Race differences in mobility status among prostate cancer survivors: The role of socioeconomic status

Abstract

The objective of this paper was to determine whether there were any race differences in mobility limitation among PCa survivors, and understand the impact of socioeconomic status (SES) on this relationship. Data consisted of 661 PCa survivors (296 Black and 365 White) from the Diagnosis and Decisions in Prostate Cancer Treatment Outcomes (DAD) Study. Mobility limitation was defined as PCa survivors who reported difficulty walking a quarter mile or up 1 flight of stairs. Race was based on the PCa survivors self-identification of either White or Black. SES consisted of education level (i.e., less than high school, high school/GED, some college/associate, bachelors, masters/PhD) and annual household income (i.e., less than $50,000; $50,000–$100,000; greater than $100,000). Adjusting for age, marital status, health insurance, Gleason Score, treatment received, and time to treatment, Black PCa survivors had a higher prevalence of mobility limitation (PR = 1.58, 95% CI: 1.17–2.15) relative to White PCa survivors. When adding education and income to the adjusted model, Black PCa survivors had a similar prevalence of mobility limitation (PR = 1.12, 95% CI: 0.80–1.56) as White PCa survivors. The unequal distribution of SES resources between Black and White PCa survivors accounted for the observed race differences in mobility limitation. This work emphasizes the importance of SES in understanding race differences in mobility among PCa survivors.

Introduction

African American men have a higher incidence and death rate of prostate cancer (PCa) than any other racial or ethnic group (Aziz, 2007; Brawley, 2012; Howlader et al., 2016). Although diagnosed at a younger age, African American men tend to present at a later stage of progression of the disease (Aziz, 2007; Brawley, 2012; Howlader et al., 2016). Compared to White men, African American men are more likely to have metastatic disease, and when treated for PCa, lower survival rates (Bellizzi, Mustian, Palesh, & Diefenbach, 2008; Brawley, 2012; Chornokur, Dalton, Borysova, & Kumar, 2011; Eton, Lepore, & Helgeson, 2001; Given, Given, Azzouz, & Stommel, 2001; Lubeck et al., 2001). PCa survival has been linked to health and functional status problems independent of the cancer itself (Litwin et al., 1995; Potosky et al., 1999) and interest in focusing on issues related to quality of life and health-related outcomes has been growing (Deimling, Schaefer, Kahana, Bowman, & Reardon, 2003; Eton et al., 2001; Lubeck et al., 2001). Despite this burgeoning line of research, the studies examining the disparities in mobility status among PCa survivors are virtually nonexistent.

Mobility status represents an indicator of overall underlying health status and age-related decline in physical function among older adults that varies by race (Simonsick et al., 2008; Thorpe, Koster, et al., 2011; Thorpe, Clay, Szanton, Allaire, & Whitfield, 2011). Also mobility status is often considered as a functional limitation—the third stage of the disablement process (Verbrugge & Jette, 1994). This process has been described as a multi-stage pathway beginning with the presence of pathology (i.e., chronic health conditions) and advancing through stages of impairment, functional limitation and, ultimately, disability (Verbrugge & Jette, 1994). Maintaining mobility is an essential component for independence and good quality of life for middle age to older age adults including PCa survivors (Hewitt, Rowland, & Yancik, 2003; Simonsick et al., 2008; Thorpe, Clay, et al., 2011; Thorpe, Koster, et al., 2011). Often defined as reported difficulty walking for one-quarter mile or climbing one flight of stairs (Simonsick et al., 2008; Thorpe, Clay, et al., 2011; Thorpe, Koster, et al., 2011), mobility limitation is an antecedent to mobility disability, which has been associated with adverse health events in older adults (Guralnik, Ferrucci, Simonsick, Salive, & Wallace, 1995; Wolinsky et al., 2007; Wolinsky, Miller, Andresen, Malmstrom, & Miller, 2005). Further, because mobility limitation represents an early stage of age-related decline (Simonsick et al., 2008), there is an opportunity to gain insight into how to prolong mobility limitation for African American and White PCa survivors.

Education and income have been shown to be associated with mobility limitation (Thorpe, Koster, et al., 2011). However, race and socioeconomic status (SES) are often correlated such that it is difficult to tease apart the independent or joint effects of each on health outcomes. Furthermore when examining race differences in mobility limitation, the omission of understanding how education and income influence race differences can lead to spurious conclusions (Thorpe et al., 2014). Prior work examining race differences in disability in PCa survivors fails to consider the impact of SES on race differences in disability (Deimling et al., 2003). Furthermore disability and mobility limitation represent different stages of the disablement process (Verbrugge & Jette, 1994) which are likely to have different relations with race and SES (Thorpe, Koster, et al., 2011; Thorpe, Szanton, Bell, & Whitfield, 2013). As such there is a paucity of research that focuses on race, SES, and mobility among PCa survivors.

Given the increasing number of aged minorities and the increasing number of PCa survivors (Americans, 2016; Howlader et al., 2016; Parry, Kent, Mariotto, Alfano, & Rowland, 2011), a greater focus on understanding race-related disparities in mobility limitation among PCa survivors is needed. The objective of this paper was to determine whether there were any race differences in mobility limitation among PCa survivors, and understand the impact of SES on this relationship. We anticipate that Black PCa survivors would have worse mobility limitation compared to White PCa survivors. However the inclusion of SES variables would eliminate this race difference in mobility limitation.