U.S. cancer statistics document higher incidence rates of most forms of cancer, including cancers of the oral cavity, pharynx, esophagus, stomach, colon, lung, cervix, kidney, liver and prostate, among African Americans than whites, yet reasons for the racial disparity are poorly understood. Blacks also experience poorer survival than whites for nearly all forms of cancer (treating breast cancer that has spread to other sites in the body), so that the disparities tend to be even greater for mortality than for incidence. Mortality rates for both stroke and heart disease are also higher among blacks than whites in the United States.
To date, the limited participation of African Americans in major epidemiologic investigations has made it difficult to identify reasons for these health disparities. Blacks comprise <5% of many prominent follow-up studies and intervention studies. In the 1990s, two large cohort studies were initiated with higher representation of African Americans: the Multiethnic Cohort Study, drawn from population-based samples in California and Hawaii, has 16% African-American composition (N ~35,000); and the Black Women’s Health Study includes 64,500 black women identified from magazine subscriber lists and professional organizations. Smaller studies of narrower focus have also been launched, such as the Jackson Heart Study, which is following approximately 5,300 African-American men and women in a prospective study in the Jackson, MS area.
Factors associated with low socioeconomic status (SES) (e.g.; poor living conditions, limited access to healthcare services, social stresses, poor health habits) should strongly relate to health outcomes, and it is possible that these factors underlie many of the currently documented racial disparities. To understand the role of socioeconomic disadvantage versus race, studies including low-income adults are needed in order that these factors be investigated in tandem. Enrolling participants across a full spectrum of SES (particularly the lower levels) is challenging, however. The ongoing National Longitudinal Mortality Study (NLMS), a large census-based cohort that through linkage to the National Death Index is examining demographic and socioeconomic differentials in U.S. mortality rates, has the built-in capacity to include all levels of SES but has little or no baseline risk factor or health data.
This manuscript describes the design and implementation of the Southern Community Cohort Study (SCCS), a prospective cohort study designed to identify the underlying reasons for racial disparities in and other chronic disease risk, with the ultimate goal of providing possible avenues for effective interventions and/or preventive strategies. The southeastern United States was chosen as the setting for this study because of its: a) high proportion of long-term African-American residents, b) high proportion of long-term rural residents (another under-studied group), and c) distinctive patterns in both disease occurrence and exposure prevalence. We describe our methodology as well as report on the characteristics of this cohort after 2.5 years of recruitment.