Alcohol consumption is associated with increased risk of breast cancer. There is about 30-50% increase in breast cancer risk from 15-30 grams/day (about 1-2 drinks/day) of alcohol consumption. Overall, for each additional 10 grams of alcohol consumed per day, the relative risk of breast cancer is increased by 7%. The exact mechanism how alcohol increases the risk of developing breast cancer is not fully clear. However, some of the mechanisms may be-
Alcohol (ethanol) is broken down into acetaldehyde which can cause changes in our DNA, interfere with the anti-oxidative defense system and DNA synthesis and repair which leads to the development of the cancer cells. Also the cells damaged by alcohol try to repair themselves which can lead to alteration in DNA causing cancerous changes. It can also decrease the ability of the body to breakdown and excrete certain harmful chemicals. It also inhibits the absorption of certain useful nutrients like folate(vitamin) which is more common in heavy drinkers. These low levels of folate can lead to breast cancer. Heavy drinking can also leads to obesity which again is a risk factor for breast cancer.
Alcohol can also raise estrogen levels in the body which may lead to changes in breast density, induce hormone-receptor mediated cell proliferation and genetic alterations. It can also increase the risk of breast cancer recurrence in the survivors. Even during cancer treatment one must avoid alcohol as it can increase the side effects of certain drugs used in cancer treatment. Thus it is recommended that women should not consume >1 drink/day and >7 drinks/week . The recommendation for alcohol intake is less for women as compared to men because of they have a comparatively small body size and their bodies tend to breakdown alcohol more slowly. The amount of alcohol consumed and not the type of alcoholic beverage seems to be the most important factor in raising cancer risk.