Area-level socioeconomic status and cancer outcomes: Is there an association and can it be explained by behavior?
Hastert, Theresa A.
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Increasingly, area-level socioeconomic status (SES) is recognized as an important predictor of health outcomes and health behaviors independent of individual-level socioeconomic characteristics; however, associations between area-level SES and cancer outcomes are not well understood. Ecologic evidence suggests a relationship between area-level socioeconomic status and cancer incidence and mortality; however, fewer studies have included measures of individual socioeconomic status to assess whether observed associations are due to the compositional effect of the individuals living within the areas of interest. Little is known about individual-level behaviors or risk factors that may explain the pathways through which area-level socioeconomic factors could affect cancer risk. In an effort to summarize risk behaviors that affect cancer risk, the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) published eight recommendations related to body weight, physical activity and dietary behaviors aimed at reducing cancer incidence worldwide, based on a comprehensive review of the literature related to common cancers. However, the reduction in total and site-specific cancer risk and cancer mortality associated with adhering to these guidelines is unknown. Using data from the VITamins And Lifestyle (VITAL) cohort study, including 77,719 adults aged 50-76 at baseline in 2000-2002 and living in the 13 counties of the Western Washington Surveillance, Epidemiology and End Results (SEER) cancer registry, we examined whether meeting the WCRF/AICR cancer prevention recommendations related to body fatness, physical activity, energy density of the diet, fruit and vegetable intake, consumption of red and processed meats and alcohol use was associated with reductions in total cancer mortality. We further used data from the 2000 U.S. Census to develop an area-level SES index for the block group of residence of each VITAL participant to examine whether area-level SES is associated with total and site-specific cancer incidence and cancer mortality. Finally, we examined whether and to what extent individual modifiable risk factors including the WCRF/AICR recommendations examined plus cancer screening and pack-years of smoking explained the observed association between area-level SES and cancer mortality. Each additional WCRF/AICR recommendation met was associated with a 9% reduction in total cancer mortality (hazard ratio (HR): 0.91, 95% confidence interval (CI): 0.87, 0.96) among participants with no history of cancer at baseline. Meeting at least five recommendations was associated with a 60% reduction in cancer mortality compared with meeting no recommendations (HR: 0.40, 95% CI: 0.25, 0.62). These associations were similar among men and women and among participants older and younger than 65 years at baseline, but the association was somewhat stronger among non-smokers (HR per recommendation: 0.85, 95% CI: 0.78, 0.93) than among ever-smokers (HR: 0.94, 95% CI: 0.88, 1.00; Ptrend = 0.091). After controlling for age, sex, race/ethnicity, and marital status, living in areas in the lowest quintile of area-level SES was associated with increased lung cancer incidence (HR: 2.21, 95% CI: 1.69, 2.90) and colorectal cancer incidence among men (HR: 1.75, 95% CI: 1.14, 2.70) and total cancer mortality (HR: 1.68, 95% CI: 1.47, 1.93) compared with living in areas in the highest quintile of area-level SES. Further controlling for compositional factors including individual education and household income weakened but did not eliminate these associations (HR for lung cancer: 1.43, 95% CI: 1.07, 1.91; HR for colorectal cancer: 1.53, 95% CI: 0.99, 2.38; HR for cancer mortality: 1.28, 95% CI: 1.11, 1.48). Among participants with no history of cancer at baseline, living in areas in the lowest quintile of area-level SES was associated with 77% higher cancer mortality than living in areas in the highest quintile of area-level SES (HR: 1.77, 95% CI: 1.50, 2.11). Adding individual-level modifiable risk factors into the models reduced the observed association by 45% (95% CI: -72%, -15%). In models further controlling for individual education and income, area-level SES remained associated with cancer mortality (HR for highest- vs. lowest-SES areas: 1.37, 95% CI: 1.14, 1.65) and adding modifiable risk factors reduced the association by 37% (95% CI: -93%, 22%). Smoking, screening and physical activity explained the largest proportion of the association in both models. Adherence to the WCRF/AICR cancer prevention recommendations developed to reduce incidence of common cancers could substantially reduce cancer mortality. Living in low-SES areas is associated with increased lung cancer incidence, increased colorectal cancer incidence among men, and higher total cancer mortality. These associations are largely, but not completely, explained by individual education and income. The association between area-level SES and cancer mortality is also partially explained by behavior, particularly smoking, physical activity, and screening; but area-level SES remains associated with cancer mortality after accounting for individual SES and behaviors, suggesting a possible contextual effect of area-level SES independent of these factors.
- Epidemiology