Numerous studies of coffee's links to myriad diseases have provided head-spinning results, but a new paper finds coffee drinkers have no more risk of illnesses such as heart disease or cancer.
In fact, they are less likely to end up with type 2 diabetes, the form of the disease that does not require insulin and is linked to obesity.
"We do not encourage people to start drinking coffee if they do not enjoy this, but the overall evidence on coffee and health suggests that there is no reason for persons without specific health conditions to reduce their coffee consumption in order to reduce their risk of chronic diseases," said Rob van Dam, a professor at National University of Singapore, who was not involved in this study.
In some cases, coffee drinking has been tied to an increase in heart disease, cancer, stroke and more. In other cases, coffee drinking appears benign or even linked to better outcomes.
Coffee's effect on chronic diseaase
"There have been conflicting results from previous studies regarding coffee's effect on chronic disease risk depending on the type of disease," said Anna Floegel, the lead author of the study and an epidemiologist at the German Institute of Human Nutrition Potsdam-Rehbruecke. "That is why we decided to look at different diseases at the same time to estimate the overall health effect of coffee consumption."
The researchers, who published their findings in the American Journal of Clinical Nutrition, collected information at the beginning of the study on coffee drinking habits, diet, exercise and health from more than 42,000 German adults without any chronic conditions.
For the next nine years, the team followed up on the participants every two or three years to see whether they developed any health problems.
Coffee drinkers likely to develop heart attack
In particular, Floegel's group looked for cases of cardiovascular disease, stroke, heart attack, diabetes and cancer.
They found that coffee drinkers and non-drinkers were similarly likely to develop one of these illnesses.
For instance, 871 out of 8,689 non-drinkers developed a chronic disease, compared to 1,124 out of 12,137 people who drank more than four cups of caffeinated coffee a day – about 10% in both groups.
"Our results suggest that coffee consumption is not harmful for healthy adults in respect of risk of major chronic diseases," Floegel told Reuters Health by email.
Diabetes less likely with drinking coffee
On the other hand, Floegel's team found that coffee drinkers were less likely to develop type 2 diabetes than those who didn't drink coffee.
Among those who guzzled four cups a day, 3.2% later reported that they had type 2 diabetes, compared to 3.6% of people who drank no coffee.
After taking into account factors that could influence diabetes, such as weight and smoking, the researchers determined that frequent coffee drinkers were 23% less likely to develop diabetes.
That squares with other studies.
"Higher coffee consumption has been consistently associated with a lower risk of type 2 diabetes in many prospective studies across the world," van Dam said by email (see Reuters Health report of December 14, 2009).
De-caffeinated coffee has similar effect
This doesn't mean that coffee is responsible for preventing type 2 diabetes. The researchers tried to account for other known diabetes-influencing factors, but there could be inaccuracies in measuring these factors and there could be other, unknown influences too, van Dam said.
However, experiments in animals have hinted that certain chemicals found within coffee could positively affect metabolism, he noted.
The most notorious component of coffee – caffeine – is likely uninvolved, because Floegel's group found that frequent decaf drinkers also had a lower risk of developing diabetes than people who didn't drink any coffee.
Floegel said she'd like to see future studies dig down into the possible biological explanations for coffee's role in diabetes, and how people who already have diabetes respond to coffee.
(Kerry Grens, Reuters Health, March 2012)
Type 2 diabetes