Dear BBC, That Was Confusing

2 11 2011

Damned if you do, damned if you don’t…

Today I learned that “regularly drinking even a small quantity of alcohol could increase the risk of breast cancer.” But, moderate intake of alcohol can protect against heart disease… so, to drink, or not to drink? And if you decide to keep drinking, are you really hurting your chances?

According to the story, drinking from 3 to 6 glasses of wine a week  was linked to a 15% increase in risk of developing breast cancer.

In women who never consumed alcohol, there were 281 breast cancers per 100,000 women per year.

That increased to 333 cancers for people drinking between three and six glasses of wine per week. There was a much greater increase, to 413, for those consuming more than 19 glasses.

I suck at numbers, but I’ll do my best. I also have Mayo Clinic’s “Cancer Risk: What the Numbers Mean” article to help me along the way, as well as‘s article on absolute and relative risk.

First, I want to point out that 281 out of 100 000 is a very small number, about 0.28%

I will assume they are talking about relative risk, and not absolute risk. When one talks about absolute risk one talks about the “actual numeric chance or probability of developing cancer during a specified time period”. Relative risk, on the other hand, is a comparison value. Relative risk  “shows the strength of the relationship between a risk factor and a particular type of cancer by comparing the number of cancers in a group of people who have a particular exposure trait with the number of cancers in a group of people who don’t have that trait.

If the study is talking about  relative risk, then we can assume that a person that drinks 3 to 6 glasses of wine a week has a 15% greater chance of developing breast cancer in relation to non-drinkers.

Mayo Clinic says it much better:

A relative risk of 100 percent means your risk is twice as high as that of someone without that risk factor. A 200 percent relative risk means that you are three times as likely to develop that condition.

Risk seems greater when put in terms of relative risk. A 100 percent increase in risk may seem enormous, but if the risk began as 1 in 100 people, the risk is increased to 2 in 100.

To put it in perspective, like Mayo Clinic says, a smoker is 23 times more likely to develop lung cancer than a non-smoker, all things being equal. In percentage, a smoker is 2300% more likely to develop cancer. Then, all things being equal, a drinker has a 15% increased risk of developing breast cancer compared to a non-drinker, that is (drum roll, please) 0.15 times more likely to develop breast cancer.


P.S. This is why epidemiologists, journalists and risk experts say one should put the risk in perspective, distinguish between relative and absolute risk, use comparisons, etc. Really, BBC, Lundgren and McMakin said you wrote the guidelines. Use them!!!




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