More than 125,000 study participants who were free of diabetes, cancer, and cardiovascular disease at the start of a study were selected from the on-going Health Professionals Follow-up Study and the Brigham and Women's Hospital-based Nurses Health Study. Some 41,934 men were tracked from 1986 to 1998 and 84,276 women from1980 to 1998 via food frequency questionnaires every two to four years to assess their intake of both regular and decaffeinated coffee.

During the span of the study, 1,333 new cases of type 2 diabetes were diagnosed in men and 4,085 among the women participants. The researchers also found that for men, those who drank more than six cups of caffeinated coffee per day reduced their risk for type 2 diabetes by more than 50 percent compared to men in the study who didn't drink coffee. Among the women, those who drank six or more cups per day reduced the risk of type 2 diabetes by nearly 30 percent. Decaffeinated coffee was also beneficial, but its effects were weaker than regular coffee.

The research was supported by a grant from the National Institutes of Health. The findings appeared in the Jan. 6, 2004 issue of the Annals of Internal Medicine.