The association between obesity and cancer is less well understood and appreciated by both doctors and the general public than the better known links between obesity and cardiovascular disease and diabetes.
According to a review of cancer developments regarding obesity and cancer in an oncology newsletter, there are several theories about the mechanisms of action that cause excess fat tissue to increase cancer risks.
The bottom line is clear, however: obesity directly affects cancer development, detection, diagnosis, severity of disease, treatment, and mortality. As such, the linkage between obesity and cancer pervades the entire continuum of cancer development and progression.
Yet more than nine out of ten Americans remain unaware of the linkage between obesity and cancer, what some are now calling “the new smoking” due to its role in promoting a broad range of cancers. The American Cancer Society predicts obesity will soon overtake smoking as the primary preventable cause of cancer.
Yet we have few of the public awareness campaigns that finally began to reverse the rate of smoking in America, which means the “war on cancer” is likely to prove as futile as the war in Afghanistan – unless and until we get the word out to more overweight Americans that they’ve got a lot more to worry about than looking good for high school reunions, weddings and beach outings.
The following brief video discusses the contrast of our lack of focus on obesity and our success in combating smoking in America:
Obesity and Cancer Specifics
Here are a few specifics:
The U.K.’s Million Women Study tracked over a million women for 7 years and found 12% increased cancer risk for all cancers associated with both overweight and obesity. Researchers thought this likely understates the true association given the lag time for malignancies to develop. On the subject of obesity and cancer, here’s what M.D. Anderson Cancer Center researcher Dr. James Abbruzze has said:
“I think this is a big worry in overall trends of cancer. Between the overall aging of the population and the obesity epidemic, we may be poised to lose some of the gains that we’ve made (toward decreasing cancer mortality). I think it is a huge problem”;
In the U.S., this translated into over 40,000 cancers annually in 2002 – roughly as many as die from breast cancer and a number that’s likely much higher today given the higher obesity rate and lag time for cancers to develop;
Some cancers are more strongly associatedwith obesity than others. Following are some cancers the Million Women Study found to have the strongest indications for increased risk with obesity:
Endometrial cancer – 189% increased risk;
Esophageal cancer – 138% increased risk;
Kidney cancer – 53% increased risk; and
Pancreatic cancer – 24% increased risk.
Screening for cancer is more difficult for obese people – mammograms are harder to read and PSA tests less reliable due to increased blood volume in obese men that dilutes PSA to lower levels, resulting in more “false negatives” (failures to detect cancers);
Obese people are also less likely to seek cancer screening – according to the Johns Hopkins physician whose study found that women with a BMI over 40 were 38% less likely to receive PAP testing for cervical cancer…
“There is literature that shows that obese women delay medical care, and then certainly there is a perceived lack of respect from health care providers” (see Our Healthcare Sucks for more on this);
Cancer treatment is complicated by obesity – many surgeries are made more difficult by obesity and by the co-morbidities (other diseases) that often accompany it;
As a result, the obese are more likely to die from cancer – according to a study on obesity and cancer in The New England Journal of Medicine, men with a BMI over 40 have a 52% higher risk of death from all cancers and women a 62% increased risk compared to non-obese people.
Weight gain also increases women’s risk for breast cancer, at least among postmenopausal women.
A study of the effects of weight gain on breast cancer found women who gained 22 pounds or more post-menopause increased their breast cancer risk by 18%, while women who had gained about 55 pounds since age 18 increased their breast cancer risk by 45% compared with those who maintained their weight.
There’s Good News?
The good news about obesity and cancer is women who lost about 22 pounds post-menopause had a 57% lower risk of breast cancer compared to women who maintained their weight. Post-menopausal women may find this an incentive to lose weight.
Overweight women appear to have a lower risk of breast cancer before menopause, however, possibly due to “reduced hormonal cycling and reduced total hormonal exposure”.
This is one example of the (temporarily) protective effects of excess weight in women. Unfortunately, it turns to disadvantage after menopause, when overweight and obese women experience higher rates and increased severity of breast cancer.
A study of obesity and cancer among overweight women and women with insulin resistance (elevated insulin levels) found they were about…
“50% more likely to be diagnosed with an advanced breast cancer tumor…Women with insulin resistance or who were overweight were less likely to be diagnosed with stage 1 breast cancers but at greater risk of being diagnosed with stage 2 to 4 tumors – larger, more advanced cancer.”
Men don’t escape this association between obesity and cancer. One study found a 40% increased rate of prostate cancer death, not just incidence, in overweight and obese men.
According to one in-depth analysis of obesity and cancer of the prostate:
“Obesity may be associated with more advanced disease; one study reported obese patients with prostate cancer were more likely to be younger and have more advanced disease”.
For those with the interest and patience to learn about the obesity and cancer linkage in greater depth, the following video explores the current medical thinking on the subject (from The Obesity-Cancer Connection Panel at the Metabolism, Diet and Disease conference held in Washington DC from 29-31 May 2012):
Obesity = Severity
None of this is surprising, as obesity appears to contribute to greater disease severity generally. A study of diabetics followed in the Nurses’ Health Study found women’s stroke risk rose with obesity:
Those with a BMI of 27-28.9 had 80% more strokes;
Those with a BMI of 29-31.9 had 90% more strokes;
While those with BMIs over 32 had 140% more strokes, or almost 2½ times those of normal weight women.
This suggests that the more advanced severity and complications seen among obese and overweight patients with various cancers isn’t limited to cancer and occurs across a range of diseases.
So if you’re New Year’s resolution to drop some pounds has started to wane, you might want to renew it now that you know the stakes are far greater than your appearance.
And if you’re comfortable that your current weight poses no greater medical risk, you still face the challenge of avoiding weight gain that usually accompanies the aging process.
What do you think? Do you think the deadly health effects of excess weight and belly fat will ever catch up with our obsession with its cosmetic effects?
Add to the conversation by commenting below.
 Opportunities and Strategies for Breast Cancer Prevention Through Risk Reduction. CA Cancer J Clin 2008.
 Pharmacotherapy of Obesity. Hofbauer, et al. CRC Press. 2004. P.107.
 Diabetes, the Metabolic Syndrome, and ischemic Stroke: Epidemiology and possible mechanisms. Diabetes Care 30:3131-3140, 2007.