Drinking decaffeinated coffee is associated with a lower risk of developing diabetes, research suggests.
Drinking decaf coffee may reduce risk of diabetes
A large US study of 28,000 women found that more than six cups of decaf coffee a day was linked with a 33% lower risk of diabetes compared with no coffee.
There was a much smaller reduced risk in women who drank caffeinated coffee.
The 11-year-long study in Archives of Internal Medicine suggests that in contrast to other research, caffeine intake does not reduce diabetes risk.
The researchers from the School of Public Health at the University of Minnesota analysed data from postmenopausal women who took part in the Iowa women's health study between 1986 and 1997.
At the beginning of the study none of the women had diabetes or cardiovascular disease.
Coffee consumption was ascertained with a series of questionnaires and women were also asked about their risk factors for diabetes, including age, body mass index, physical activity, alcohol consumption and smoking history.
Taking into account the other factors, compared with non-coffee drinkers, women who had six cups of coffee a day had a 22% reduced risk of developing diabetes.
But when the researchers analysed the data for women who drank decaffeinated and caffeinated coffee separately they found the risk reduction was 'considerably' greater in the decaf group and they concluded that caffeine was not causing the reduction in diabetes.
The link appeared to be the same across different body weights and ages.
They also looked to see if some other ingredients in decaffeinated coffee could be responsible.
Minerals found in coffee such as magnesium and phytic acid may benefit blood sugar control but the researchers could not find a link using the data they had.
Coffee also contains a number of phytochemicals, which appear to have high antioxidant activity which the researchers suggested could protect cells that produce insulin in the pancreas against damage, preventing or delaying diabetes
Study leader, Dr Mark Pereira, associate professor at the University of Minnesota School of Public Health said: "Other studies, suggested that caffeine may be one of the protective factors. Our study contradicts those findings.
"Caffeine may have some beneficial effects on metabolism in moderate or high doses, but it may also have some deleterious effects which could offset the benefit.
"Maybe that is why we don't see an association with diabetes in our study.
He added: "I think one of the key things with coffee is that high intakes are so common in the population.
"If people consumed that much tea or fruits and vegetables we may see stronger associations with these other dietary factors and diabetes risk."
"There appears to be great potential for coffee to help reduce the risk of diabetes. Identifying the mechanism responsible for this should definitely be the subject of further research."
Roopinder Brar, Care Advisor for Diabetes UK said: "The results of this study are interesting, however, more research needs to be done to determine which ingredient of de-caffeinated coffee may be responsible for a reduced diabetes risk.
"Drinking more than six cups of coffee a day could have other, less beneficial side effects, for example, causing dehydration.
"If people really want to reduce the risk of developing diabetes then regular exercise and a healthy diet have been shown to be a much safer and reliable bet."