New research suggests that as little as one glass of wine each day may increase breast cancer risk by 5 percent.
Worldwide, breast cancer is the second leading cause of cancer-related death among women. In the United States, almost 231,000 women were diagnosed with breast cancer in 2013, along with more than 2,100 men.
There are several risk factors that increase a woman's likelihood of developing breast cancer. These include older age, early menarche, and having a family history of breast cancer.
While there is little a woman can do to control these risk factors, there are additional lifestyle risk factors that women can adjust in order to lower their risk.
A new report conducted by the American Institute for Cancer Research (AICR), in collaboration with the World Cancer Research Fund, examined several risk factors for breast cancer, including alcohol, diet, and weight.
Alcohol increases breast cancer risk, exercise lowers it
The report consisted of a meta-analysis of 119 existing studies that together examined the clinical data available on 12 million women, adding up to a total of 260,000 cases of breast cancer.
According to the report, as little as 10 grams of alcohol per day - the equivalent of a small glass of wine or beer - raises the risk of premenopausual breast cancer by 5 percent. The same amount of alcohol raises the risk of postmenopausal breast cancer - the most common form of breast cancer - by 9 percent.
Ten grams of alcohol amounts to less than the "standard" drink, which currently consists of 14 grams of alcohol.
Furthermore, the report confirmed that being overweight, having obesity, or just gaining more weight in adulthood increases the likelihood of postmenopausal breast cancer. Conversely, moderate exercise decreased the risk of both pre- and postmenopausal cancer.
Postmenopausal women who were the most active were 10 percent less likely to develop breast cancer compared with their least active counterparts. For premenopausal women, this drop in risk was 17 percent.
Foods high in carotenoids may decrease breast cancer risk
In terms of diet, the report found "limited evidence" that non-starchy vegetables may decrease the risk of the so-called estrogen-receptor-negative breast cancers. These represent a rarer type of breast cancer, but one that may be more aggressive and have a poorer prognosis.
Non-starchy vegetables include broccoli, cabbage, brussel sprouts, leeks, beans, and spinach. The University of Michigan in Ann Arbor offers a full list of non-starchy vegetables.
The report also found a link between diets high in dairy, calcium, and carotenoids, and a lower risk of breast cancer. Carotenoids are pigments synthesized by plants, which often account for their yellow, orange, or red color. Foods with high carotenoid levels include pumpkins, apricots, carrots, spinach, and kale.
The evidence for the link between carotenoids and a lower risk of breast cancer is, however, also limited, and the authors admit that more research is needed to confirm the results.
Dr. Anne McTiernan, Ph.D. - one of the lead authors of the report and cancer prevention expert at the Fred Hutchinson Cancer Research Center - comments on the findings:
"The findings indicate that women may get some benefit from including more non-starchy vegetables with high variety, including foods that contain carotenoids. That can also help avoid the common 1 to 2 pounds women are gaining every year, which is key for lowering cancer risk.
With this comprehensive and up-to-date report the evidence is clear: 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."
Alice Bender, AICR's head of nutrition programs, also comments on the results, recommending a few more measures that women can take to lower their risk:
"Wherever you are with physical activity, try to nudge it up a bit, either a little longer or a little harder. 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," Bender says.
"There are no guarantees when it comes to cancer, but it's empowering to know you can do something to lower your risk," she adds.