Solid evidence suggests that population screening can substantially reduce the incidence of colorectal cancer and mortality from the disease,2–8
yet rates of CRC screening continue to be surprisingly low. Obesity, which is associated with a higher incidence of colorectal cancer11–18
and a higher mortality from the disease,19,20
could be an important clinical marker of the need for screening. Nevertheless, we found statistically significantly lower rates of colorectal cancer screening among one important group of patients at increased risk—morbidly obese women. Although small, this difference in the screening rate for morbidly obese women compared to others persisted despite adjustment for other potentially important confounders. The lower screening rate was apparent only among morbidly obese women. We found no differences in colorectal cancer screening among overweight or obese women compared to women with a normal BMI. We also did not observe BMI-related differences in colorectal cancer screening among men.
As noted in other studies,9,10,35,36
overall colorectal cancer screening rates fall well below national guideline-recommended targets.37
Ours is the first study to examine the association between BMI and colorectal cancer screening and the only study to examine the impact of BMI on rates of cancer screening among men. Prior research demonstrating that obese women were less likely than nonobese women to receive cancer preventive services22–24
focused on screening for cancers other than colorectal cancer and did not include men. Prior national studies have shown that women have lower rates of colorectal cancer screening than men,38
while state-based studies have not found consistent gender-related differences in CRC screening.36,39
Past studies suggest, however, that women are more likely than men to get FOBT and less likely to receive sigmoidoscopy.10,36,38
Future studies may help clarify whether the impact of BMI on preventive services is limited to women and whether it extends to the use of other preventive services.
We found a “threshold” relationship between BMI and CRC screening rates, with a significant effect of BMI on screening of morbidly obese women but no effect of BMI on screening rates for women who would be classified as overweight or obese. Other researchers have found a similar threshold effect of BMI on the rate of pelvic examinations. Among women, only those with the highest BMIs are significantly less likely than others to receive pelvic exams.24
In two other studies, rates of breast and cervical cancer screening were lower for women with higher BMI, but there was not a clear threshold at which lower screening rates were apparent.22,23
The causes of lower screening rates among obese individuals remain elusive. However, our finding of gender-related differences in the association between BMI and CRC screening may shed light on some of the factors that contribute to screening disparities. Obesity-related disparities may result from patient factors, physician factors, or their interactions. Patient-related factors may include poorer access to care (perhaps mediated by lower socioeconomic status40
or ability to pay) or increased reluctance among obese individuals to undergo screening.24
The obese individuals in this sample were of a lower socioeconomic status and more likely to be uninsured regardless of gender. However, in our study, these factors did not account for the difference in screening rates we observed.
Physician-related barriers to screening may include a perceived increase in the technical difficulty of the procedures, the competing demands of managing other clinical comorbid conditions41,42
such as hypertension or diabetes, or physician bias against obese patients.24,43–47
Greater technical difficulty seems less likely to explain our results. Procedures should be equally challenging among morbidly obese men and women, suggesting that the BMI-related differences should be similar for men and women, but we found no BMI-related difference in screening rates among men. Likewise, both men and women who are obese tend to have more competing comorbid conditions,48
arguing against comorbidity as the cause of BMI-related disparities in screening. Further, sigmoidoscopy may pose more technical difficulty in obese patients but FOBT should not, yet we found lower rates of both procedures among morbidly obese women. The gender and BMI interaction we observed is consistent with prior research suggesting that bias and stigmatization related to obesity may be more severe for women than for men.40
Patient reluctance to undergo screening and physician reluctance to recommend or encourage screening for morbidly obese women may reinforce one another in contributing to decreased screening in this high-risk population.24
Our study has some limitations. Our measures of colon cancer screening and BMI are based on self-report. Prior research has shown a high correlation between self-report and chart audit for FOBT and sigmoidoscopy.49,50
Weight, however, tends to be increasingly underreported as BMI increases,51
but systematic underestimation of BMI among the most obese individuals would bias our findings toward the null. Past research, however, suggests a high reliability and validity of self-reported height and weight in the BRFSS.52
There is a possibility that not all of the respondents in our sample were eligible for CRC screening. Persons with decreased life expectancy or other contraindications to screening might not be identified; however, we would expect these numbers to be small. The BRFSS is a telephone-based survey and may only be generalizable to the 94% of the noninstitutionalized U.S. population with telephones.53
The BRFSS only asks a single question that combines colonoscopy and sigmoidoscopy and does not include a question about screening with barium enema, making it possible to misclassify as unscreened individuals who had actually received a barium enema or a colonoscopy 5 to 10 years earlier. Our study was not designed to identify all of the mediators of BMI-related disparities. Future studies are needed to understand other barriers to CRC screening and the best practices to increase screening among morbidly obese women.
In summary, our results show that colorectal cancer screening rates are disturbingly and persistently low in the United States. Our results are an important demonstration of an easily measured marker of increased disease risk (BMI) that primary care clinicians should consider in targeting vulnerable populations for screening. Yet, morbidly obese women, who are at increased risk of developing and dying from colorectal cancer, appear less likely to receive screening than others. General efforts to boost CRC screening rates are clearly needed, and our results suggest that special efforts to increase screening of morbidly obese women may be important. Future studies should explore the reasons morbidly obese women are less likely to be screened than others. Such information could be highly useful in designing strategies to increase screening of the general population, while eliminating the disparity identified by our study.