Although the coffee link is not fully understood - and with some evidence even seeming to contradict it - a proven link between coffee and a reduced risk of developing diabetes could present a cheaper dietary intervention to supplements and dietetic products marketed for the same effect.
In the UK alone, where 1.5 million people have been diagnosed with type 2 diabetes and an estimated million more have yet to be diagnosed, the disease has been said to account for five per cent of the annual National Health Service budget - around £10 million a day.
The World Health Organisation predicts that the number of people with type 2 diabetes will more than double over the next 25 years, linked to both the rise in ageing populations and the growing obesity problem.
For a study published in the August issue of the International Journal of Obesity, researchers at the University of New York and analysed data collected during the First National Health and Nutrition Examination Survey Epidemiologic Follow Up Study.
The study involved a total of 7006 subjects aged between 32 and 88 years, none of whom had a history of diabetes at the time they took part. Over the next 8.4 years, there were 301 reported cases of diabetes and eight diabetes deaths.
Across all the participants, the researchers observed a negative relationship between diabetes risk and consumption of ground coffee and regular tea.
This initial finding seemed to support the results of other recent research, including as study conducted in Finland and published in the Journal of the American Medical Association (291:1213-1219), which concluded that the risk of diabetes decreased as daily coffee intake increased in both men and women, although the trend was only statistically significant in women.
In this instance, the researcher said that the trend was not altered by age, smoking, weight, alcohol consumption or differences between filtered and nonfiltered coffee.
However when it came to age and weighloss, the New York researchers came to a different conclusion.
Looking at their data more closely, they noticed that the decrease in diabetes risk applied only to participants aged 60 years or younger. What is more, the positive relationship with consumption of ground caffeinated coffee, ground decaffeinated coffee and regular tea seemed only to apply to those who had previously lost weight.
No association was seen between diabetes risk and instant caffeinated coffee, instant decaffeinated coffee or herbal tea, leading the researchers to write: "Caffeine intake appeared to explain some, but not all, of the diabetes-risk reduction and weight change."
This is not the first time that scientists have suspected that caffeine is not the only ingredient involved. In 2003, researchers from the University of Surrey reported last year that another compound in coffee, chlorogenic acid, altered the glycaemic response in a small number of individuals tested.
Some studies have refuted benefits of caffeine or coffee for the diabetes-prone altogether, however. Canadian researchers reported in the March 2005 issue of Diabetes Care (vol 28, issue 3, pp 566-572) that caffeine was seen to significantly reduce insulin sensitivity in a small study. In another study published in the same journal last July, scientists from Duke University Medical Center in North Carolina suggested that drinking coffee could upset the body's ability to metabolise sugar.
An EU-funded project entitled 'Caffeine and Health' is currently underway to investigate the benefits of coffee.