Review ArticleThe contribution of health behaviors to socioeconomic inequalities in health: A systematic review
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.
Section snippets
Search strategy and inclusion criteria
In this systematic review, we aimed to retrieve and analyze all articles that examined the contribution of health behaviors to the socioeconomic gradient in all-cause mortality and cardiometabolic disorders. We used four main groups of search terms: terms related to SEP, terms related to health behaviors, terms related to health outcomes, and terms related to “contribution”, “role”, or “mediation” (Supplementary Material – search strategy). Article search was performed from August 2015 to
Results
Our search strategy identified 855 potentially relevant articles, of which 740 were found in three electronic databases and 115 were retrieved from reference lists. The article selection process and flow-chart are presented in Supplementary Fig. 2. A total of 537 articles were rejected based on Title/Abstract screening. These studies were mostly health intervention programs, randomized controlled trials or other experimental studies, did not assess the association between SEP and a health
Discussion
In this study, we reviewed the evidence on the contribution of smoking, alcohol consumption, physical activity and dietary patterns on social inequalities in all-cause mortality and cardiometabolic disorders. We confirmed the existence of a strong association between SEP and health outcomes, and showed that health behaviors contribute to the SEP gradient in health to varying degrees. In general, the contribution of health behaviors to socioeconomic differences in health was higher in studies
Conclusion
This is the first study to provide a complete and comprehensive synthesis on the factors influencing the contribution of health behaviors to the socioeconomic gradient in health. We observed that health behaviors overall contribute to the association between SEP and health outcomes, but that this contribution varies substantially according to geographic location, sex, age, health outcomes and methodological differences between included studies, the main reason for this heterogeneity being the
Compliance with ethical standards
For this type of study ethics approval is not required.
Conflicts of interest
None.
Acknowledgments
The authors would like to express their gratitude to Professor Katherine Frohlich (University of Montreal) and Professor Mauricio Avendano Pabon (University of Harvard) for helping improve this manuscript. The authors would also like to thank all the collaborators of the Lifepath project (http://www.lifepathproject.eu/).
Funding
This work is supported by the Lifepath project, which is funded by the European commission and the Swiss State Secretariat for Education, Research and Innovation - SERI (Horizon 2020 grant n° 633666). Silvia Stringhini is supported by the Swiss National Science Foundation (Ambizione Grant n° PZ00P3_167732). The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of data; and preparation, review or approval of the
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