Obesity is clearly associated with an increase in cancer morbidity, but its correlation with screening rates is more complicated. Obesity has been linked to higher rates of some cancer screenings, such as prostate cancer, and associated with lower rates of others, such as cervical cancer screening, according to a review of published literature appearing in the January issue of the Journal of Obesity.

"Numerous studies have suggested that obesity constitutes an obstacle to cancer screening, but a deeper examination also considering the role of race/ethnicity and gender in the equation has not been done before," said Heather Bittner Fagan, MD, associate professor at Thomas Jefferson University in Philadelphia. "A greater understanding of the relationship between cancer screening and obesity, race/ethnicity and gender can also help explain the association between obesity and increased cancer mortality."

Results varied based on the type of screening and between ethnicities. Lower rates of cervical cancer screening with Pap smear, for example, were consistently associated with increasing weight in 12 studies examined by the researchers. In five of the studies which looked at the association among white women, all reported a negative association, while only two of six studies which looked at black women found a negative association.

Prostate cancer screening levels, on the other hand, were consistently shown to increase with weight across all races and ethnicities.

"This could be explained by differences in access and utilization of healthcare; as weight increases so do other comorbid conditions, making heavier men higher users of healthcare and perhaps more encouraged to be tested by their healthcare providers," wrote Richard Wender, MD, professor at Jefferson Medical College of Thomas Jefferson University and chair of family and community medicine at Thomas Jefferson University Hospital, both in Philadelphia.

In total, weight did not correlate with breast cancer screening, according to the three studies examined, though some differences were present when results were stratified by race. One study showed obesity corresponded with decreased mammography use in white women and increased use in black women, while another study showed no effect.

Colorectal cancer (CRC) screening is the only cancer screening recommended for both men and women, and here gender appears to play a role in whether obesity affects screening rates.

“These studies suggest that body weight may have a different impact on the likelihood of undergoing CRC screening in men and women,” wrote the authors. “In women, the majority of the literature suggests a negative association between obesity and CRC screening, whereas in men there is little consistency in the association of obesity and CRC screening.”

Cultural differences among men, women, blacks and whites as well as socioeconomic factors such as insurance status and access to healthcare, which can be confounded with race/ethnicity and gender, may limit or grant access to certain cancer screenings.

"Screening behaviors can vary by ethnicity/race and gender, but more research is needed to create a comprehensive understanding of obesity and cancer screening in race-gender subgroups such as white men, white women, black men and black women, accounting for the effects of the doctor-patient relationship, access to care and type of screening test," wrote Fagan and Wender.

Obesity is second only to tobacco use as a risk factor for cancer and is associated with increased mortality for all cancer combined as well as for cancer of specific sites, including cancer of the colon/rectum, prostate, breast and cervix.