19 December 2009
Drinking coffee, decaffeinated coffee and tea may lower your risk of developing type 2 diabetes, according to a new systematic review of the evidence.
This research does not mean that everyone should increase the amount of tea and coffee they drink. The figures are not generalisable to everyone worldwide.
Previous research has suggested that drinking lots of coffee reduces your chances of developing diabetes, but this latest review has looked at all the evidence produced over the last few decades to try to establish how effective it is.
The researchers analysed the results of 18 well-conducted studies involving almost 450,000 people. Eleven of the studies also included information about how much decaffeinated coffee and tea (including green and black tea) people drank. The researchers looked at these results as well to see if the same effect could be seen.
They found that people who drank three to four cups of coffee per day were a quarter less likely to develop type 2 diabetes than those who drank none or fewer than two cups of coffee a day. And for every additional cup of coffee drunk, there was a seven percent reduction in a person's risk of developing type 2 diabetes.
For people who had decaffeinated coffee , they found that having three to four cups a day reduced their risk of developing type 2 diabetes by a third when compared with non-decaf drinkers. For people drinking three to four cups of tea, their risk was reduced by a fifth when compared with non-tea drinkers.
According to the researchers, these findings show that the protective effect of coffee and tea is unlikely to be solely down to caffeine, rather due to a combination of chemicals in these drinks, such as magnesium and antioxidants (lignans and chlorogenic). It is thought that these chemicals increase insulin sensitivity in the body, preventing a build up of glucose in the bloodstream. When there is too much glucose in the bloodstream, the body is unable to produce enough insulin to cope, leading to type 2 diabetes. However, the studies the researchers looked at did not measure levels of glucose or insulin sensitivity in the body so they are only able to speculate on this.
Dr Annabel Bentley, assistant medical director for Bupa, commented: "This research does not mean that everyone should increase the amount of tea and coffee they drink. The figures are not generalisable to everyone worldwide.
"The best way to reduce your risk of type 2 diabetes is by maintaining a healthy weight, taking plenty of exercise and eating a healthy, balanced diet."
- you are overweight or obese
- you do not exercise very often
- type 2 diabetes runs in your family
- you smoke
- you drink alcohol excessively
- you are of African-Caribbean, South-Asian or Hispanic origin
Huxley R, Ying Lee CM, Barzi F, 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. 2009;169(22):2053-2063. http://archinte.ama-assn.org/cgi/content/short/169/22/2053?home