Socioeconomic and behavioral risk factors for mortality in a national 19-year prospective study of U.S. adults
Introduction
Several decades of research conclude that mortality is strongly patterned by a number of sociodemographic variables including gender, race/ethnicity, and residential setting (Adler and Ostrove, 1999, Geronimus et al., 2006, Sorlie et al., 1995). Prior research has also shown that socioeconomic position—meaning the social and economic factors that influence the positions/roles individuals hold within the structure of society, and as measured by education, income, occupational status, and/or wealth—is strongly associated with mortality (Davey Smith et al., 1990, Gerdtham and Johannesson, 2004, Kallan, 1997, Lauderdale, 2001). Across countries, socioeconomic patterns are seen for all-cause mortality and for specific causes of death, including cardiovascular disease and cancer (Faggiano et al., 1997, Fried et al., 1998).
Socioeconomic position is theorized to be a “fundamental cause” of health, whereby higher socioeconomic status confers the intrapersonal, interpersonal, and contextual resources needed to more effectively produce and maintain health over the life course (Adler and Newman, 2002, Phelan et al., 2004). As a fundamental driver of the way in which societies shape health-related exposures and resources, socioeconomic position is purportedly related to mortality risk through multiple mechanisms at both the individual and contextual level. This includes income, wealth, education, occupation, medical care, and other resources that allow people to identify and avoid environmental and personal health risks.
A prominent hypothesis in attempting to explain socioeconomic disparities in mortality is that people of lower socioeconomic position have worse health in large part because they are more likely to engage in risky health behaviors that help people to avoid or reduce these risks (Adler and Newman, 2002, Phelan et al., 2004, Syme, 2008). That is, socioeconomic position produces disparities in knowledge, cognition, exposures, resources and social relationships that in turn lead to different behavior and risk factor profiles across social strata.
Personal health risk factors such as smoking, alcohol abuse, sedentary lifestyle, poor nutrition, and morbid obesity have indeed been found to increase overall mortality risks and to be more prevalent among those of lower socioeconomic position (Flegal et al., 2004, Marugame et al., 2007, Mukamal, 2006, Rehm and Monterio, 2005). However, prior research from longitudinal studies suggests that the higher prevalence of health risk factors in socially disadvantaged populations explains some but not all observed socioeconomic differentials in health status and mortality (Arendt and Lauridsen, 2008, Bassuk et al., 2002; Feinglass et al., 2007, Lantz et al., 1998). In addition, it is not always the case that groups in lower strata have higher rates of health risk behaviors. For example, Rosero-Bixby and Dow (2009) found in a longitudinal study of elderly Costa Ricans that high calorie diets, obesity and hypertension were most prevalent in higher socioeconomic groups.
Although there is a significant amount of prior population-based research regarding the socioeconomic determinants of mortality, there are some limitations in prior work, including research that aims to better understand these phenomena in the United States. First, although there are several longitudinal mortality studies of population-based samples, most have limited generalizability in that they are restricted to a specific age group (e.g., the Health and Retirement Study) or geographic area (e.g., the Alameda County Study) (Feinglass et al., 2007, Frank et al., 2003, Wulsin et al., 2005).
Second, much of the published social epidemiological literature on mortality focuses on one particular social characteristic (e.g. race, education, gender) and/or one cause of death at a time (Meara et al., 2008, Mehrotra et al., 2008, Miller and Wolinsky, 2007, Muntaner et al., 2004, Willcox et al., 2006). This can lead to myopic or even erroneous conclusions about the important drivers of mortality. For example, it is difficult to measure and understand educational disparities in mortality without simultaneously considering income; and a growing body of literature suggests that education and income influence health in related yet different ways (Herd et al., 2007, Zimmer and House, 2003). Nonetheless, many mortality studies focus exclusively on education as a single marker of socioeconomic status (Avendano et al., 2006, Elo and Preston, 1996, Meara et al., 2008).
Third, many studies investigate a broad array of demographic and socioeconomic differentials in mortality but do not include any information on health risk behaviors/exposures or just focus on one factor at a time (Lin, Rogot, Johnson, Sorlie, & Arias, 2003). For example, many of the studies estimating the impact of obesity on mortality risk likely overestimate risk because they do not control for other factors that are strongly correlated with obesity, such as physical activity and socioeconomic status (Freedman et al., 2006, Sui et al., 2007).
Related to the hypothesis that socioeconomic disparities in behavioral risk factors are the driving force behind disparities in mortality, the literature for the U.S. experience is in fact quite limited. The two main studies on this topic that use nationally-representative, longitudinal samples are from the Health and Retirement Study (Feinglass et al., 2007) which focuses on an older population, and an older study from the American Changing Lives Study (Lantz et al., 1998) focusing on mortality between 1986 and 1994.
In this research, we extend prior research from the longitudinal, population-based Americans' Changing Lives (ACL) Study to investigate the interplay between major socioeconomic and behavioral factors that influence individuals' risk of mortality across the life course. Research questions included: 1) what are the demographic and socioeconomic patterns in adult all-cause mortality in the United States between 1986 and 2005 when all are controlled for simultaneously?; 2) to what extent are health risk behaviors related to mortality risk, and do these behaviors explain the observed demographic and socioeconomic disparities in mortality?; and 3) do socioeconomic and behavioral risk factors for mortality vary across younger and older age groups?
This work builds upon and significantly extends prior mortality research using the ACL data from 7.5 years to 19 years of follow-up (Lantz et al., 1998). The main findings include that low income (but not low education or race) remained predictive of mortality when controlling for major health risk behaviors. In addition, the risk of death is not associated with obesity or overweight; and among those age 55 and older at baseline, mortality rates were significantly reduced for those who were overweight or obese. Physical activity—even at relatively low levels—provided a protective effect against mortality. Our results add new and important findings to the extant literature and current public discourse regarding obesity. In addition, our results confirm and strengthen the evidence base of prior findings using a study design with a relatively long follow-up period and a nationally-representative sample.
Section snippets
Study design and sample
Data were from the Americans' Changing Lives (ACL) longitudinal study, which was designed to investigate social patterns of health and aging in the United States. The ACL used a stratified, multistage area sample of non-institutionalized adults age 25 and older residing in the United States in 1986. African Americans and persons age 60 and older were oversampled at baseline. The first wave of data collection (1986) used face-to-face interviews with 3617 subjects, representing a 68% response
Results
The weighted sample at baseline (Table 1) was 52.9% female and 83.5% non-Hispanic white. A significant portion of the weighted sample could be characterized as socioeconomically disadvantaged, with 25.6% reporting less than a high school education and 19.2% reporting a household income of less than $10,000 in the previous year in 1986.
In terms of health risk behaviors at baseline (Table 1), 30.4% reported that they currently smoked, 4.3% were categorized as heavy drinkers, and 14.4% had a BMI
Comment
The Americans' Changing Lives is a nationally-representative, longitudinal study that has data on a broad array of socioeconomic and behavioral risk factors for mortality. The results demonstrate that, for the population of non-institutionalized adults ages 25 + who were living in the U.S. in 1986, the risk of dying over the next 19 years was significantly related to a number of demographic, socioeconomic and behavioral factors. This extends—from 7.5 years to 19 years of follow-up—prior ACL
Acknowledgements
This research was supported by a grant from the National Institute on Aging (R01 AG018418-06). The authors would like to thank Richard Mero and Mary Jo Griewahn for technical support, and Barbara Strane for administrative support. The authors would also like to acknowledge the constructive feedback received from Philippa Clarke, PhD and other members of the Americans' Changing Lives research group, and the thoughtful comments of annonymous reveiwers.
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