11/07/2007

Obesity 'fuels cancer in women': Wrongly Scaring People

"Fuels cancer" sounds pretty bad. Surely the claim that just being "overweight" increases the risk of cancer is pretty scary. Back in graduate school one of the many points that I learned from Ed Leamer was there is an important difference between something that is statistically significant and something that is economically significant. The BBC claims that:

About 6,000 middle-aged or older women in the UK develop cancer each year because they are obese or overweight, a Cancer Research UK-funded study says. . . . .


Ironically, there is another study that just came out that claims simply being "overweight" lowers one's chance of getting cancer:

Being 25 pounds overweight doesn’t appear to raise your risk of dying from cancer or heart disease, says a new government study that seems to vindicate Grandma’s claim that a few extra pounds won’t kill you. . . . .


Well, let's just assume for a minute that the first scary claim is correct and also that the cancer is not the result of something that is also causing the women to be fat (e.g., depression may cause both obesity and cancer). According to the BBC article 4.5 million women are between 50 and 64 in the UK and 57 percent of those are obese or overweight. That comes to 2,565,000. Of those women, if we believe these claims, 6,000 will get cancer or any type each year (it would have been nice to know how many of them died from it, but that is another issue). Anyway, that means that 0.23 percent of these overweight or obese women get cancer each year because of their weight. I wouldn't want to be that less than quarter of one percent, but this doesn't sound like something to panic over. While there is no breakdown for the cancers "caused" by overweight, about one-third of cancers generally are said to result in death so that if true for these cancers, it means that .078 percent die. That is less than one tenth of one percent die from cancer.

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