risk going up

Example of breast cancer risk going up

Many studies have shown that women who have two or more alcoholic drinks each day have a higher risk of developing breast cancer. (A drink is defined as 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of 80-proof liquor.) You may hear this relative risk described as a percentage or a number:

Compared to women who do not drink, women who have two or more drinks per day have a 25% higher risk of breast cancer. Put another way, they are 25% more likely to develop breast cancer over the course of a lifetime than nondrinkers are. This doesn’t mean that their lifetime risk of getting breast cancer is 25% — it means that their risk of getting breast cancer is 25% higher relative to people who don’t drink. This percentage is how you are likely to see relative risk reported by television, the Internet, and newspapers.

Compared to women who do not drink, women who have two or more drinks per day have a relative risk of 1.25. This number is how researchers and scientific papers would usually talk about relative risk. The number “1” is assigned to the baseline group (women who do not drink), since their risk remains the same. The .25 describes the relative increase in risk for the other group; it is another way of expressing the 25% higher lifetime risk (25% = .25).


Another way of saying this is that women who drink two or more alcoholic drinks per day have 1.25 (1 + .25 = 1.25) times the risk of developing breast cancer than women who do not drink.


Relative risk can be a tricky concept, because most people tend to focus on the reported percentage — e.g., 25% higher risk — which sounds alarming. Yes, a 25% higher risk of developing breast cancer (relative to people who don’t drink) is significant, but it doesn’t tell a woman what her lifetime risk is if she drinks two or more alcoholic drinks per day for the rest of her life. Since women in this group have 1.25 times the risk of developing breast cancer, it’s necessary to multiply the absolute risk of breast cancer for women in the general population (13%, or .13) by relative risk (1.25):

.13 x 1.25 = .1625, or 16.25%. This means that a woman’s absolute lifetime risk of developing breast cancer if she drinks two or more alcoholic drinks per day is just over 16%, or roughly 1 in 6, versus 13%, or 1 in 8, for women who do not drink.

Many different factors can increase and/or decrease your risk of developing breast cancer. Online tools such as the National Cancer Institute’s Breast Cancer Risk Assessment Tool allow you to input individual information to calculate your risk.



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