PHILADELPHIA — Drinking more coffee may reduce the risk of developing the most common form of diabetes, a study found.

Compared to non-coffee drinkers, men who drank more than six eight-ounce cups of caffeinated coffee per day lowered their risk of type 2 diabetes by about half, and women reduced their risk by nearly 30 per cent, according to the study in Tuesday's issue of Annals of Internal Medicine.

Nevertheless, experts said more research is needed to establish whether it really is the coffee or something else about coffee drinkers that protects them.

"The evidence is quite strong that regular coffee is protective against diabetes," said one of the researchers, Dr. Frank Hu of the Harvard School of Public Health. "The question is whether we should recommend coffee consumption as a strategy. I don't think we're there yet."

Type 2 diabetes, formerly called adult-onset diabetes, typically shows up in middle-aged people. The disease is on the rise and is striking more and more young people as Americans become fatter and less active.

People with type 2 diabetes either do not make enough insulin or their bodies don't use it properly. It leads to higher blood sugar levels, which over time can cause blindness, heart disease, kidney failure and nerve damage and can lead to amputations.

Caffeine has previously been found to reduce insulin sensitivity and raise blood sugar: both bad news for the body. But the researchers note that coffee, whether it is regular or decaffeinated, also contains potassium, magnesium and antioxidants that might counteract those negative effects and improve the body's response to insulin.

In the latest study, every two to four years over a period of 12 to 18 years, more than 126,000 people filled out questionnaires reporting, among other things, their intake of coffee and tea. Researchers adjusted the data for risk factors such as smoking, exercise and obesity.

There was a more modest effect among decaf drinkers: a 25 per cent risk reduction for men and 15 per cent for women. There was no statistically significant link between diabetes and tea.

The results are in agreement with those from a 2000 study of 17,000 Dutch adults, which concluded that people who drank at least seven cups of coffee a day were half as likely to develop type 2 diabetes than people who drank two cups or less.

Dr. Nathaniel Clark of the American Diabetes Association expressed concerns that such reports divert public attention toward illusory quick-fixes and away from proven diabetes-stoppers, such as diet, weight loss and exercise.

"While we're always happy when there's research looking at what people can do to reduce their risk," he said, "I'm often frustrated by this type of research because the public is bombarded with these stories and they don't know what they're supposed to do."

The study's co-author stressed that no one should conclude that coffee is a "magic bullet."

"It's important to emphasize that by far the most important preventions are maintaining a healthy weight and exercising," said Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital.

The Centers for Disease Control and Prevention estimates that 18.2 million Americans, or more than six per cent of the population, have diabetes. Type 2 diabetes accounts for between 90 per cent and 95 per cent of the total.