Physical activity as a mediator linking neighborhood environmental supports and obesity in African Americans in the path trial.

Obesity is a leading cause of morbidity and mortality in the United States. More than 30% of adults are obese, with African Americans disproportionately represented (Flegal, Carroll, Kit, & Ogden, 2012). Despite evidence that regular engagement in physical activity (PA) may prevent the development of overweight and obesity (Brock et al., 2009), most adults in the United States do not meet national recommendations for PA (Troiano et al., 2008). Lack of regular PA is particularly evident among African American adults (Prus, 2007). To address disparities in obesity, it is a public health priority to identify factors that promote higher levels of engagement in PA in African Americans. In the present study, a bioecological framework was used to identify factors that are associated with positive health behaviors. This approach posits that health behaviors are influenced by conditions in the social and physical environment, in addition to individual factors (Bronfenbrenner, 1979; Bronfenbrenner & Ceci, 1994; McLeroy, Bibeau, Steckler, & Glanz, 1988; Spence & Lee, 2003). Indeed, accumulating evidence has indicated that environmental and social factors are important for promoting PA (Sallis et al., 2009; Trost, Owen, Bauman, Sallis, & Brown, 2002). These factors may be particularly important in underserved African American adults who experience limited access to health-promoting contexts and services (Gordon-Larsen, Nelson, Page, & Popkin, 2006). Further, similar environments may have different health impacts for African Americans than for other racial and ethnic groups (Hooker, Wilson, Griffin, & Ainsworth, 2005). The present study expands on a limited literature that examines the association of environmental and social factors with PA in under-served African American adults, and tests whether PA is a potential mechanism linking these factors with obesity. One aspect of the environment that has received increased attention over the past decade is neighborhood walkability. Two features related to neighborhood walkability that have been shown to be consistently associated with PA in predominantly nonminority samples are infrastructure for walking (e.g., sidewalks, trails) and access to services within walking distance (Owen, Humpel, Leslie, Bauman, & Sallis, 2004; Sallis et al., 2009). Studies with ethnically diverse samples have also found associations between these neighborhood features and PA (Addy et al., 2004; King et al., 2005; Parks, Housemann, & Brownson, 2003). A limited number of studies have examined associations between the neighborhood environment and PA in African American adults, yielding inconsistent findings, but providing some support for the importance of neighborhood walkability for PA in this population (Casagrande, Whitt-Glover, Lancaster, Odoms-Young, & Gary, 2009). For example, some studies have found associations between features of neighborhood walkability (such as infrastructure for walking) and PA in African Americans, including engaging in recommended levels of PA and leisure-time PA (Ainsworth, Wilcox, Thompson, Richter, & Henderson, 2003; Heinrich et al., 2007); however, other studies have not (King et al., 2000; Rohm Young & Voorhees, 2003; Sanderson et al., 2003). Another neighborhood feature—crime—has been frequently cited as a barrier to PA in qualitative studies (Eyler et al., 1998; Holman, Donovan, & Corti, 1996). However, quantitative evidence of this association has been mixed in both predominantly nonminority samples (Foster & Giles-Corti, 2008) and African American adults (Casagrande et al., 2009). Whereas some studies have found an association between crime and PA in minority samples, including African Americans (Addy et al., 2004; Eyler et al., 2003; Hannon, Sawyer, & Allman, 2012; Wilbur, Chandler, Dancy, & Lee, 2003), other studies have not (Bennett et al., 2007; Hooker et al., 2005; King et al., 2000; Rohm Young & Voorhees, 2003; Sanderson et al., 2003). Nonetheless, because safety concerns have been identified as a barrier to PA in qualitative studies, crime warrants further investigation, particularly in underserved African Americans. Social support, defined broadly as resources and encouragement provided by others, has also been identified as an important correlate of PA (Trost et al., 2002). Social support can come from different sources, including family and friends, and can take various forms, including instrumental and tangible (e.g., direct assistance), informational (e.g., PA suggestions), and emotional (e.g., encouragement) support (Harley et al., 2009). The few studies that have examined associations between social support and PA in African Americans have suggested the importance of social support for PA, but findings have been inconsistent. For example, although there is some evidence that family support is particularly important for PA in African Americans (Komar-Samardzija, Braun, Keithley, & Quinn, 2012), other studies have found support provided by friends, not family, to be associated with PA in this population (Peterson & Cheng, 2011; Sharma, Sargent, & Stacy, 2005). Moreover, some previous studies have shown that social support provided by either family or friends is associated with PA in African American men (Hooker, Harmon, Burroughs, Rheaume, & Wilcox, 2011) and women (Eyler et al., 1999). Other studies, however, have not found support provided by both friends and family combined to be associated with PA (Bopp et al., 2006; Li et al., 2012). Thus, an understanding of the association between social support and PA remains limited in African American adults. In summary, previous studies have shown that neighborhood walkability and social support are associated with higher levels of PA. However, less is known about these associations in under-served African American adults or about health behaviors, such as PA, as potential pathways through which environmental and social factors may be linked to obesity. Previous research with nonminority populations has provided mixed evidence that PA is a mediator of these associations. One study found that both objective and self-report measures of PA mediated linkages between neighborhood walkability and weight-related outcomes (Van Dyck et al., 2010). Other studies, however, have not found self-reported PA to be a mediator linking perceptions of the environment and social support with self-rated health (Poortinga, 2006a, 2006b). Additional research is needed to identify specific mechanisms that link environmental and social factors with obesity, particularly in underserved African American adults. The purpose of the present study was to examine PA as a potential mediator of associations of neighborhood walkability and social support with obesity in African American adults as part of the Positive Action for Today’s Health (PATH) randomized trial (Coulon et al., 2012; Wilson et al., 2010). Three communities were identified and matched based on U.S. Census information (e.g., crime, PA, poverty, percent minority) and recruited to participate in the 24-month study. The primary aims of the trial were to compare a combined police-patrolled walking and social marketing intervention to a police-patrolled walking only or a walking-only intervention on increasing moderate-to-vigorous PA (MVPA) after 12 months and to examine the maintenance of effects over 24 months. Longitudinal data are not yet available; therefore, cross-sectional data were the focus of this study. Potential pathways through which environmental and social factors may influence obesity were examined by estimating the effects of neighborhood walkability, social support, and PA on body mass index (BMI) in the PATH sample at baseline. It was hypothesized that greater walkability and peer social support would be associated with increased time spent engaging in PA and lower BMI, and that greater PA would be associated with lower BMI. It was further hypothesized that PA would mediate associations of neighborhood walkability and social support with BMI. To better understand PA as a potential mechanism linking these factors with BMI, hypotheses were tested in a primary model, with accelerometry-assessed MVPA as a mediator, and, in secondary models, with self-reported walking and exercise as mediators.