The findings come from an analysis of almost 7,000 men from Italy - a country where coffee drinking is a culture.
It is quite normal for Italians to start the day with a cappuccino, followed by a caffè macchiato or two at lunch, and an espresso in the evening. In fact, the average Italian consumes around 600 cups of coffee every year, and this number is on the rise.
It seems, then, that there is no better population in which to study the effects of coffee consumption on the risk of prostate cancer.
Study co-author Licia Iacoviello, head of the Molecular and Nutritional Epidemiology Laboratory at I.R.C.C.S. Neuromed in Italy, and colleagues recently reported their findings in the International Journal of Cancer.
Gaining a 'clearer view' of the link between coffee and prostate cancer
Prostate cancer is the most common cancer among men in the United States, after skin cancer. According to the American Cancer Society, around 1 in 7 men will be diagnosed with the disease in their lifetime.
While a number of studies have suggested that coffee consumption may help to lower the risk of prostate cancer, others have found the opposite.
For their study, Iacoviello and colleagues further investigated the link between coffee intake and prostate cancer risk by analyzing the data of 6,989 men from Italy, aged 50 years or older, who were part of the Moli-Sani Project.
"In recent years we have seen a number of international studies on this issue," says first study author George Pounis, of the Department of Epidemiology and Prevention at I.R.C.C.S. Neuromed.
"But scientific evidence has been considered insufficient to draw conclusions. Moreover, in some cases results were contradictory. Our goal, therefore, was to increase knowledge in this field and to provide a clearer view."
As part of the study, participants were required to report their daily intake of Italian-style coffee using a food frequency questionnaire.
More than three cups of coffee daily lowered prostate cancer risk
Over an average of 4 years of follow-up, around 100 new cases of prostate cancer were identified among the men.
The researchers found that men who consumed at least three cups of Italian-style coffee every day were at a 53 percent lower risk of developing prostate cancer, compared with men who consumed fewer than three cups daily.
To confirm the anti-cancer effects of coffee, the team tested extracts of caffeinated and decaffeinated Italian-style coffee on prostate cancer cells in the laboratory.
They found that the caffeinated coffee extracts reduced the proliferation of cancer cells - that is, the ability to grow and divide - and decreased their ability to metastasize, or spread. These effects were almost non-existent with decaffeinated coffee extracts.
"The observations on cancer cells allow us to say that the beneficial effect observed among the 7,000 participants is most likely due to caffeine, rather than to the many other substances contained in coffee," notes study co-author Maria Benedetta Donati, also of the Department of Epidemiology and Prevention.
However, the researchers point out that the study was conducted on an Italian population with a strong coffee culture, which is characterized not only by the amount of coffee that is consumed, but also by the way in which it is made.
"They prepare coffee [the] rigorously Italian way: high pressure, very high water temperature, and with no filters," says Iacoviello. "This method, different from those followed in other areas of the world, could lead to a higher concentration of bioactive substances."
"It will be very interesting, now, to explore this aspect. Coffee is an integral part of Italian lifestyle, which, we must remember, is not made just by individual foods, but also by the specific way they are prepared."