Does boiled coffee protect against type 2 diabetes?


Illustration photo

The study examined the association between consumption of boiled coffee and filter coffee at ages 40-45 and the development of type 2 diabetes at ages 45-60.

Several studies have found a beneficial relationship between coffee consumption and type 2 diabetes, but this is the first time such a large study has looked at this association.

“This study found that the risk of developing type 2 diabetes decreased with increasing coffee consumption in approximately the same degree for boiled and filtered coffee,” said researcher Vidar Hjellvik at the Norwegian Institute of Public Health.

Those who drank nine cups of boiled coffee or more had a 35 per cent lower risk of developing type 2 diabetes than those with the same age, body mass index, smoking habits, education, and physical activity levels who drank less than one cup daily. For those who drank the equivalent amount of filter coffee, there was a risk reduction of 38 per cent.

360 000 women and men

The study used information about coffee consumption by 360 000 diabetes-free women and men from health studies conducted between 1985 and 1999. By linking with the Norwegian Prescription Database at the Norwegian Institute of Public Health, one could identify how many people used medicines for type 2 diabetes in the period 2004-2007 (blood glucose-lowering medicines, e.g. insulin; ATC group A10B).

Many people with type 2 diabetes control the disease with just diet and exercise and these were not captured in this study. It is assumed that the proportion that needed medicine among the diagnosed diabetics in the follow-up period was independent of coffee consumption. It also cannot be ruled out that other factors associated with coffee drinking than those taken into account in the study influenced the development of type 2 diabetes.

How much coffee is recommended?

The majority of people are not recommended to drink nine cups of coffee a day.

”Everyone is different and can tolerate varying amounts of caffeine. Some can drink 30 cups a day while most people stick to one or two cups. This is partly to do with genes. We have different abilities to metabolise caffeine in the body and those who convert it slowly can tolerate less. If everyone drank four to five cups of coffee per day, we would probably end up with a whole host of other problems, such as insomnia“ said Helle Margrete Meltzer, Department Director at the Norwegian Institute of Public Health.

”Each of us usually knows how much we can tolerate,” says Meltzer. “Most people notice when they cross their own threshold. They recognise the restlessness, anxiety, palpitations and nervousness.

Moreover, when it comes to boiled coffee, several previous studies have shown that it increases cholesterol levels and may cause increased risk of cardiovascular diseases.”


Caffeine (chemical name: trimetyl-xanthine) occurs naturally in several plants. Coffee, guarana and tea bushes contain very high concentrations and are therefore used in caffeinated drinks like coffee, tea, cola and energy drinks.

Caffeine affects many functions in the body, including the central nervous system (stimulation, insomnia), heart (increase in pulse rate), kidney function (increased urine production), blood circulation, as well as stomach, bowel, and lung function. Early symptoms of acute poisoning can already be observed at 500 to 600 mg caffeine per day, equivalent to 5 to 6 cups of coffee, and are characterised by headaches, nausea, stomach cramps, restlessness, rapid pulse and irregular heart rhythm. A lethal dose of caffeine is about 8 to 10 grams / day, equivalent to approximately 60 to 100 cups of coffee.


Hjellvik V, Tverdal A, Strøm H. Boiled Coffee Intake and Subsequent Risk for Type 2 Diabetes. Epidemiology, Vol. 22, Number 3: 418-21