Drinking as little as one small glass of wine or beer a day (about 10 g of alcohol) can increase the risk for breast cancer by 5% in premenopausal women and by 9% in postmenopausal women.
This latest warning comes from a new report issued by the American Institute for Cancer Research (AICR) and the World Cancer Research Fund (WCRF). It reviewed 119 studies from around the world, with a total cohort of more than 12 million women and over 260,000 cases of breast cancer.
Commenting on the new finding, Susan K. Boolbol, MD, chief of the Division of Breast Surgery at Mount Sinai Beth Israel Hospital, New York, said, "We have known about the link between alcohol and breast cancer as several studies have shown the association. The issue with those studies is that we did not have an exact amount of alcohol that was known to increase your risk."
"This report clearly states that 1 drink per day will increase your risk. That is major news," Dr Boolbol said in a statement.
On the flip side, the report also found that vigorous exercise (such as running or fast cycling) reduced the risk for breast cancer in both pre- and postmenopausal women, and strong evidence confirmed earlier findings that moderate exercise (such as walking and gardening) also decreases the risk in postmenopausal women.
In premenopausal women, a statistically significant 17% decreased risk was observed (relative risk [RR], 0.83) when women with the highest levels of activity were compared with those who were least active.
The same protective effect was see in postmenopausal women, although to a slightly lesser degree; the most active women had a 10% (RR, 0.90) reduced risk, which was still statistically significant.
Additionally, overall physical activity was also associated with a 13% decreased breast cancer risk (RR, 0.87) in postmenopausal women.
"It can be confusing with single studies when the findings get swept back and forth," said a lead author of the report, Anne McTiernan, MD, PhD, a cancer prevention expert at the Fred Hutchinson Cancer Research Center and a research professor at the University of Washington Schools of Public Health and Medicine, both in Seattle.
"With this comprehensive and up-to-date report the evidence is clear," said Dr McTiernan in a statement. "Having a physically active lifestyle, maintaining a healthy weight throughout life and limiting alcohol — these are all steps women can take to lower their risk."
As previously reported by Medscape Medical News, several studies have highlighted the relationship between exercise and cancer risk, as well as the association between alcohol consumption and cancer risk.
Strong and Weak Evidence
In addition to physical activity and alcohol consumption, the researchers also found other associations with breast cancer risk.
There was a new twist to the findings on obesity increasing the risk for breast cancer. Being overweight or obese throughout adulthood increases the risk for postmenopausal breast cancer, as does a greater weight gain in adulthood, the report confirmed.
However, there was strong evidence that being overweight or obese between the ages of about 18 and 30 years had a protective effect, in that it decreased the risk for both premenopausal and postmenopausal breast cancer.
"It was interesting that this report showed that greater body fatness before menopause protected against premenopausal breast cancer," Dr Boolbol commented. But she emphasized that "once again, this report confirmed the fact that post menopausal weight gain or high body mass index is a risk factor for the development of breast cancer."
Breastfeeding decreased the risk for breast cancer, but developmental factors leading to greater linear growth (marked by adult attained height) increased the risk.
When it comes to diet, however, the evidence was more limited. For specific dietary factors, the report found that consumption of nonstarchy vegetables, for example, might reduce the risk for estrogen receptor–negative breast cancer. The evidence also suggested an association between foods containing carotenoid (which includes carrots, apricots, spinach, and kale) and a reduced breast cancer risk, and limited evidence indicated that diets high in calcium might also lower the risk.
Suggestions for Risk Reduction
For cancer prevention in general, the authors recommend maintaining a healthy weight, keeping physically active for at least 30 minutes every day, and avoiding high-calorie foods and sugary drinks.
In addition, they recommend eating a wide variety of whole grains, vegetables, fruit, and pulses such as beans, along with limiting red meat and avoiding processed meat.
It is best to avoid alcohol, they note, but if alcohol is consumed, the amount should be limited.
"Wherever you are with physical activity, try to nudge it up a bit, either a little longer or a little harder," said Alice Bender, MS, RDN, head of AICR's Nutrition Program, in a statement. "Make simple food shifts to boost protection — substitute veggies like carrots, bell peppers or green salad for chips and crackers and if you drink alcohol, stick to a single drink or less."
Breast cancer is the most common cancer in US women, with over 252,000 new cases expected this year. AICR estimates that one in three breast cancer cases in the United States could be prevented if women d