Men who enjoy their morning cup of coffee can drink a little easier. A new research review finds that java lovers appear no more likely to develop prostate cancer than other men.

In an analysis of a dozen studies on coffee intake and prostate cancer risk, researchers found no strong evidence linking the beverage to either an increased or decreased risk of the disease.

The findings, published in the medical journal BJU International, add to the conflicting body of research on coffee and cancer risk.

A number of studies have found connections between regular coffee consumption and certain cancers - a decreased risk in some cases, and an increased risk in others. A study published last month, for example, found that coffee drinkers had a lower risk of head and neck cancers than non-drinkers did, with the risk declining as coffee consumption rose.

Studies on prostate cancer have come to conflicting conclusions, with some linking greater coffee consumption to a heightened risk of the cancer and others showing no relationship between the two.

To investigate further, researchers led by Dr. Chang-Hae Park, of the National Cancer Center in Goyang, South Korea, pooled the results of 12 previous studies on coffee intake and prostate cancer risk.

Overall, they found no strong relationship between men’s reported coffee-drinking habits and their risk of prostate cancer.

According to the researchers, the discrepancies among past studies on coffee and prostate cancer risk may be explained by the studies’ designs.

Of the studies the researchers reviewed, eight were what are known as case-control studies, where people with a disease are compared with similar individuals - typically of the same age and sex - who are free of the disease.

Those types of studies have a number of limitations, including the fact that participants are asked to recall their past lifestyle habits.

So, for example, because coffee drinking is often seen as a less-than- healthy habit, prostate cancer patients may recall their consumption as being greater than it actually was. Healthy study participants, on the other hand, may have an overly rosy view of their lifestyle habits.

When Park’s team looked only at the case-control studies, there was an association between greater coffee intake and higher prostate cancer risk. However, the same was not true of the remaining four studies, which were what are known as cohort studies.

In those studies, men initially free of prostate cancer were asked about their coffee-drinking habits, then followed over time to see which ones developed prostate cancer. That type of study produces stronger evidence of a link, or lack thereof, between an “exposure” - in this case, coffee intake - and a disease risk than a case-control study can.

Because the cohort studies in this review showed no connection between coffee and prostate cancer, Park’s team concludes that “there is no evidence to support a harmful effect of coffee consumption on prostate cancer risk.”

Still, it is plausible, based on lab research, that coffee could have both positive and negative effects on the risks of some cancers, Park’s team points out. Animal research suggests, for example, that caffeine can either suppress or stimulate tumors, depending on which animal species is studied and the point in the cancer process at which the caffeine is administered.

In addition to caffeine, coffee contains more than one thousand chemicals, some of which appear to have antioxidant effects that could help protect cells from damage that can lead to cancer.

However, exactly how all those chemicals interact in the human body, and whether coffee has real effects on the risks of various cancers, remains unclear.

SOURCE:  BJU International, online June 30, 2010.