The contribution of health behaviors to socioeconomic inequalities in health: A systematic review

Highlights

• Health behaviors are key contributors to the socioeconomic gradient in health.

• Multiple health behaviors contribute more than individual health behaviors.

• Smoking contributes more than alcohol, physical activity, or dietary patterns.

• The contribution of health behaviors varies according to multiple factors.

Abstract

Unhealthy behaviors and their social patterning have been frequently proposed as factors mediating socioeconomic differences in health. However, a clear quantification of the contribution of health behaviors to the socioeconomic gradient in health is lacking. This study systematically reviews the role of health behaviors in explaining socioeconomic inequalities in health.

Published studies were identified by a systematic review of PubMed, Embase and Web-of-Science. Four health behaviors were considered: smoking, alcohol consumption, physical activity and diet. We restricted health outcomes to cardiometabolic disorders and mortality. To allow comparison between studies, the contribution of health behaviors, or the part of the socioeconomic gradient in health that is explained by health behaviors, was recalculated in all studies according to the absolute scale difference method.

We identified 114 articles on socioeconomic position, health behaviors and cardiometabolic disorders or mortality from electronic databases and articles reference lists. Lower socioeconomic position was associated with an increased risk of all-cause mortality and cardiometabolic disorders, this gradient was explained by health behaviors to varying degrees (minimum contribution −43%; maximum contribution 261%).

Health behaviors explained a larger proportion of the SEP-health gradient in studies conducted in North America and Northern Europe, in studies examining all-cause mortality and cardiovascular disease, among men, in younger individuals, and in longitudinal studies, when compared to other settings. Of the four behaviors examined, smoking contributed the most to social inequalities in health, with a median contribution of 19%.

Health behaviors contribute to the socioeconomic gradient in cardiometabolic disease and mortality, but this contribution varies according to population and study characteristics. Nevertheless, our results should encourage the implementation of interventions targeting health behaviors, as they may reduce socioeconomic inequalities in health and increase population health.

Introduction

The existence of a stepwise association between socioeconomic position (SEP) and health related outcomes (Antonovsky, 1967; Krieger et al., 1997; Miranda et al., 2008; Bartley, 2004), also referred as the socioeconomic gradient in health, constitutes one of the most consistent findings of epidemiologic research. Individuals with a lower socioeconomic position, as measured by occupational position, educational attainment, income, or composite indexes, are more likely to die earlier and have a higher incidence of cardiovascular events, diabetes, obesity, and other diseases than their more advantaged counterparts (Bartley, 2004; Adler et al., 1993). As eliminating socioeconomic disadvantage from society is difficult, quantifying modifiable intermediate factors and targeting them could have important public health benefits. Epidemiologic research has long investigated potential mediating factors of the association between socioeconomic position and health outcomes, with health behaviors, environmental exposures or psychosocial factors having been identified as major mechanisms in the link between low SEP and increased disease risk (Supplementary Fig. 1) (Matthews et al., 2010; Stringhini et al., 2011a; Stringhini et al., 2012a; Robertson et al., 2015a; Næss et al., 2007; van Oort et al., 2005).

Health behaviors such as smoking, alcohol consumption, diet and physical activity (PA) are major risk or protective factors for chronic diseases (Who and Consultation, 2003; Centers for Disease C, Prevention, 2008; Klatsky et al., 1992) and are also strongly socially patterned, with detrimental behaviors being more prevalent in lower SEP groups when compared to higher SEP groups (Nocon et al., 2007; Macintyre, 2000; Wardle and Steptoe, 2003). Yet, despite extensive investigations, a clear understanding of the role of health behaviors in social inequalities in health is still lacking, a major challenge being that their estimated contribution to the socioeconomic gradient in health varies greatly across studies, ranging from 12% to 72% (van Oort et al., 2005; Stringhini et al., 2011b; Laaksonen et al., 2008; Lantz et al., 1998; Schrijvers et al., 1999; Skalická et al., 2009; Stringhini et al., 2010).

The reasons for the differential contribution of health behaviors to social inequalities in health are numerous and include cultural differences between countries (Stringhini et al., 2011b), demographic characteristics of the participants included in the studies (Tseng and Lin, 2008), between-studies differences in the SEP measures, health behaviors and health outcomes examined, and methodological differences in the calculation of the contribution of health behaviors (Stringhini et al., 2010; Bartley, 2016). Another potential explanation may be related to the stage of the epidemiologic transition, which designates the changes in the prevalence of diseases, disease risk factors, and the changes in the adherence to health behaviors over time and in different sociodemographic contexts (Mackenbach et al., 1997). However, there is currently no attempt in the literature to synthesize the wealth of research on this topic and provide a more comprehensive assessment of health behaviors as mechanisms underlying the association between SEP and health. However, this is a crucial step for identifying targets for policies aimed at reducing socioeconomic differences in health as well as improving health at the population level.

In this study, we conducted a systematic review and synthesis of the literature on the contribution of smoking, alcohol intake, physical activity and dietary patterns to socioeconomic inequalities in all-cause mortality and risk of cardiometabolic disorders, two health outcomes showing a particularly consistent socioeconomic gradient across studies (Avendano et al., 2006a; Suadicani et al., 2001; Stringhini et al., 2013a; Mackenbach et al., 2008). The overarching purpose of this review was to examine all previously published studies investigating the contribution of health behaviors to socioeconomic inequalities in health, and to provide a complete and comprehensive analysis regarding the sources of heterogeneity of this contribution, with a particular focus on methodological, sociodemographic and cultural factors.