A 20-year study by Harvard University has concluded that men who drink a lot of coffee are less likely to develop prostate cancer.

The study, which focussed on a group of 50,000 men, found that those who drank six or more cups of coffee per day were 20% less like to contract prostate cancer than those who didn't drink coffee. More significantly, they were also 60% less likely to die from the disease. Closer investigation of the results revealed that decaffeinated coffee was just as effective in protecting against the disease.

The men's diets were examined every five years between 1986 and 2006. During this time, more than 5,000 of the men went on to develop prostate cancer, of which 642 cases were expected to be fatal. However, in those who drank as little as one cup of coffee, there was a significantly lower incidence of fatal prostate cancer. The greater the amount of coffee consumed daily, the more pronounced the protective effect was.

The researchers believe that antioxidants, such as phenolic acid, in coffee may be responsible for the protective effect. These substances can alter the concentration of sex hormones in the body, regulate blood sugar and have an anti-inflammatory effect, which can all help protect again prostate cancer.

One of the researchers, Kathryn Wilson, said: ''If our findings are validated, coffee could represent one modifiable factor that may lower the risk of developing the most harmful form of prostate cancer.''

However, she also emphasised that people shouldn't change their coffee drinking habits based on this research alone. Clearly, there are many different types of coffee and ways of preparing it. These variables may influence the level of protection derived from the coffee. What's more, excessive caffeine intake associated with drinking too much coffee can be harmful.

Certainly, more research needs to be done, but this could be another addition to a growing list of ways in which the humble coffee bean may protect against human disease. Previous studies have suggested that coffee can reduce blood pressure, protect against breast and skin cancer, prevent the onset of Alzheimer's and even reduce the risk of alcoholic liver damage.