Abstract
Growing evidence suggests that overweight/obesity and physical inactivity are important targets for cancer prevention and control. The International Agency for Research on Cancer estimates that “25% of cancer cases worldwide are caused by overweight or obesity and a sedentary lifestyle.” U.S. studies have attributed one in five cancer deaths in women, and one in seven in men, to obesity. Regular physical activity has been associated with lowered cancer incidence by 10% to 50% across many types, including breast, colon, endometrial, and lung. It is difficult in most epidemiological studies to disentangle the contributions of sedentariness, physical inactivity, and obesity to cancer risk. However, physical activity clearly exerts its protective influence both directly, for example, by decreasing gastrointestinal transit time, consuming calories needed for tumor growth, improving immune system functioning, and/or postponing pubertal development, and indirectly, by decreasing fat stores, favorably altering fat distribution and preventing weight gain.
This presentation provides a brief overview of existing research on physical activity intervention in underserved populations in which cancer burden is concentrated, and a discussion of factors associated with such interventions. Because the literature on obesity treatment in adulthood is extensive and beyond the scope of this presentation, emphasis will be placed on physical activity promotion and the prevention of weight gain. Physical activity intervention studies in adults have generally demonstrated statistically significant but modest outcomes. Comprehensive intervention designs combining individual-level and physical environmental changes have posted the largest effect sizes, as have those targeting dietary and activity behaviors. Emerging models have incorporated sociocultural environmental changes with promising results, particularly in integrating short bouts of physical activity into organizational routine.
Research including or targeting underserved populations poses unique challenges at each stage of the intervention process: design, recruitment, implementation, and evaluation. Effective approaches to address these challenges have included such strategies as community involvement from study inception, direct communication about historical exploitation and overlap of researcher and community goals, oversampling to ensure adequate power for subgroup analyses by ethnicity, provision of meaningful incentives and logistical support, and using study designs that benefit control group members.
The real primary cancer prevention opportunity lies in obesity prevention and physical activity promotion in childhood. Findings from interventions in youthful populations are similar to those in adults. Structural interventions may produce modest improvements in BMI progression and risk behaviors in certain sub-samples of students, particularly in low-resource school environments. Opportunities to demonstrate significant effects may actually be greater in settings or populations with very low baseline rates of fitness-promoting behaviors and conditions. However, these interventions were no more successful in addressing established obesity than conventional clinical treatment approaches. Comprehensive interventions aimed at both physical (in) activity and eating were more consistently effective in preventing obesity than were single-focus ones. There is also evidence for the feasibility and effectiveness of augmenting conventional activity opportunities (physical education and recess) with short intervals of physical activity to aid in obesity prevention, particularly in light of their minimal cost, ready adaptation to school routine and benefits for outcomes of interest to educators. Despite a number of inherent limitations, individually targeted interventions have a major role in obesity control in youth, many of whom experience intractable obstacles of poverty and low-resource schools, and have more severe levels of obesity and obesity comorbidities requiring aggressive and long-term approaches. While appropriate choice of location and setting are crucial to intervention recruitment, attendance, and retention, the mere fact that they require active attendance (rather than offering the possibility of passive exposure as in environmental interventions) deters the participation, leading to power and generalizability constraints. This is particularly true for low-income groups who confront myriad logistical challenges such as childcare, transportation and work scheduling. In addition, individual interventions are expensive, resource- and labor-intensive, and less capable of engaging large samples of participants.
Obesity may best be prevented by addressing environments both within schools and those proximal to and interfacing with schools (corner stores, fast food restaurants, and after-school programs), and local governments may play a central role in coordinating these efforts. Surveillance must be enhanced to permit better targeting of intervention efforts and assessment of intervention effects, and scientific journals must enforce reporting of sample demographics, at least by gender and either race/ethnicity, or socioeconomic status (SES) in geographic areas with few ethnic minority groups. Ethnic minority populations are not monolithic, and their heterogeneity must be recognized. Clearly gender is a major factor in intervention development and adaptation, but SES, region of residence, and family regional or national origins (e.g., Southern United States, Caribbean, African immigrant) are also important. Earlier intervention may be necessary in order to attenuate the incidence of obesity, and emerging work in childcare and other infant and toddler services is critically needed.
Clearly the environments of minority and low-income children are less conducive to healthy eating and physical activity than those of white or affluent groups. Social and political disadvantage are reflected in food availability, food advertising, school policies, and access to recreational facilities and other physical activity. The effective cost, economically and behaviorally, of healthy eating and active living is higher and the feasibility lower, in low-income or ethnic minority communities compared to others.
People with the most limited choices are also the most constrained by their immediate environments. This could mean that changes in the environment would have a greater payoff for the highest risk populations and, indeed, this has been demonstrated in some instances as noted earlier. On the other hand, to the extent that people—particularly in populations undergoing chronic ecological stress—have adapted to their circumstances, isolated environmental changes cannot be expected to break longstanding eating and physical activity patterns conditioned by functioning and survival in generally adverse contexts. This is especially relevant when the very attitudes and behaviors targeted for change are those identified with heavily commercially marketed social status or prestige, important traditions, or emotional satisfaction. Cars are status symbols, with public transportation or walking only for those who can't afford cars. Being able to treat your children to a meal at a popular fast food restaurant may be more meaningful to parents who have to work harder to afford this. Getting enough rest to recover from the stresses of the day may be seen as more important than going out to exercise. Large heavy meals at church or celebrations may form the core of family or social interactions. High-fat and high-calorie “soul foods,” for example, although part of the legacy of slavery, have taken on positive cultural connotations and help to define African American ethnic identity. In addition, some health advice perceived as coming from the majority culture may be met with distrust generalized from experiences with discrimination in other realms.
Promoting physical activity in underserved communities is essential to improving population-level cancer outcomes. There are key opportunities for achieving population wide increases in physical activity and diminution of weight gain by targeting worksites, schools and other settings, with their captive audiences and organizational assets useful in influencing behavior, e.g., social support and norms. Additional resources are becoming available to aid in the promotion of physical activity and obesity prevention in underserved groups, including federally and foundation-supported research networks, disparities elimination projects and pipeline programs to cultivate “cultural insider” researchers. In particular, unique and unprecedented visibility and attention to finding solutions to these disparities is arising from the prevention funding in the health care reform legislation and the American Recovery and Reinvestment Act (ARRA), and First Lady Michelle Obama's campaign to end childhood obesity within a generation. The time is ripe for meaningful intervention.
Citation Information: Cancer Epidemiol Biomarkers Prev 2010;19(10 Suppl):ED02-03.
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