The new findings confirm previous evidence of coffee's benefits, and although still not fully understood by researchers, would present a cheaper dietary intervention than many supplements and dietetic products marketed to reduce diabetes risk.
The study, conducted in Finland - the world's biggest per-capita consumer of coffee - men and women who drank at least 10 cups daily (the highest amount in the study) were 55 and 79 per cent less likely, respectively, to develop diabetes, compared with those drinking two cups or less each day.
Coffee is one of the world's largest traded commodities produced in more than 60 countries and generating more than US$70 billion in retail sales a year. But while incidence of diabetes is growing fast, up by a third during the 1990s due to the prevalence of obesity, relatively few studies have looked at the link between two.
In January, US researchers found evidence to show that intake of coffee or other caffeinated beverages protected against type 2 diabetes. Last year a Dutch team also identified an association between higher coffee consumption and lower risk for type 2 diabetes mellitus.
The new study, published in this week's Journal of the American Medical Association (291:1213-1219), is based on data from surveys conducted in 1982, 1987, and 1992 on 6974 men and 7655 women. The subjects were free of diabetes, heart disease, and stroke at the start of the study periods.
After an average follow-up of 12 years, the researchers from the National Public Health Institute in Helsinki identified 381 subjects with type 2 diabetes.
In both men and women, the risk of diabetes decreased as daily coffee intake increased although this trend was only statistically significant in women. The trend was not altered by age, smoking, weight, alcohol consumption or differences between filtered and nonfiltered coffee.
However the authors noted that there is still limited understanding of how the drink protects against diabetes. While initially thought to be related to caffeine, some studies suggest that other ingredients could be involved. 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.
The EU has provided funding for a project currently underway, 'Caffeine and Health', to investigate the benefits of coffee.