Coffee and tea have been associated with a lower risk of developing diabetes, but little was known about how changes in levels of consumption affect the chances of developing the condition.
Research suggests that increasing your coffee intake by an average of one and a half cups a day – around 360ml – over a four-year period cuts your chances of developing type 2 diabetes by 11 per cent in the following four years.
Campaigners expressed doubts about the study.
The researchers, led by Frank Hu and Shilpa Bhupathiraju, at Harvard School of Public Health in Boston, based their findings on three major studies containing data on diet, lifestyle, medical conditions and chronic diseases over 20 years.
The studies involved regularly collecting information on changes in diet and health every two to four years.
The researchers, writing in the journal Diabetologia, said these repeated updates and the long duration of the studies allowed them to carefully check for changes in coffee intake and development of type 2 diabetes.
The final analysis included almost 100,000 women and just under 30,000 men.
The researchers discovered 7,269 cases of type 2 diabetes in the volunteers studied.
There was a link between coffee and the chances of the men and women developing the condition, which is linked to being overweight and normally develops in middle age.
Those participants who increased their coffee consumption by more than one cup a day – an average of 1.69 cups a day – over four years had an 11 per cent lower risk of type 2 diabetes in the subsequent four years compared to those who made no changes in their consumption.
Those who decreased their coffee intake by one cup a day or more – an average of two cups a day – had a 17 per cent higher risk of type 2 diabetes.
Changes in tea consumption were not linked to the risk of developing type 2 diabetes.
Those participants with highest coffee consumption and who maintained that – referred to as “high-stable consumers” since they drank three cups or more per day – had the lowest risk of type 2 diabetes.
Their risk of diabetes was 37 per cent lower than the “low-stable consumers” who drank one cup or less per day. However, the reasons behind the link between coffee consumption and type 2 diabetes remained unclear.
The researchers said that the higher risk linked to reduced coffee intake may represent a true change in someone’s risk, but could be due to the fact that people with medical conditions linked to diabetes, such as high blood pressure and cholesterol, may reduce their consumption after being diagnosed.
Dr Richard Elliott, research communications officer at Diabetes UK, said: “While this study found evidence of a connection between how much coffee you drink and your risk of Type 2 diabetes, this does not mean that increasing your coffee intake will reduce your diabetes risk.
“Even if people who drank more coffee did tend to have a lower risk of Type 2, it does not necessarily follow that coffee consumption was directly responsible.”