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Does coffee and tea hold the key to preventing diabetes?

17 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.

Coffee cup

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 Sneh Khemka, medical director for Bupa Global, commented: “This study does not provide the solution to the global diabetes crisis. The figures look impressive, but in terms of reducing your actual risk, they do not take into account a person’s likelihood of developing the condition within their lifetime (absolute risk).

“Secondly, the studies analysed mainly focused on white, Western populations. We know that ethnic groups are affected differently by type 2 diabetes. These findings cannot be applied to the population worldwide. Finally, none of the studies took into account diet or lifestyle factors. We cannot be sure if the effects seen in this study were really down to drinking tea or coffee, or if they were the result of some other factor or behaviour.

“It is estimated that by 2025, 380 million people worldwide will be affected by type 2 diabetes. Clearly action needs to be taken to avert this health crisis. The best way you can reduce your risk is to eat a healthy diet, maintain a healthy weight and take plenty of exercise – at least 30 minutes on most days of the week.”

Key facts

  • More than 220 million people worldwide have diabetes.
  • Type 2 diabetes is a lifelong condition in which the body is unable to regulate the amount of glucose in the blood properly. It develops when the body does not respond to the natural hormone insulin.
  • You are more likely to develop type 2 diabetes if:
    • 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
  • Some people can control their condition by making lifestyle changes. For others, medicines or insulin injections may be prescribed.
  • Read the study

    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.