Obesity Is Linked to 13 Types of Cancer—But It’s Way More Complicated Than That

Your weight isn't the only factor to consider.

Photo: Getty.

This week, the Centers for Disease Control and Prevention (CDC) released a report with some startling statistics. Researchers discovered that while overall rates of cancer have decreased since the 1990’s, the number of overweight- and obesity-related cancers now account for an estimated 40 percent of all cancer cases.

According to their research the rates of non-obesity related cancers decreased by 13 percent, while cancers that are linked to obesity (other than colorectal cancer) increased by 7 percent over a nine-year period (2005 and 2014).

Just looking at the data for 2014, the most recent year available, approximately 630,000 people in the U.S. were diagnosed with one of 13 cancers associated with being overweight or obese. The majority of those patients (two out of three) was diagnosed between the ages of 50 and 74. Plus, 55 percent of all cancers diagnosed in women were linked with having a body mass index (BMI) of at least 25.

The 13 cancers found to be connected with obesity include those affecting the brain membranes, esophagus, thyroid, gallbladder, stomach, liver, pancreas, kidneys, colon, and rectum. They also include cancers found in women, such as ovarian, endometrial, and breast cancers.

But it's not totally clear how obesity affects your cancer risk.

Jack F. Jacoub, M.D., medical oncologist and medical director of MemorialCare Cancer Institute at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, tells SELF he is “absolutely not surprised” by these findings. However, it's important to note that the CDC study cannot prove that having excess weight directly causes any of these cancers. Instead, it may be that people who are overweight are also more likely to develop these cancers for reasons unrelated to weight.

But emerging research suggests that excess weight may contribute to your risk for cancer in subtle, indirect ways. “Obesity creates a degree of inflammation in the body,” he explains. “Inflammation, over time, can lead to tissue damage and subsequent change that perhaps could lead to additional events that could lead to cancer.” He further explains that obesity can produce additional hormones in the body, “and those hormones, at times, may be counterproductive to the person and may contribute to hormone-driven types of cancers.” For instance, having excess weight can increase the body's production of estrogen, which may increase the risk for breast cancer among postmenopausal women.

“Recently, there have been several reports showing [an increase] in younger people getting colon cancer," Anton J. Bilchik, M.D, professor of surgery and chief of gastrointestinal research at John Wayne Cancer Institute at Providence Saint John’s Health Center in Santa Monica, CA, tells SELF. While there are several possible theories, he says the most likely explanation is a combination of obesity, poor nutrition, and lack of exercise.

Your genes, environment, and lifestyle all play huge roles in your cancer risk.

Cancer is a complex group of diseases with many possible causes. “It should definitely be emphasized that weight is not the only risk factor,” states Dr. Jacoub. “Cancer is an interplay between the environment and one’s genetic makeup.”

“We need to be somewhat cautious,” continues Dr. Bilchik. “There is a higher incidence of cancer in people who are obese, but it certainly does not mean every obese patient is going to have cancer. Obesity is really just one factor.”

And considering that 70 percent of all adults in the U.S. are overweight or obese, it may not exactly be the most helpful one to think about. That's one reason why some public health experts suggest focusing on healthy behaviors—exercise, nutrition, sleep—rather than weight itself as a marker of health.

Some of the many other common risk factors for cancer include having a family history of the disease, lack of exercise, alcohol intake, smoking (“Just about every cancer is linked to smoking,” Dr. Bilchik says), and exposures to different types of radiation and chemicals (such as lead, asbestos, radon, x-rays, and ultraviolet rays from the sun).

Your risk for cancer really comes down to a combination of the chronic exposure to these environmental and lifestyle factors on top of your genetic predisposition, Dr. Jacoub says. “You can’t control your genes—they will be that way from day one until your last day. So control what you can control.”

This story originally appeared on Self.

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