Over recent years, many studies demonstrated a definite link in the incidence of certain cancers and the presence of obesity. These cancers include but are not limited to cancers of the esophagus, pancreas, breast, colon and rectum, endometrium, kidney, thyroid and gallbladder. There was one study that estimated 34,000 new cancer cases in men and 50,500 in women were due to obesity. If this trend continues, it has been projected that there will be 500,000 new cancer cases in the US due to obesity.
There are several mechanisms that have been suggested to explain why this is happening. For one thing, fat cells produce estrogen, and high levels have been shown to cause breast, uterine and other cancers. People who are obese also tend to have elevated levels insulin and insulin- like growth factor -1 (IGF-1) in their blood. These have also been shown to increase the incidence of certain tumors. Additionally, fat cells produce adipokines, hormones that stimulate or inhibit cell growth. Tumor growth regulators, including mammalian target of rapamycin (mTOR) and AMP- activated protein kinase, are directly and indirectly affected by fat cells. Patients with obesity also have chronic low-level inflammation that increases cancer risk as well. Other possible factors include altered immune responses, effects of nuclear factor kappa beta system and oxidative stress. Abdominal obesity and weight gain in adulthood were also shown to play a causative role in certain cancers. In the Nurses’ Health Study, it was found that overweight women who never used HRT cut their post-menopausal cancer risk in half when they lost weight and kept if off.
Not only does obesity impact the development of cancer, it also affects its prognosis. In a high profile study done by a group at the American Cancer Society, mortality risk was shown to be increased in obese patients. This was shown to be true in men who had prostate, kidney, colorectal, esophageal, stomach, pancreatic and liver cancers. In women, this was demonstrated in those diagnosed with colorectal, ovarian, breast, cervical, kidney and uterine cancers. This was also seen to be true for cancers where there has not been shown to be a clear link between obesity and specific cancer types. Also, obese men who were diagnosed with prostate cancer tended to have more aggressive disease and to present at more advanced stages.
The most recent report in 2014 from the American Association for Cancer Research (AACR) stated that being overweight or obesity was responsible for nearly 25% of relative cancer risk. This ranked second only to tobacco use. More concerning is that when you combine obesity with lack of exercise and poor diet, the relative contribution rises to nearly 33% of newly diagnosed cancers in the US. In November 2014, the American Society of Clinical Oncology (ASCO) issued a position statement that obesity is rapidly overtaking tobacco use as the number one preventable cause of cancer.
While studies have clearly demonstrated that obesity causes certain cancers, the exact mechanism is unclear. While more studies are needed to discover these pathways, the true solution lies in maintaining a healthy weight through diet and exercise.
Copyright secured by Digiprove © 2019 Linda Girgis, MD, FAAFP
Sadly,
This is our new reality—and has nothing to do with shaming, blaming, or profiling: the science is there to prove it: excess weight matter.
The onus rests on patients, physicians, patient’s family, public, health care, law makers, educators, business leaders, politicians to address, not per se, obesity, but making healthier lifestyles a reality and part of every family and individuals’s life.
This includes addressing minimum wage, poverty, and promotion of ACTIVE commuting and not only teaching it in schools but implementing it.
Incentivize—it works.
Or perhaps with advances in cardiac and diabetic management, we are keeping those with obesity alive long enough to get these cancers. It would be interesting to look back to 1960’s pr 1970’s statistics and see if the correlation with obesity were present then. That would affirm a physiologic link. If there were no correlation then but there is now, this new correlation may be a disease of medical progress as we manage obesity related co-morbidity more effectively.