Negative link between obesity and colon cancer screening in white women

Johns HopkinsApr 5 2012

A new study by Johns Hopkins researchers shows that obese white women may be less likely than normal-weight counterparts and African-Americans of any weight or gender to seek potentially lifesaving colon cancer screening tests.

Results of this study follow the same Johns Hopkins group's previous research suggesting that obese white women also are less likely to arrange for mammograms, which screen for breast cancer, and Pap smears, which search for early signs of cervical cancer.

"No group is perfect when it comes to screening, and overall rates of colonoscopy are low, but if you're obese, female and white, our data show you're probably even less likely to be screened," says study leader Nisa M. Maruthur, M.D., M.H.S., an assistant professor in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine.

Maruthur notes that the reluctance to be screened is especially serious in this group because obesity is linked to higher risk for colon cancer and an increased risk of death from the disease.

"Being concerned about your weight usually is good, but here it appears to be keeping people from a test we know saves lives," she says. "Obese white women may avoid screening because they feel stigmatized and embarrassed to disrobe for the tests."

Despite evidence of the value of colonoscopy — a procedure that sends a flexible tube with a camera into the bowel to search for and guide removal of precancerous polyps and other tumors — only 20 percent of women and 24 percent of men over the age of 50 undergo the test, which is recommended by the United States Preventative Services Task Force for everyone between the ages of 50 and 75 on a periodic basis.

Another suggested test, fecal occult blood testing, which searches the stool for hidden blood that can be another sign of colon cancer, is also underused, with just 12 percent of American men and women using it.

Preventive care researchers have long tried to better understand barriers to colon cancer screening. Preparatory laxatives, anesthesia, fear of discomfort and embarrassment are known to discourage many.

In the new study, described in the journal Cancer, Epidemiology, Biomarkers and Prevention, the Johns Hopkins researchers added evidence that for white women, obesity appears to have a negative impact on screening rates. There was a hint in the data that the same may be true for obese white men, but Maruthur said research is needed to verify the suggestion.

Negative body image among obese white people may explain this association, which seems to be fostered particularly in white women, where the pressure to be thin appears to be more intense, Maruthur says. In an unrelated study she cited, for example, white and African-American women rated magazine images of "thin, average-weight and large" African-American and white women. White women rated large white women lower in interpersonal and career domains, while African-American women did not stigmatize large African-American women in this way.

Maruthur says if further studies confirm the negative relationship between obesity and screening in white women, outreach and education programs can be shaped to overcome it.

Maruthur says another barrier to screening among obese people may be their tendency to have higher rates of pressing health concerns, leading physicians to delay or put off discussions of preventive screening. However, the rates of those medical conditions are not likely higher for obese whites.

In the new study, Maruthur and her colleagues reviewed the medical literature and delved into data from 23 published studies that included information on body mass index (BMI) and colon cancer screening rates. BMI is a measure of body fat based on height and weight that applies to adult men and women. A BMI between 18.5 and 24.9 is considered normal weight, between 25 and 29.9 is considered overweight and 30 or greater is considered obese.

While overall, the researchers found no link between higher BMI and lower rates of colon cancer screening, they did find the association in a subgroup of white women with a BMI between 30 and 34.9. They were 13 percent less likely to be screened when compared with normal-weight counterparts. Women who were the most obese — with a BMI of 40 or higher — were 27 percent less likely to be screened.