It found strong evidence that drinking the equivalent of a small glass of wine or beer a day (about 10 grammes alcohol content) increases pre-menopausal breast cancer risk by five percent and post-menopausal breast cancer risk by nine percent.
"I was most surprised by the alcohol result, that risk increases at just one drink a day, on average", McTiernan said, adding that "the increase with one drink a day was small ... but the risk goes up from there".
"We're not saying no one should ever drink at all, we're just saying if you do drink, even trying to keep it down to less than one drink a day would be a smart choice", Bender says.
That doesn't mean that the occasional glass of wine or beer will cause cancer, and light drinking can lower the risk of heart disease. "On WCRF's figures, that would lead to 1 more of them developing a breast cancer during their lifetime". For every 5-point increase in body mass index (BMI), the risk of breast cancer rose by 12 percent, McTiernan said.
To get a better understanding of the relationship between alcohol and breast cancer risk, McTiernan and colleagues performed a meta-analysis - they evaluated data from 10 previous studies involving pre-menopausal women and 22 studies involving post-menopausal women.
Breast cancer is the leading type of cancer in American women.
Research on alcohol consumption and health risks is always going to have limitations, says Boolbol, since most studies in this area-including the studies in both of these reviews-are observational, rather than randomized clinical trials.
"Mice exposed to human triple-negative breast cancer cells experienced significantly reduced metastastic growth in their lungs after being treated with luteolin", said researcher Salman Hyder.
Cancer experts say the findings don't tell us anything new about the link between alcohol and breast cancer, which is already well known.
One of the largest cancer prevention studies of its kind to date reached a sobering conclusion. They are not saying that every slice of bacon you eat or glass of rosé you drink jacks up your chances of getting the disease.
Breast cancer is the No. 2 cancer killer of USA women, after lung cancer.
To the extent that being overweight has been found to increase an older woman's breast cancer risk, McTiernan said eating a diet full of fruits and vegetables can help women keep their weight down.
"It may be the most common cancer in women worldwide, but our evidence shows that there are steps that women can take to significantly reduce their breast cancer risk". A daily alcoholic drink also heightened the risk of post-menopausal breast cancer by 9%. Meanwhile, unhealthy weight increases the risk for many cancers, because certain types of body fats release unsafe hormones and compounds. Researchers are still trying to pinpoint how alcohol influences breast cancer risk, and some research suggests it increases the hormone estrogen. "There is no evidence that we can balance risks that way; it's not something we have control over".
And being overweight or obese throughout adulthood may increase the risk of postmenopausal breast cancer, the researchers found in the new report. However, more research is needed. The report may be slightly skewed because of self-reporting, grant said.
The side effects of drinking alcohol are not unknown. The report also left out genetics, he said. That's an average; your personal risk (because of genetics or environment) may be more or less.
Maintain weight at a normal level.
Exercise at least 150 minutes per week at a moderate intensity or greater.
Ruddy also recommends exercising and minimizing alcohol intake.