efi Koloverou, MMedSci, a clinical dietitian and doctorl degree candidate at Harokopio University in Athens

Coffee drinkers are at lower risk of developing type 2 diabetes, finds a study involving nearly 1,500 men and women. Over a 10-year period, the researchers found, people who drank about a cup and a half of Greek-style coffee every day were 54% less likely to be diagnosed with the disease than non-drinkers.

While past research has linked coffee to reduced type 2 diabetes risk, the new study is among the first to analyze whether markers of oxidative stress and inflammation may play a role in the relationship. The researchers found that people's levels of serum amyloid A (SAA)—an inflammation-promoting protein made mostly in the liver that's been tied to increased diabetes risk—mediated the coffee-diabetes link.

In the new study, published online July 1 in the European Journal of Clinical Nutrition, Efi Koloverou, MMedSci, a clinical dietitian and doctoral degree candidate at Harokopio University in Athens, and her colleagues looked at 1,485 men and women aged 18 to 89 who were free of diabetes when they enrolled in the study, in 2001 and 2002. They divided the group into coffee abstainers, casual drinkers (meaning they had less than 250 ml of coffee daily), and habitual drinkers, who downed at least 250 ml daily.

During 10 years of follow-up, 191 study participants were diagnosed with type 2 diabetes.

Nearly 10% of the abstainers developed type 2 diabetes during the study, versus 7% of casual coffee drinkers and just over 5% of the habitual coffee drinkers. And the more coffee a person drank, the lower their diabetes risk.

Just 47 people in the study reported drinking decaffeinated coffee, so it's not possible to say whether decaf would have the same beneficial effects, Koloverou told EndocrineWeb via E-mail. “I believe though that the beneficial effect of coffee cannot be contributed to caffeine alone, for two reasons,” she said. “First, caffeinated drink consumption (that is, tea, cola) was taken into account and did not alter the protective association of coffee drinking on diabetes outcome. Secondly, the benefit was found to be mediated by SAA, an inflammatory marker. Thus, coffee may affect pro-inflammatory cellular signaling pathways.”

According to Koloverou, circulating levels of SAA may affect glucose homeostasis. "Postchallenge hyperglycemia might be an intermediate variable linking SAA to the development of type 2 diabetes,” she explains.

The researchers defined a cup of coffee as 150 ml. This equals about 2.5 to 3 cups of brewed coffee, according to Koloverou, or about three cups of instant coffee. “So we may hypothesize, that apparently healthy individuals with no history of cardiovascular disease, may benefit from daily consumption of this amount of coffee,” she said.

While Koloverou and her colleagues found no difference in the effects of different types of coffee on diabetes risk, she explained that the number of people involved in the study was too small to figure out if different types of coffee had different effects on diabetes risk.

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