"Even relatively low levels of drinking - on the order of one alcoholic drink per day - increase a woman's risk of developing cancer," says lead researcher Naomi Allen, at University of Oxford in the United Kingdom.
"Because a high proportion of women drink low amounts of alcohol regularly and because most of the increased risk is for breast cancer, the risk among women associated with drinking alcohol is of particular importance."
In fact, the study found that moderate drinking accounts for 13 percent of breast, liver, rectum, and upper respiratory/digestive tract cancers among women.
Linked Most Highly with Breast Cancer
The link between moderate alcohol intake and breast cancer in women is well-known, the researchers point out.
What is new here, they say, is the finding that even low levels of drinking can raise a woman's risk of developing cancer of the liver and rectum. For women who smoke, cancers of the mouth and throat were also linked to high alcohol consumption.
For the study, Allen's team collected data on more than 1.2 million middle-age British women participating in the Million Women Study. The researchers used the National Health Service Central Registries to identify cancer cases among these women.
Most women in the study had about a drink a day, and a smaller percentage had three or more drinks a day. Follow-up studies, after more than a seven year period, revealed 68,775 women developed cancer.
"These findings are robust, and alcohol consumption was assessed several times before women were diagnosed with cancer, making these estimates reliable," says Allen.
Overall, the risk of cancer increased as alcohol consumption increased. The type of alcohol consumed appeared to make no difference.
Women who drank and also smoked faced increased risk of cancers of the oral cavity and pharynx, esophagus, and larynx (voice box), the researchers reveal.
The study suggests "that in developed countries, where women typically consume low-moderate amounts of alcohol, we estimate that for every additional drink regularly consumed each day, there would be about 15 extra cases of cancers of the breast, liver, rectum, and mouth and throat diagnosed for every 1,000 women up to the age of 75," says Allen. "Most of this excess risk is due to breast cancer."
Susan M. Gapstur, Ph.D, vice president of epidemiology at the American Cancer Society (ACS), says the findings confirm and expand on those from previous studies in men and in smaller studies of women.
But several questions remain unanswered, she notes.
"For example, researchers remain concerned about the pattern of consumption," says Dr. Gapstur. "It is unclear, for example, whether someone who drinks several glasses of wine on one day during the week has the same risk as someone who drinks one glass of wine per day with a meal. In addition, the effects of quitting or reducing drinking on cancer risk are also unclear."
Discuss Risk and Benefit with Physician
The American Cancer Society currently recommends limiting intake to one drink a day for women and two drinks a day for men, says Dr. Gapstur.
On the other hand, numerous studies have suggested that alcohol, especially red wine, might help deter heart disease - complicating decisions around drinking and health.
"If you do not drink, there is no reason to start drinking," reasons Dr. Gapstur. "However, in light of the findings from the Million Women Study, women who are concerned about their cancer risk versus their risk of cardiovascular disease might want to discuss the potential risks and benefits of even low alcohol intake with their health-care providers."
In an accompanying journal editorial, Dr. Michael Lauer, director of the Division of Prevention and Population Sciences at the US National Heart, Lung and Blood Institute, says he believes the risk for cancer might outweigh any perceived benefit in terms of heart disease.
"People who are not drinkers should not start drinking to prevent heart disease, and even people who are drinking should discuss this with their physicians," he says. "And as part of that conversation, they should consider other conditions than heart disease. We cannot just focus on heart disease."
Always consult your physician for more information.