Small increase in breast cancer risk linked to moderate alcohol intake

Drinking small amounts of alcohol on a regular basis may increase a woman’s risk of breast cancer, according to a study published in the Journal of the American Medical Association.

Researchers followed the drinking habits of just under 106,000 women over 28 years.

The lifetime risk of developing breast cancer in the general population in the UK is one in eight. If we assume that this reflects moderate drinking (that is, between three and six glasses of wine a week) by many women, then the researchers found that the women in the study who drank no alcohol had a lower, one in nine, lifetime risk of breast cancer. They also found that the women who drank more heavily – at least two drinks a day – raised their risk to one in six.

The researchers also looked at the women’s drinking patterns. They found that women who drank large amounts of alcohol in one session (binge drinking) had a higher risk of developing breast cancer than those who drank small, regular amounts of alcohol.

They suggest that this increased risk of breast cancer may be related to the effect alcohol has on oestrogen levels in the body, though further studies are needed to investigate how this interaction may cause breast cancer.

Dr Prerna Sharma, Senior Physician, Bupa Health and Wellbeing UK, said: “The findings from this study suggest that even low levels of alcohol can contribute to an increase in a woman’s risk of breast cancer. Strictly speaking these results only apply to American nurses, but it seems likely there is a message here for us all.

“A limitation of this study is that it relied on the women accurately remembering their drinking habits from previous years; it's well documented that people commonly underestimate the amount they drink. Also, this study may be subject to the ‘well woman’ effect as all the women taking part were nurses so were likely to be more knowledgeable and engaged with healthy lifestyle habits. Therefore, these findings may not accurately reflect the general female population.

“Alcohol is known to have both harms and benefits to health, for example small amounts of alcohol are known to reduce cardiovascular disease. Women need to take a balanced approach to the findings of this study and weigh up the risks and benefits of alcohol to their own health. If you have any concerns about how alcohol affects your risk of breast cancer or cardiovascular disease, talk to your GP to help you decide what’s best for you.”

This type of study, an observational study, can never give concrete proof of cause and effect. There are many factors that influence a person's risk of developing breast cancer. These include the age at which menstruation started, the age at which a woman has her first baby and the age of menopause. Being overweight after the menopause as well as drinking alcohol can also increase a woman’s risk. Because breast cancer is common, many women have a relative with the disease. This isn’t an informative risk factor unless it was a woman with pre-menopausal breast cancer, a man with breast cancer, or families that have a history of both breast and ovarian cancer.

The study looked at women aged between 34 and 59 at the start of the study. All of them were American nurses who took part in a larger study called the Nurses’ Health Study. The women were followed up from 1980 to 2008 using questionnaires that asked about how much and how often the women drank and if their consumption of alcohol differed during different periods of their life.