Many studies support a link between alcohol intake and an increased risk of breast cancer. One analysis pooling the data from 53 studies found that for every one alcoholic drink consumed per day, the relative risk of breast cancer increased by about seven percent (a 1.07-fold increase in risk). Overall, women who drink two to three alcoholic beverages per day have a 20 percent greater risk of breast cancer (a 1.2-fold increase in risk) than non-drinkers.
Alcohol may increase the risk of breast cancer in a number of ways. It can alter the way a woman's body metabolizes estrogen, causing blood estrogen levels to rise, which may in turn increase the risk of breast cancer. Drinking alcohol can also reduce blood levels of the vitamin folic acid. Folic acid plays a role in DNA synthesis and repair. Low levels of the vitamin may make it more likely that DNA is incorrectly copied when cells normally divide. Such errors can lead cells down a pathway to become cancerous.