Among more than 100,000 men and women followed for 22 years, those who drank sugar-sweetened drinks were as much as 23% more likely to develop diabetes than those who didn’t, but the risk was about the same whether the drinks contained caffeine or not. And drinkers of both caffeinated coffee and decaf had slightly lowered diabetes risk.
Lead author Dr. Frank Hu of Harvard University stated that, "We found that caffeine doesn’t make a difference at all." "Coffee can be beneficial and the caffeine doesn’t appear to have a positive or negative effect on diabetes risk."
Dr. Hu and his coauthors wanted to know if people who regularly drink sugary and caffeinated beverages might only be exaggerating their risk of developing diabetes. They examined the health habits of 75,000 women and 39,000 men involved in long-term health studies that began in the mid-1980s.
Compared to people who didn’t consume sugary drinks, the likelihood of developing diabetes over the years for those who did was higher by 13% (caffeinated) or 11% (decaffeinated) among women, and by 16% (caffeinated) or 23% (decaffeinated) among men.
Caffeine-free artificially sweetened drinks were also linked to a slight (6%) increase in risk among women.
However, coffee drinkers showed slightly lower risk compared to non-drinkers. The chances of developing diabetes were 8% lower among women, whether they drank decaf or regular coffee, and for men, 4% lower with caffeinated coffee and 7% lower with decaf.
Dr. Hu and his team have used this same dataset, which contains the health habits of mostly white health professionals, to suggest that regular coffee drinking in general is tied to lower diabetes risk.
But past studies, like the current one, have also found that the risk falls even lower if adults drink decaffeinated coffee.
"Our understanding of the body’s tolerance to caffeine is not complete," said Dr. James Lane of Duke University. Dr. Lane has done short-term studies that linked caffeine to a disruption of the body’s ability to process glucose.
This latest study suggests that people who currently drink sugary beverages could substitute unsweetened coffee or tea – though tea was associated with fewer benefits – instead.
Dr. Lane added that, "I’m disappointed that they are essentially repeating something they published several years ago. The bit about including sugar sweetened beverages and caffeine’s possible interaction with sugar and diabetes does not add something of great value."
Others agree more research is necessary to untangle caffeinated coffee’s complicated relationship with diabetes risk.
At least one small, randomized two-month-long trial led last year by Dr. Rob Martinus van Dam of the National University of Singapore, also a co-author of the current study, found that caffeinated coffee did not seem to affect glucose levels in the blood.
Am. J. Clin. Nutrit. 2012