This systematic review demonstrates an inverse relationship between class I, II, and III obesity and recent mammography that was statistically significant for class III obesity. Compared to their lean counterparts, women with class III obesity were 20% less likely to report recent mammography. In white women, we found a statistically significant negative association between class II and III obesity and being up-to-date with mammography. We did not find this association between BMI and mammography among black women.
Two of the three studies that did not report an inverse association between recent mammography and increasing BMI were not nationally representative. One was a chart review from family practices in New Jersey with primarily non-white patients40
, and the other was a Harlem survey among mostly non-Hispanic blacks42
. The findings of these two studies are consistent with the results of our meta-analyses in which we observed no significant inverse relationship between obesity and mammography in non-whites. The third negative study41
included women <40 years of age. These results may be confounded by age since younger women are more likely to have a lower BMI54
and to report a lower prevalence of mammography since it is not routinely recommended for them.
Obese women may experience several possible barriers to mammography. Prior data show that obese women may delay medical care55
because of poor self-esteem and body image, embarrassment29,30,55,56
, a perceived lack of respect from health-care providers, or to avoid unwanted weight loss advice28
. Obesity may be a marker for sub-optimal health behavior in general, of which lack of mammography is simply one facet30,33
. Also, beliefs regarding cancer screening may vary by BMI33
. There could be physical limitations to obtaining mammography for obese women, but obesity is associated with a higher content of fat in the breast tissue that actually increases the sensitivity of mammography for detecting breast cancer57,58
. Finally, obesity is associated with lower socioeconomic status59
, which may decrease access to preventive care.
There are also many physician-related factors that may decrease screening mammography among obese women. Obesity-related co-morbid conditions may hinder referral for purely preventive services41,60,61
. In addition, providers have reported difficulty and inadequate resources and education in providing care for obese women28
. Finally, physicians may have biases against obese women, resulting in less screening62–64
Obesity did not appear to affect the report of recent mammography in black women. This may be due to racial differences in obesity-related body image65–67
. In particular, it has been reported that overweight or obese white, but not black, women were more likely to feel worthless, which may impact willingness to undergo mammography32
. Black women may have a similar risk of developing breast cancer68,69
, but higher breast cancer mortality21,68–71
. They tend to present with a higher stage of breast cancer69,71
, which has been linked to (1) less follow-up for abnormal exams72
, (2) higher rates of obesity72–75
, (3) socioeconomic factors76
, (4) cultural beliefs (e.g., belief in herbal treatments)76
, and possibly, lower likelihood of screening77–79
, although this is controversial68,80–82
. Our findings, the first meta-analyses by race, suggest that rates of mammography in black women do not vary significantly by BMI.
We included only 6 of 17 studies in our meta-analyses based on the provision of unique nationally representative data and BMI in five standard categories. However, 14 of the 17 studies reported a negative association between BMI and report of mammography. Also, we obtained similar results when we included all nine studies that reported BMI in five standard categories.
Most of the included studies were cross-sectional and cannot establish causality, but it is unlikely that failure to undergo mammography would contribute to weight gain. Also, we relied on the use of observational studies, which are susceptible to residual and unmeasured confounding. In particular, socioeconomic factors and health behaviors may confound the relationship between obesity and breast cancer and are difficult to account for fully. Although we did not find publication bias, we had limited power with a small number of studies. However, our search also included articles in which body weight was not the primary exposure, and thus, the potential for publication bias should be low.
The included studies used self-report of BMI as the measure of body weight, which has several limitations: It may underestimate obesity, especially in women83
, but may also overestimate obesity, especially in blacks83
. Self-report of height and weight may differ by survey type (telephone versus in-person), age, and BMI84
. Overall, the included studies may have placed more obese participants into less obese categories, which would bias our results toward the null or result in finding an inverse association in overweight or milder obesity. However, the overall qualitative association between body weight and mammography would be unchanged.
Most of the included studies also relied upon self-report of mammography. A recent meta-analysis found that self-report of mammography had a sensitivity of 93% and specificity of 62%85
. While this study reported similar sensitivities for self-reported mammography in blacks and whites, the specificity of self-reported mammography was only 49% among blacks85
. Thus, mammography results are likely inflated above their actual rates with the degree of inflation higher for blacks. There is no evidence that the accuracy of self-report of mammography varies by BMI, but if it does, our results would also be biased.
The included studies did not stratify on menopausal status, but only one study included women under the age of 40 years41
. It seems unlikely that menopausal status would affect willingness to be screened in women over age 40. While the relationship between obesity and premenopausal breast cancer risk and mortality is unclear10–12
, obesity increases postmenopausal breast cancer risk10,11,13–15
Finally, our search strategy may have been susceptible to selection bias given that we included a small number of full articles from the total citations reviewed, we manually searched only 11 key journals, and we had limited success obtaining full results from contacted authors. However, the qualitative results matched our meta-analytic results, we included no new articles from the manual search of 11 journals, and we were very sensitive in promoting a title or abstract to full article review (i.e., if an article discussed risk factors associated with mammography, we promoted that to full article review). Additionally, we re-reviewed a random sample of 2.5% of the full articles excluded at title review and 5% of the full articles excluded at abstract review and did not find any additional articles that satisfied our inclusion criteria.
Our study also has several strengths. This is the first systematic review with meta-analyses exploring the relationship between obesity and mammography and the only one to examine the effect of race on this association. We comprehensively searched multiple electronic databases in addition to manual searching. Also, we contacted authors for data leading to additional results from four studies. Finally, the meta-analyses were based on nationally representative surveys and thus are generalizable to the US population.
The main implication of our study is that a lack of routine screening mammography may explain some of the increased breast cancer mortality in obese postmenopausal women. Clinicians should be aware of this disparity in evaluating their own practices. Future research should determine why obese women are less likely to report recent mammography, including the investigation of a lack of health care access due to perceived bias or lack of insurance as a possible cause and explore whether there are consistent differences by race.