According to a meta-analysis of studies, individuals who drink more coffee (regular or decaffeinated) or tea appear to have a lower risk of developing type 2 diabetes. A previously published meta-analysis suggested drinking more coffee may be linked with a reduced risk, but the amount of available information has more than doubled since.

The researchers identified 18 studies involving 457,922 participants and assessing the association between coffee consumption and diabetes risk published between 1966 and 2009. Six studies involving 225,516 individuals also included information about decaffeinated coffee, whereas seven studies with 286,701 participants reported on tea consumption.

When the authors combined and analyzed the data, they found that each additional cup of coffee consumed in a day was associated with a 7 percent reduction in the excess risk of diabetes. Individuals who drank three to four cups per day had an approximately 25 percent lower risk than those who drank between zero and two cups per day.

In addition, in the studies that assessed decaffeinated coffee consumption, those who drank more than three to four cups per day had about a one-third lower risk of diabetes than those who drank none. Those who drank more than three to four cups of tea had a one-fifth lower risk than those who drank no tea.

"That the apparent protective effect of tea and coffee consumption appears to be independent of a number of potential confounding variables raises the possibility of direct biological effects," the authors write. Because of the association between decaffeinated coffee and diabetes risk, the association is unlikely to be solely related to caffeine. Other compounds in coffee and tea, including magnesium, antioxidants known as lignans or chlorogenic acids, may be involved, the authors note.

"If such beneficial effects were observed in interventional trials to be real, the implications for the millions of individuals who have diabetes mellitus, or who are at future risk of developing it, would be substantial," they conclude. "For example, the identification of the active components of these beverages would open up new therapeutic pathways for the primary prevention of diabetes mellitus. It could also be envisaged that we will advise our patients most at risk for diabetes mellitus to increase their consumption of tea and coffee in addition to increasing their levels of physical activity and weight loss."
References:
1. Rachel Huxley, et al. Coffee, Decaffeinated Coffee, and Tea Consumption in Relation to Incident Type 2 Diabetes Mellitus: A Systematic Review With Meta-analysis.  Arch Intern Med, Dec 14/28, 2009; 169: 2053 - 2063.