People who increased the amount of coffee they drank each day by more than one cup over a four-year period had a 11% lower risk for type 2 diabetes than those who made no changes to their coffee consumption, according to a new study led by Harvard School of Public Health (HSPH) researchers. In addition, the study found that those who decreased their coffee consumption by more than a cup per day increased their type 2 diabetes risk by 17%.

"Our findings confirm those of previous studies that showed that higher coffee consumption was associated with lower type 2 diabetes risk," said Shilpa Bhupathiraju, lead author and research fellow in the Department of Nutrition at HSPH. "Most importantly, they provide new evidence that changes in coffee consumption habit can affect type 2 diabetes risk in a relatively short period of time."

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The study appears online Thursday, April 24, 2014 in Diabetologia (the journal of the European Association for the Study of Diabetes).

The researchers analyzed data on caffeinated and decaffeinated coffee, and caffeinated tea consumption from 48,464 women in the Brigham and Women's Hospital-based Nurses' Health Study (1986-2006), 47,510 women in Nurses' Health Study II (1991-2007), and 27,759 men in the Health Professionals Follow-up Study (1986-2006). Participants' diets were evaluated every four years with a questionnaire, and those who self-reported type 2 diabetes filled out additional questionnaires. A total of 7,269 cases of type 2 diabetes were documented.

Results showed that participants who increased their coffee consumption by more than one cup per day (median change=1.69 cups/day) over a four-year period had a 11% lower risk of type 2 diabetes in the subsequent four years compared to those who made no changes in consumption. (A cup of coffee was defined as eight ounces, black, or with a small amount of milk and/or sugar.) Those who lowered their daily coffee consumption by more than one cup (median change=2 cups/day) had a 17% higher risk for diabetes. Changes in decaffeinated coffee consumption and caffeinated tea consumption were not associated with changes in risk for type 2 diabetes.

"These findings further demonstrate that, for most people, coffee may have health benefits," said Frank Hu, senior author and professor of nutrition and epidemiology at HSPH. "But coffee is only one of many factors that influence diabetes risk. More importantly, individuals should watch their weight and be physically active."