About 41 million Americans have prediabetes—blood sugar levels that are higher than normal, but not yet at the level of type 2 diabetes . People can lower their risk for diabetes by exercising daily and losing excess weight. Drinking coffee may also diminish risk, as studies have shown that coffee drinkers are less likely to develop type 2 diabetes than non-coffee drinkers. The reason for coffee’s protective effect is unclear, but it is theorized that caffeine may play a role.

A study in the June 26, 2006 Archives of Internal Medicine examined the link between coffee intake—both decaffeinated and regular—and diabetes risk in postmenopausal women. Compared with women who drank no coffee, women who drank six or more cups of decaf coffee daily had a 33% lower risk of type 2 diabetes; those who drank six or more cups of any type of coffee each day had a 22% lower risk.

About the Study

University of Minnesota researchers tapped into the Iowa Women’s Health Study (WHS), which tracked the health status of postmenopausal women from 1986-1997. The Minnesota study focused on a subgroup of 28,812 women who did not have type 2 diabetes when the WHS began. At the outset of the study, women completed a food frequency questionnaire, on which they estimated their average yearly intake of various foods, including decaf and regular coffee. Subsequent surveys asked about changes in health status, such as being diagnosed with diabetes. After 11 years, the researchers compared coffee intake between the women who developed type 2 diabetes and those who did not.

Women who drank the most coffee, more than six cups per day of either decaf or regular, were 22% less likely to develop type 2 diabetes than coffee abstainers. To isolate the role of caffeine, researchers divided coffee drinkers by type. The decaf drinkers showed an even greater benefit—a 33% lower risk of type 2 diabetes than women who drank no coffee. Those drinking caffeinated coffee showed little benefit over abstainers. These findings were adjusted to remove the effects of known diabetes risk factors.

This study is limited by its reliance on the volunteers to accurately report coffee habits and health changes and the possibility of other confounders that the research did not take into account.

How Does This Affect You?

Should you boost your decaf coffee intake to prevent diabetes? No. This study does not prove that decaf coffee prevents type 2 diabetes; it only shows that a high coffee intake and a lower diabetes risk occurred in the same women. Because this is an observational study—researchers collected data, but did not intervene in the women’s lives—it cannot prove cause and effect. Perhaps there is another trait common to the decaf drinkers that reduced diabetes risk.

These findings do agree with previous studies, also observational, that reported a link between coffee and diabetes. However, this recent work casts doubt on caffeine’s role in risk reduction, as the greatest effect was seen among decaf drinkers. Until researchers better understand the link between coffee and diabetes, lifestyle modifications remain the cornerstone of type 2 diabetes prevention. Take the following steps to reduce your risk:

  • Engage in 30 minutes per day of moderate physical activity
  • Choose a healthy diet rich in vegetables and whole grains
  • Pay attention to portion sizes
  • If you carry excess weight, strive to lose 5-10% of body weight

Even though coffee–decaffeinated or regular–cannot be relied upon to prevent diabetes, you needn’t worry so much about having that extra cup or two.