Obesity linked to increased cancer risk

Two out of three adult Americans are at greater risk for getting cancer — and for dying of it — than they need to be, according to a story in the Chicago Tribune. Not because of smog in their air or radon in their basements. Not because of tobacco in their cigarettes or mutations in their genes.

No, the particular cancer risk shared by these 150 million or so Americans comes from having too many calories in their diet and too little exercise in their daily lives.

In other words, from being overweight.

It’s widely known that simply being overweight, let alone obese, dramatically increases the risk for high blood pressure, heart attacks, strokes and diabetes. But according to a 2009 survey by the American Institute for Cancer Research, only about 50 percent of Americans know that size also matters when it comes to cancer.

The risk is not trivial. The same institute estimates that every year about 100,000 Americans get a cancer they wouldn’t have gotten if they had kept their weight in check. And researchers have estimated that about 14 percent of cancer deaths in men and 20 percent in women could be avoided by this same restraint.

Obesity can raise the risk for a number of major cancers — colon, postmenopausal breast, endometrial, kidney and esophageal — the National Cancer Institute says, and when paired with physical inactivity, it can be held liable for 25 percent to 30 percent of cases of those cancers. Obesity has also been linked to a number of other cancers, including liver, gallbladder, pancreatic and ovarian.

“Obesity is almost like the new smoking,” says Dr. Anne McTiernan, director of the Prevention Center at the Fred Hutchinson Cancer Research Center in Seattle. “The effect isn’t as big for most cancers, but it’s so prevalent that it will have a huge impact.”

Indeed, the National Cancer Institute estimates that smoking accounts for 37.5 percent cancer deaths in men and 22.8 percent in women. But smoking does most of its dirty work in lung cancer victims. When lung cancer is taken out of the picture, smoking can only be blamed for 12 percent of cancer deaths in men and 6 percent in women — fewer than can be chalked up to excess pounds.

No one knows for sure exactly how weight increases cancer risk, but it’s likely that it does so in multiple ways, with the precise mechanism differing from cancer to cancer. High levels of estrogen, insulin and inflammatory compounds are among the suspects that have been implicated in research to date.

A more precise understanding of the biology behind all this may someday lead to drugs that can mitigate the damage. In the meantime, of course, there’s an excellent way to avoid the obesity risk, and that’s to never become obese at all.

“That would require major lifestyle changes for many of us, and making such changes is exceedingly hard,” said Dr. John Glaspy, an oncologist at UCLA’s Jonsson Comprehensive Cancer Center.

“Sure, we could make it a death penalty offense to sell sugared drinks. But short of such extreme modes of encouragement, a widespread thinning of America is not to be expected anytime soon.”

Not only is there strong evidence that if you’re overweight, you’re more likely to die of cancer. It’s also been shown that the more overweight you are, the more deadly the trend gets, according to a landmark study published in the New England Journal of Medicine in 2003.

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