Risk factors: Obesity is primarily caused by poor diet (excessive intake of calories) and physical inactivity. Weight gain may be caused in part by the abundance of readily available high-calorie food choices and the lack of physical exertion in modern lives, psychological factors such as stress or depression, physical conditions such as hypothyroidism, and certain medications including migraine medications and antidepressants.
Etiology and the disease process: Many researchers have studied obesity and its relationship to an increased incidence of certain cancers. It is believed that fat cells in the body produce hormones and other substances that affect cell growth. Obese people have significantly increased levels of these compounds because of the increased number of fat cells, which can have potentially important effects on cellular growth and planned cellular death (apoptosis), perhaps allowing damaged cells to survive and grow into tumors. The roles of estrogen, insulin, insulin-like growth factor-1 and insulin-like growth factor-binding protein-3, leptin, and cytokines, as well as other substances and growth factors, are being examined for their relationship to obesity-associated cancers.
An example of these actions by fat tissue can be found in postmenopausal breast cancer, which is known to have a higher incidence rate in obese women. Estrogen, important in the reproductive cycle, is produced by fat tissue in addition to being produced by the ovaries. After menopause, when the ovaries stop producing hormones, fat tissue becomes the most important estrogen source. In obese women, postmenopausal estrogen levels are 50 to 100 percent higher than in women who are not overweight or obese. As a result, estrogen-sensitive tissues in obese women are overexposed to estrogen stimulation, leading to a more rapid growth of estrogen-receptor-sensitive breast tumors. Researchers believe that the fat cells stimulate surges of hormones, insulin, proteins, and the other substances mentioned above that may, in turn, cause reactions that initiate uncontrollable growth among certain cell types. A 2010 systematic review in Breast Cancer Research and Treatment found that obese breast cancer patients had lower survival rates than non-obese patients.
Incidence: According to the American Cancer Society, the risk of cancer from obesity is similar to the risk from using tobacco. Obesity has reached epidemic proportions and affects the entire population, regardless of age, gender, race, or ethnicity. In the United States, obesity has been increasing at an alarming rate. In 1980, about 15 percent of adults were classified as obese; by 2004, that number had more than doubled to about 33 percent, a level maintained over the following decade. According to the US Centers for Disease Control and Prevention (CDC), between 1984–94 and 2009–10, the number of adults classified as severely obese had increased from 2.8 percent to 6.3 percent. A 2013 American Journal of Public Health study found that between 1986 and 2006, overweight and obesity accounted for 5 percent of deaths among African American men, 15.6 percent among white men, 26.8 percent among African American women, and 21.7 percent among white women.
Childhood obesity has been at the forefront of concern because of the staggering numbers of overweight children and the projected long-term health effects. The National Cancer Institute reported in 2012 that between 1988 and 1994, only about 10 percent of American children and youth aged two to nineteen and 56 percent of adults were obese. By 2012, 16.9 percent of children and adolescents were obese, as were 34.9 percent of adults, according to the National Health and Nutrition Examination Survey results published in 2014 in JAMA. Overweight and obesity are most common among black and Hispanic women, with the similar patterns seen for children and adolescents in these groups.
Studies have increasingly linked obesity and cancer. Many studies show that the greater the degree of obesity, the stronger the association with cancer. In one study of more than 900,000 adults, the death rates from all cancers combined were 52 percent higher in men and 62 percent higher in women who were classified as severely obese. In another study, obesity links were found in an estimated 51 percent of women and 14 percent of men with newly diagnosed cases of cancer. The studies also show a higher recurrence rate after radical prostatectomy for prostate cancer in obese men and an incidence rate of 50 percent and decreased survival rate in obese women with postmenopausal breast cancer.
By applying the levels of overweight and obesity, Graham Colditz, a physician with the Harvard School of Public Health, estimated the number of cancer cases that could be avoided if no one were overweight or obese. His estimates of avoidable cancer cases included 49 percent of endometrial cancers, 39 percent of esophageal cancers, 31 percent of kidney cancers, 20 percent of non-Hodgkin lymphoma cases, 17 percent of multiple myeloma cases, 14 percent of pancreatic cancers, 14 percent of colon cancers, and 11 percent of breast cancers.
Symptoms: There are no symptoms that are specific to obesity-associated cancers.
Screening and diagnosis: Screening for obesity-associated cancers includes annual physical examinations to calculate BMI and take waist measurements as well as annual laboratory tests, such as serum lipid panel, fasting glucose level, and thyroid function tests. In addition, people can essentially screen themselves by monitoring their own weights. There are no specific tests for obesity-related cancers; testing is done when patients exhibit other symptoms. Staging is specific to the type of cancer that develops.
Treatment and therapy: Treatment for obesity-associated cancer is specific to the type of cancer. However, based on data obtained during various studies, patients must also reduce their weight to avoid the increased risk that obesity places on successful treatment. Patients must set weight-loss goals and obtain assistance from a registered dietitian or weight-loss program for in-depth counseling. Many reputable commercial and community programs exist for obesity treatment. Desirable programs should include diets that meet the United States recommended daily allowance for nutrients, exercise counseling, behavior modification, and provision for long-term maintenance.
The National Institutes of Health guidelines suggest nonpharmacologic treatment for six months and then consideration of weight-loss medication if weight loss is unsatisfactory in those with a BMI greater than 30 or a BMI greater than 27 with associated risk factors. Patients with severe obesity (BMI greater than 40) may also be considered for gastric bypass or gastroplasty procedures.
Prognosis, prevention, and outcomes: Long-term maintenance of weight loss is extremely difficult. If the patient is not motivated, successful weight loss is unlikely. Obesity can be prevented by educating children and adults in healthy dietary habits and exercise requirements, but only if individuals choose to follow the guidelines and do not have physical causes for the excess weight. Weight reduction can have a significant impact on a person’s risk for developing obesity-associated cancers.
"Body Weight and Cancer Risk." Cancer.org. Amer. Cancer Soc., 30 Jan. 2013. Web. 30 Oct. 2014.
Calle, E. E., et al. “Overweight, Obesity, and Mortality from Cancer in a Prospectively Studied Cohort of U.S. Adults.” New England Journal of Medicine 348.17 (2003): 1625–38. Print.
Fryar, Cheryl D., Margaret D. Caroll, and Cynthia L. Ogden. Prevalence of Overweight, Obesity, and Extreme Obesity among Adults: United States, Trends 1960–1962 through 2009–2010. Natl. Center for Health Statistics, Centers for Disease Control and Prevention, September 2012. PDF file.
Giovannucci, E., and D. Michaud. “The Role of Obesity and Related Metabolic Disturbances in Cancers of the Colon, Prostate, and Pancreas.” Gastroenterology 132 (2007): 2208–25. Print.
Masters, Ryan K., et al. "The Impact of Obesity on US Mortality Levels: The Importance of Age and Cohort Factors in Population Estimates." American Journal of Public Health 103.10 (2013): 1895–1901. PDF file.
"Obesity and Cancer." Cancer.gov. Natl. Cancer Inst., Natl. Inst. of Health, 3 Jan. 2012. Web. 30 Oct. 2014.
Ogden, Cynthia L., Margaret D. Carroll, Brian K. Kit, and Katherine M. Flegal. "Prevalence of Childhood and Adult Obesity in the United States, 2011-2012." JAMA: The Journal of the American Medical Association 311.8 (2014): 806–14. PDF file.
Polednak, A. P. “Trends in Incidence Rates for Obesity-Associated Cancers in the U.S.” Cancer Detection and Prevention 27 (2003): 415–21. Print.
No comments:
Post a Comment