Drinking caffeinated coffee was found to reduce the risk of developing type 2 diabetes by as much as 60% in a newly published study that included people at high risk for the disease.
Even those who used to drink coffee but quit were less likely to develop diabetes than those who never drank it.
The new study was published in the November issue of the journal Diabetes Care.
"Our findings were very strong," researcher Besa Smith, MPH, tells WebMD. "The next step is to pinpoint the compounds in coffee responsible for this protective effect."
The new research is not the first to find that coffee drinkers have an edge in terms of protection from diabetes.
A Finnish study, reported in 2004, suggested a 30% reduction in type 2 diabetes risk among people who drank three or four cups of coffee a day. Women in the study who drank 10 or more cups a day showed a 79% reduction in risk.
And combined results from 15 studies involving more than 200,000 participants suggested a similar protective effect. People who drank the most coffee had the lowest diabetes risk in the review, conducted by researchers from the Harvard School of Public Health.
A Unique Study
The study by Smith and colleagues from the University of California San Diego was unique because it included people at high risk for type 2 diabetes whose blood sugar levels were higher than normal.
The condition, known as impaired glucose tolerance, is considered a strong predictor of diabetes.
A total of 910 adults were followed for an average of eight years after an assessment of their coffee drinking habits was conducted. The average age of the participants was 66; 41% were men.
After adjusting for other known diabetes risk factors, the researchers concluded that both past and current drinkers of caffeinated coffee had about a 60% reduction in diabetes risk, compared with study participants who never drank coffee.
A similar reduction in risk was seen among the roughly one-third of study participants with impaired glucose tolerance.
The researchers did not exclude people who drank decaffeinated coffee from the study, but too few participated to draw conclusions.
Searching for a Reason
It is not clear how coffee affects diabetes risk, but Smith says the benefits are probably not due to caffeine.
"It appears that there are other compounds in coffee responsible for this," she says.
Studies are needed to isolate the component or components responsible for the protective effect against diabetes, Smith says.
She adds that it is premature to recommend coffee drinking as a public health strategy for lowering the risk of diabetes.
American Diabetes Association spokesman Larry Deeb, MD, agrees. But he says there is little evidence that drinking coffee is bad for people with diabetes.
Deeb directs the diabetes center at Tallahassee Memorial HealthCare hospital; he is president of medicine and science for the American Diabetes Association.
"People with diabetes and those at risk for developing diabetes have enough to worry about," Deeb tells WebMD. "It is nice to know that coffee isn't one of them, and it may actually help lower risk."
SOURCES: Smith, B. Diabetes Care, November 2006; vol 29: pp 2385-2390. Besa Smith, MPH, biostatistician, division of epidemiology, department of family and preventive medicine, University of California, San Diego, La Jolla, Calif. WebMD Medical News: "Drinking Lots of Coffee May Prevent Diabetes." WebMD Medical News: "Coffee May Cut Type 2 Diabetes Risk."
By Salynn Boyles
Reviewed by Louise Chang