A review of prospective studies of regular or decaffeinated coffee and tea revealed that for each additional daily cup of coffee was associated with a 7 per cent reduction in the excess risk of diabetes, according to findings published in the Archives of Internal Medicine.
“If such beneficial effects were observed in interventional trials to be real, the implications for the millions of individuals who have diabetes mellitus, or who are at future risk of developing it, would be substantial,” wrote the reviewers, led by Rachel Huxley from the University of Sydney, Australia.
Benefits of the bean
The beverage, and its constituent ingredients, has come under increasing study with research linking it to reduced risk of diabetes, and improved liver health.
Coffee, one of the world's largest traded commodities produced in more than 60 countries and generating more than $70bn in retail sales a year, continues to spawn research and interest, and has been linked to reduced risks of certain diseases, especially of the liver and diabetes.
The new review reinforces the link between coffee consumption and a reduced risk of developing diabetes, a condition that affects an estimated 19 million people in Europe, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are almost 24 million people with diabetes, equal to 8 per cent of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.
Huxley and her co-workers reviewed data of over 500,000 individuals with over 21,000 cases of type-2 diabetes from prospective studies. Eighteen studies looked at coffee, six studies also included information about decaffeinated coffee, and seven studies reported on tea consumption.
In addition to risk-lowering effects of additional regular coffee consumption, three to four cups of decaffeinated coffee were associated with a 33 per cent lower risk of diabetes, compared to drinking no decaf.
Tea drinkers also benefited, with three to four cups associated with a one-fifth lower risk, added the researchers.
“That the apparent protective effect of tea and coffee consumption appears to be independent of a number of potential confounding variables raises the possibility of direct biological effects,” wrote the reviewers.
Commenting on the possible bioactives and mechanism of action, Huxley and her co-workers noted that because of risk reductions associated with decaffeinated coffee, the effects were unlikely to be due solely to caffeine. Other compounds in coffee and tea, such as magnesium, antioxidant lignans or chlorogenic acids, may be involved.
“The identification of the active components of these beverages would open up new therapeutic pathways for the primary prevention of diabetes mellitus,” wrote the researchers.
“It could also be envisaged that we will advise our patients most at risk for diabetes mellitus to increase their consumption of tea and coffee in addition to increasing their levels of physical activity and weight loss,” they concluded.
Cautious and careful
Commenting independently on the results,Professor Lars Ryden, a diabetes specialist and spokesperson for the European Society of Cardiology, said: "This is a cautiously and carefully conducted meta-analysis which means authors have carefully conducted studies although each are too small to give an answer to the question although they indicate a positive correlation between the consumption of coffee and a decreasing occurrence of diabetes. So the principle is that if you drink coffee whether it is decaffeinated or not, you have less chance of developing diabetes. The data has been strengthened by bringing several studies together.
"There are sometimes claims that coffee may do harm, that it may increase the propensity to Cardiovascular disease, but there is no evidence for this. The message is that people may drink coffee safely. Coffee from this point of view may actually be of benefit, as well as reducing the risk of getting diabetes – although the reduction is small (around 7 per cent).
"It is interesting to consider why a beverage like coffee has a beneficial effect. It is obviously not the caffeine as decaffeinated coffee has the same efficiency as caffeinated coffee. Coffee may contain antioxidants but the studies have not measured the number of chemicals in the blood which is important,” added Prof Ryden.
Source: Archives of Internal Medicine
Volume 169, Issue 22, Pages 2053-2063
“Coffee, Decaffeinated Coffee, and Tea Consumption in Relation to Incident Type 2 Diabetes Mellitus: A Systematic Review With Meta-analysis”
Authors: R. Huxley, C.M.Y. Lee, F. Barzi, L. Timmermeister, S. Czernichow, V. Perkovic, D.E. Grobbee, D. Batty, M. Woodward