A new study links alcohol consumption with an increased risk of the most common form of breast cancer in postmenopausal women.

The study analyzed health data from more than 180,000 postmenopausal women. After an average follow-up of seven years, physicians diagnosed 5,461 cases of invasive breast cancer.

The research showed that women who had one to two small drinks per day had a 32 per cent greater chance of developing an estrogen-sensitive tumour. Three or more drinks per day boosted the risk by 51 per cent.

About 70 per cent of women who are diagnosed with breast cancer have what are known as estrogen-positive tumours. The growth of these tumours is believed to be fuelled by the presence of both estrogen and progesterone.

For the study's purposes, one glass of alcohol was considered to be three ounces, which means that one drink in some bars and restaurants could actually equal two according to the study's criteria.

The research was conducted by the National Cancer Institute (NCI) and presented Sunday at a meeting of the American Association for Cancer Research (AACR).

Jasmine Lew, of the NCI, said that researchers aren't yet sure how alcohol influences a woman's risk for breast cancer, but it may be that it acts on estrogen levels.

"What we think the alcohol is doing is increasing the amount of estrogen that a woman is exposed to, hence increasing her risk of getting this more common type of breast cancer," said Lew.

Dr. Michael Leitzman, also of the NCI, said that the risk was deemed the same no matter what type of alcohol a woman drank: wine, beer or spirits.

"That points to alcohol itself being the culprit that is associated with increased risk," said Leitzman.

Leitzman added that it's too early to make public health recommendations, but women should take note of the findings.

"One important message to take away from this is that our study found regular alcohol consumption was associated with an increased risk of breast cancer; that included even small amounts of alcohol," Leitzman said.

In England, authorities are planning an advertising campaign to advise women not to drink more than 14 units (or glasses) of alcohol per week.

"If you choose to drink at all, limit your intake to less than one drink a day or don't drink at all," said the Canadian Cancer Society's Heather Logan.

Lew also cautioned that while this research supports earlier studies that link alcohol to breast cancer, more research needs to be done on how alcohol might affect the different types of breast cancer.

From a report by CTV's medical correspondent Avis Favaro and producer Elizabeth St. Philip.

Abstract:

Introduction: Epidemiologic studies have consistently shown an association between alcohol use and invasive postmenopausal breast cancer. Experimental data suggest that alcohol intake increases risk of breast cancer through its effect on estrogen, but observational studies of the association between alcohol use and breast cancer according to hormone receptor status have been sparse and inconsistent. In this context, we investigated if the relation between alcohol and breast cancer differed by hormone receptor status in postmenopausal women.

Methods: We analyzed 184,418 postmenopausal women (mean baseline age of 62 years) in the prospective NIH-AARP Diet and Health Study. At baseline, we assessed alcohol and other nutrient intakes with a food frequency questionnaire, and collected data on demographics, lifestyle, and medical history. We used Cox proportional hazards models to calculate relative risks (RR) and 95% confidence intervals (CI), adjusting for age, race, height, body mass index (BMI), physical activity, smoking history, parity, age at first birth, age at menopause, family history of breast cancer, frequency of breast biopsy, hormone replacement therapy (HRT) use, and intakes of fat, folate and energy.

Results: During an average of 7 years of follow-up, we identified 5,461 invasive breast cancer cases. 2,391 cases had hormone receptor status information: 1,641 ER+/PR+ cases, 366 ER-/PR-, 336 ER+/PR-, and 48 ER-/PR+ cases. 30.0% of women did not drink alcohol; the mean alcohol intake among drinkers was 8.2g/day (10th-90th percentile = 0.4-20.1 g/day). Alcohol was associated with increased risk of breast cancer: compared to no alcohol, the multivariate RR(95% CI) for <5, 5-<10, 10-<20, 20-<35, 35-<45 and >45g/day of intake, were 1.04 (0.98-1.11), 1.05 (0.93-1.17), 1.14 (1.03-1.26), 1.25 (1.09-1.42), 1.32 (1.00-1.74), 1.38 (1.17-1.62) ( p for trend<0.001), respectively. ER+/PR+ tumour types showed a stronger association with alcohol than ER-/PR- tumour types: compared to no alcohol, the multivariate RR(95% CI) for <1, 1-<3, and ��3 drinks/day, were, respectively, 1.07 (0.95-1.20), 1.32 (1.12-1.56), 1.51 (1.13-2.02) for ER+/PR+ tumours, 1.02 (0.80-1.30), 1.48 (1.05-2.08), 0.76 (0.35-1.66) for ER-/PR- tumours, and 1.11(0.86-1.44), 1.17 (0.80-1.71), 1.56 (0.85-2.89) for ER+/PR- tumours. The associations were similar for alcoholic beverage types. Compared to no intake, the multivariate RR (95% CI) for 1-<3 and ��3 drinks/day were 1.20 (0.99-1.55) and 1.73 (1.22-2.46) for beer; 1.20 (1.07-1.35) and 1.41 (0.87-2.28) for wine; and 1.27 (1.12-1.44) and 1.25 (1.04-1.51), respectively, for liquor. No significant alcohol-breast cancer interactions were observed with BMI, HRT use, family history of breast cancer, and folate intake.

Conclusion: Alcohol consumption, even at moderate levels, increased the risk of breast cancer. This positive association was largely confined to ER+/PR+ tumours