An international research team from Australia, Canada and the US has found that men who drank two or more standard drinks of alcohol a day are more likely to develop prostate cancer.

The findings are in marked contrast to previous reviews that found inconclusive evidence of an association between alcohol use and incidence of prostate cancer.

The findings were put out by the National Drug Research Institute (NDRI) study, Alcohol Use and Prostate Cancer, where a meta-analysis was co-authored by Professor Kaye Fillmore and Dr. Alan Bostrom, from the University of California San Francisco (UCSF). Associate Professor Tanya Chikritzhs and Research Associate Richard Pascal, from the National Drug Research Institute (based at Curtin University of Technology in Western Australia); and Professor Tim Stockwell, director of the University of Victoria's Centre for Addictions Research of BC (CARBC). The study is published in Molecular Nutrition and Food Research.

The researchers reviewed 35 studies examining the relationship between level of drinking and the risk of developing prostate cancer. They found that some types of studies were more likely to find the relationship ("case control" studies) and others less likely ("cohort" studies), which explains different conclusions reached by other researchers.

When all types of studies were combined, however, the authors concluded: "Men who drink two or more standard drinks a day or 14 drinks a week or more have about a 20-per cent greater chance of developing prostate cancer."

What about protective effects? There is irony to the study findings. Much research has suggested that if middle aged and older men use alcohol at the rate of about 14 drinks a week this may prevent coronary heart disease, although recent evidence has suggested that the preventative power of alcohol may have been overstated.

In contrast, the new study finds that it is at about the same levels of drinking that alcohol use contributes to the incidence of prostate cancer. Taken together these findings emphasize the value for men to drink moderately. Men who drink two or more drinks a day might take this into account if they are consuming alcohol to prevent heart attacks.

"Further research is needed to examine more carefully the balance of health risks and benefits for different types of disease from drinking alcohol at different levels," the authors said.

In previous papers, the authors have also questioned the evidence supporting the view that moderate drinking protects against heart disease.

There has been scientific mystery surrounding the causes of prostate cancer. It is known that the rates differ across nations and men moving to another country tend to take on the rate of their adoptive country. This alone suggests that environmental factors play a role in the disease.

Except for age, race and family history, there is no consistent evidence for other factors (such as diet, smoking, exercise) to understand what factors might contribute to this serious form of cancer and how men might actively prevent it. The findings have been mixed or highly inconsistent for the role of alcohol in prostate cancer such that it is often concluded that alcohol use plays no role at all in its incidence.

Where to now? The study team suggests that future studies utilise multiple measurements because both the drinking habits and health status of men are rapidly changing with increasing age, making it difficult to ascertain the relationship between drinking and disease outcome.

Of considerable importance is the fact that many men with the disease are never diagnosed. This means findings from studies that do not determine if their control groups have the disease may be in serious doubt.

The NDRI study tested for the degree to which the available studies made efforts to be sure that their control or comparison groups did not have prostate cancer. Even among studies attempting to ascertain if these men had the disease, the positive association between alcohol use and prostate cancer remained. This finding gave the study team more confidence that the association between alcohol use and prostate cancer is valid.