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Coffee (caffeine) and diabetes – is it good or bad?

coffee and diabetes

The average UK citizen consumes caffeine everyday, whether it’s from coffee, tea, chocolate or fizzy drinks. For most people this is a harmless energy boost but for those with type 2 diabetes their blood sugar may end up increasing. Type 2 diabetes mellitus is a major health problem associated with increased morbidity and mortality that is prevalent in developed countries and cases will only increase in coming years.

The evidence for whether caffeine is bad for those with diabetes is confusing at best. Studies carried out have shown caffeine to be beneficial, harmful and neutral for those with type 2 diabetes. This is because coffee contains different chemicals, some of which have beneficial effects whereas others give more harmful effects.

Caffeine’s positives

Some studies suggest that drinking coffee may actually reduce your risk of developing type 2 diabetes. Coffee contains polyphenols and its anti-oxidant properties are believed to help prevent inflammatory illnesses such as type 2 diabetes. Coffee also contains the minerals magnesium and chromium. Increasing magnesium intake has been linked to lower rates of type 2 diabetes.

Increases in consumption of coffee and caffeinated substances in one study led to a decrease in the risk of diabetes. Age-stratified analysis showed this decrease in risk only applied to subjects under the age of 60. (1) In another study the risk of type 2 diabetes decreased by 6% for each cup per day increase in coffee consumption. (2) A study by the Harvard School of Public Health also found that those who decreased their coffee consumption by more than one cup per day increased their chance of developing type 2 diabetes by 17%.

Caffeine’s negatives

If you already have type 2 diabetes, caffeine may impact insulin action and increase your blood sugar. One study looked at people with type 2 diabetes who took a 250-milligram caffeine pill at breakfast and another at lunchtime. The result was that their blood sugar with 8% higher than on days when they didn’t consume caffeine. One small study showed that just one serving of coffee could have a negative impact on blood sugar control in healthy but overweight men. (3) Caffeine may lower insulin sensitivity so cells in the body don’t react as much to the hormone and don’t absorb as much sugar from your blood after you eat or drink.

Caffeine is thought to have this effect because caffeine raises epinephrine which can prevent your cells from processing as much sugar. It also blocks adenosine which plays a role in how much insulin your body makes and can reduce sleep which may lower insulin sensitivity.

Many coffees now a days contain sugar and syrups that can be problematic for those with diabetes or at risk of diabetes. These sugary drinks dramatically increase blood sugar levels.

Decaffeinated coffee

Whilst caffeine may alter insulin sensitivity, other properties of coffee are beneficial. Therefore, it is believed that decaffeinated coffee may be the best option for those with type 2 diabetes as this includes mainly the positives of coffee.

Water is the best drink for those with diabetes and this should be coupled with a healthy diet and plenty of exercise.


  1. Greenberg JA, Axen KV, Schnoll R & Boozer CN. Coffee, tea and diabetes: the role of weight loss and caffeine. International Journal of Obesity. 2005
  2. Carlstrom M, Larsson SC. Coffee consumption and reduced risk of developing type 2 diabetes: a systematic review with meta-analysis. Nutritin Reviews. 2018
  3. Robertson TM, Clifford MN et al. A single serving of caffeinated coffee impairs postprandial glucose metabolism in overweight men. 2005.