Obesity May Cause Nearly Half a Million Cancer Cases Each Year


The obesity epidemic may be responsible for a spike in cancer cases — especially in women. (Time Roberts/Getty Images

You know that excess weight is hard on your heart, and that obesity and Type 2 diabetes go hand in hand. Now, a new study in The Lancet Oncology adds cancer to the growing list of problems we can blame on our ballooning waistlines.

For the study, researchers gathered body mass index (BMI) data from 2002 for thousands of people in 184 countries. They then examined cancer rates in 2012, focusing on those previously linked to obesity (called high-BMI-related cancers), such as colon, kidney, pancreatic, and postmenopausal breast cancers. Since obesity isn’t thought to directly cause the Big C — only to promote it — the scientists assumed that there’d be a 10-year lag time between being diagnosed with obesity and developing cancer.

Their frightening finding: 3.6 percent of new cancer cases in 2012 (excluding non-melanoma skin cancers) could be attributed to obesity. That translates to about half a million new diagnoses worldwide — and that’s in just a one-year period.

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Excess body weight was to blame for an even higher rate of cancers in women across the globe — 5.4 percent — compared with 1.9 percent in men.

In North America, the region with the highest rate of obesity-attributable cancers (111,000 new cases in 2012), the numbers were even more alarming: Nearly one in 10 new cancer cases in women could be linked to a high BMI. About two-thirds of the cases in women were postmenopausal breast cancer and a certain type of uterine cancer, both of which have specifically been tied to excess body weight, says study author Melina Arnold, a researcher at the International Agency for Research on Cancer in France.

So what’s the fat-cancer connection? The underlying mechanisms differ significantly by cancer type, says Arnold. However, hormones are consistently identified as the culprit linking body weight to tumor development. “Using animal models, we believe it’s mostly related to hormone changes [with obesity],” says George Wang, a professor of human nutrition at Kansas State University who has studied obesity and cancer risk (he was not involved in the new study). “For example, for breast cancer, one of the pathways is related to hormones that are produced by fat tissue and can lead to cancer development,” Arnold says.

Wang’s lab has zeroed in on a hormone that stimulates cell growth, called insulin-like growth factor 1, or IGF-1. “It’s what we call a survival hormone,” he tells Yahoo Health. In healthy people, it prevents apoptosis, or programmed cell death. The problem is, obese people’s levels of IGF-1 may be twice that of a normal-weight person, allowing cells to proliferate too quickly. “We believe that increases cancer risk,” says Wang.

If average BMI hadn’t increased since 1982, the researchers calculated, 118,000 new cases of high-BMI-related cancers could have been avoided in 2012. Specifically, nearly 11 percent of all esophageal adenocarcinoma cases (a type of cancer in the esophagus), 8.5 percent of all corpus uterine cancers (the kind that occurs in the body of the uterus), and 5 percent of all kidney cancers might have been prevented if the global rise in BMI hadn’t continued since the early 1980s.

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“Other important risk factors for cancer, such as smoking, are declining, but we see the proportion of overweight and obese men and women still rising in most countries,” study co-author Nirmala Pandeya said in a statement. “If this trend continues we are likely to see an increasing number of people diagnosed with cancers that could have been avoided by maintaining a healthy weight.”

That’s what makes stopping obesity before it starts so critical. And, according to Arnold, that needs to take place on both an individual level (e.g., limiting calorie intake, exercising) and a societal level (e.g., making healthy foods available, affordable, and accessible).  “We need to increase awareness and allow for more supportive environments and communities, which are fundamental in shaping people’s choice,” she says. “Prevention is key, especially because we expect the burden of cancer associated with obesity to increase in the future.”

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