A recent study of over one million middle-aged women suggests that drinking even small amounts of alcohol increases the risk of developing cancer. While not definitive, this UK study is highly troubling.

The Million Women Study was designed to test the correlation between alcohol and cancer in women. It found that any alcohol consumption increased the subjects' risk of contracting cancer over the next seven years. The more alcohol was consumed, the higher the cancer risk. The type of alcohol that was consumed — beer, wine, liquor — made no difference. On average, the women in the study who drank consumed one drink per day; very few had three or more drinks.

The increase found was 15 additional cancers per thousand women per drink per day. Over three-quarters of these additional cancers were breast cancers. Estimating from the nationwide cancer rate, the researchers suggest that alcohol could be the cause of 13% of the total cases of cancer of the breast, liver, rectum and upper aero-digestive tract found in the UK.

The study shows that the subjects who drank alcohol had an increased risk of cancer. As a correlational study, it can't prove that the alcohol itself caused the cancers, though that's the most obvious explanation. It's possible that some other shared behavior, trait or exposure of the drinkers was the actual cause.

In an editorial that accompanied the publication of this study, the editorialists comment that this should give pause to those who have been noticing that some studies suggest a cardiovascular benefit from alcohol. The cancer risk suggested by this study may very well outweigh any CV benefit. In the words of the editorialists, "There is no level of alcohol consumption that can be considered safe."

The study was of 1,280,296 women who attended breast cancer screening clinics in the UK between 1996 and 2001. Information on alcohol consumption was obtained from questionnaires. The number of cancers that the participants developed over the next seven years was then compared to their drinking behavior.

Both the results of the Million Women Study and the accompanying editorial appear in the March 4, 2009 issue of the Journal of the National Cancer Institute.