More than one-third of the excess risk of invasive adenocarcinoma of the colon and rectum resulting from low socioeconomic status “could be explained by differences in exposure to behavioral risk factors, particularly a healthy diet,” researchers recently reported in the Journal of the National Cancer Institute.1 The investigators analyzed prospective data on 506,488 participants in the National Institutes of Health–AARP Diet and Health Study, including 7,676 who developed colorectal cancer during follow-up. They then quantified the contribution of behavioral risk factors and obesity, separately and together, to socioeconomic status disparities in colorectal cancer risk.
Body mass index was used to identify patients at unhealthy weight, and dietary patterns were measured using a Mediterranean diet score. Socioeconomic status was measured at the individual level (based on education) and the neighborhood level (based on a multifactor index). Compared with people in high socioeconomic status groups, study participants in low socioeconomic status groups were more likely to have low Mediterranean diet scores and unhealthy weight, and to be physically inactive.
Lifestyle and Cancer Risk
“[Socioeconomic status] differences in prevalence of physical inactivity, unhealthy diet, smoking, and unhealthy weight each explained between 11.3% (body mass index) and 21.6% (diet) of the association between education and risk of colorectal cancer and between 8.6% (smoking) and 15.3% (diet) of the association between neighborhood [socioeconomic status] and risk of colorectal cancer,” the researchers reported. “Health behaviors and [body mass index] combined explained approximately 43.9% (95% CI = 35.1%–57.9%) of the association of education and 36.2% (95% CI = 28.0%–51.2%) of the association of neighborhood [socioeconomic status] with risk of colorectal cancer. The percentage explained by all factors and [body mass index] combined was largest for right colon cancers and smallest for rectal cancers.”
The authors noted that while their findings support recommendations advocating a healthy lifestyle to reduce the risk of colorectal cancer, “as an observational study, our findings suggest but do not definitively prove causal relationships between [socioeconomic status], behavioral factors, obesity, and the risk of colorectal cancer.” ■
1. Doubeni CA, Major JM, Laiyemo AO, et al: J Natl Cancer Inst 104:1353-1362, 2012.