Seitz said the team's research controlled for various other factors that might affect risk, such as obesity.
Two American experts put the new report into perspective.
The association between moderate alcohol use and a slightly increased risk of developing breast cancer has been reported before, said Dr. Joanne Mortimer, director of Women's Cancer Programs at the City of Hope Comprehensive Cancer Center in Duarte, Calif.
"This is an update of the evidence linking alcohol to breast cancer," said Susan Gapstur, vice president of the epidemiology research program at the American Cancer Society.
By including both newer studies and older ones, Gapstur said, "we are basically getting to the point where we can more precisely estimate the risk of light alcohol consumption."
As the link between alcohol and breast cancer strengthens, women may wonder how to strike a balance between breast health and heart health, since moderate alcohol has been found to be heart-healthy.
Follow the American Cancer Society guidelines, Gapstur said.
"Our guidelines say, for overall health, if you don't drink, don't start," she said. "If you do, it's best to limit your consumption to one drink a day if you are a woman."
If you are at high risk of breast cancer, limiting consumption to even less may be wise, she said.
Mortimer, however, said many women are at increased risk of breast cancer because of genetic factors.
"Lifestyle changes won't impact much," she said.
Seitz has another opinion. "The heart benefits hold true only for a subgroup of individuals," he said. "Those who have more than one risk factor for coronary heart disease and especially the elderly may benefit from small amounts of alcohol. Younger people do not."
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