The study is not the first to document this association. However, in previous studies it was unclear if the relationship was true among people of different ages and body weights and if the caffeine component was the ingredient primarily responsible for the anti-diabetes effect.

Dr. Mark A. Pereira, from the University of Minnesota in Minneapolis, and colleagues addressed these uncertainties by analyzing data from 28,812 women enrolled in the Iowa Women's Health Study, which ran from 1986 to 1997. All of the women were free from diabetes and heart disease when the study began.

The subjects were divided into groups based on the amount of coffee they drank: none, less than 1 cup, 1 to 3 cups, 4 to 5 cups, or 6 or more cups per day. During follow-up, 1,418 of the women were diagnosed with diabetes.

Women who drank the most coffee were 22 percent less likely to develop diabetes than the group that drank no coffee, the report indicates. Further analysis showed that this association, which remained relatively stable by age and body weight groups, was largely accounted for by intake of decaffeinated coffee rather than regular coffee.

The coffee ingredients responsible for the possible protective effect remain unclear. Two coffee components, magnesium and phytate, did not account for the association seen. Caffeine intake from all sources, including soft drinks, also had no bearing on diabetes risk.

Although the first line of prevention for diabetes is exercise and diet, in light of the popularity of coffee consumption and high rates of...diabetes in older adults, these findings may carry high public health significance."

SOURCE: Archives of Internal Medicine, June 26, 2006.