Alcohol and Breast Cancer in Women

Journal of the American Medical Association 1998;279-535-540

This study concluded that "Alcohol consumption is associated with a linear increase in breast cancer incidence in women over the range of consumption reported by most women. Among women who consume alcohol regularly, reducing alcohol consumption is a potential means to reduce breast cancer risk."

It's a good thing that last sentence was qualified with "potentially." The association referred to in the first sentence is far from established.

This study is a "meta-analysis"--a pooling of the results from existing studies. Why were the results pooled? Because individual studies fail to convincingly link alcohol consumption with breast cancer.

As the authors of this study stated "Numerous studies have shown modest [translation: nothing meaningful] increases in risk associated with high alcohol consumption; however many of these studies have been relatively small and the associations have not always been statistically significant."

Unfortunately for this study, the more things change, the more they stay the same.

This study classified alcohol consumption by grams per day into seven categories: 0; >0 to <1.5; 1.5 to < 5.0;5.0 to < 15.0; 15.0 to < 30.0; 30.0 to < 60.0; and >=60.0. [in the U.S., a bottle of beer was assumed to have 13.2 g of alcohol; a glass of wine, 10.8g and a shot of liquor, 15.1g.]

But the only statistically significant association between alcohol consumtion and breast cancer in the meta-analysis was reported in the 30.0 to < 60.0 consumption category. And when you look at the six studies individually, only 2 of the 6 associations in this category are statistically significant.

Although the authors report there is a statistically significant linear increase in breast cancer with alcohol consumption (roughly 9 percent for every 10g per day of alcohol), this "trend" is based on six individual data points, only one of which is statistically significant (i.e., the reported association in the 30.0 to < 60.0 exposure group).

And I wouldn't want to overlook that all the reported associations are weak (i.e., increases in incidence less than 100 percent) and therefore suspect due to the usual shortcomings of the epidemiologic method--especially that 9 percent figure. A 9 percent increase from an epidemiologic study? Puh-lease!

There are lots of reasons why women shouldn't drink excessively. I'm just not sure yet that preventing breast cancer is one of them. And what's worse is scaring women from alcohol consumption which is associated with a decrease in heart disease-- a far more common women's health issue than breast cancer.

Finally, even if alcohol consumption is associated with breast cancer incidence, that association would be in evidence only on a population basis. This study provides not information on how alcohol consumption affects breast cancer incidence in individuals.

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