Background Multimorbidity - the co-occurrence of multiple chronic conditions within the same individual – is a major global public health challenge.
People living in areas of greater deprivation have a higher burden of multimorbidity. It is not clear whether there are associations between other contextual (household and area-level) social determinants of health (SDoH), and multimorbidity. This study aims to systematically review the literature on associations between contextual SDoH and multimorbidity prevalence or incidence in the general population.
Methods A predefined search strategy (PROSPERO CRD42019135281) was run in 6 databases (MedLine, EMBASE, PsychINFO, Web of Science, CINAHL Plus and Scopus) in 2019. We included peer-reviewed studies published in English between 2010 and 2019, among general populations from high-income countries. We excluded studies if the SDoH did not align with the WHO’s SDoH framework and studies conducted solely with institutionalised individuals or young people (<18 years). A second reviewer independently screened all titles, abstracts and a subset of full-texts. Study quality was assessed using pre-specified criteria, and findings narratively synthesised.
Results From 3,298 records identified, 88 articles were reviewed on full-text and 41 papers met inclusion criteria (26 cross-sectional and 15 longitudinal). These spanned North America, Europe and Australasia. There was heterogeneity in definitions of multimorbidity; 34/41 studies defined multimorbidity as 2+ chronic conditions, whilst 8 used a cut-off point of 3+ (and some operationalised both). 35/41 studies included physical and mental health conditions, 4 only physical conditions and 2 failed to include this information.
Household SDoH studies most commonly investigated associations with household income, with few on tenure, composition and other circumstances. Studies with area SDoH most commonly investigated measures of socioeconomic deprivation with fewer investigating rurality.
Studies consistently reported that individuals with the lowest household incomes and living in the most deprived areas had the highest prevalence or incidence of multimorbidity. For example, crude multimorbidity prevalence in the most and least deprived areas was 69.9% and 60.2% in one study reporting the highest figures, and 12.3% and 10.3% in another reporting the lowest. These associations varied according to the definition of multimorbidity. Amongst the few studies that investigated tenure, composition and rurality, findings were inconsistent. Possible reasons for mixed findings include data and methodological limitations.
Conclusion Current understanding of household SD of multimorbidity is limited. Application of a consistent definition of multimorbidity is needed for quantitative synthesis of findings. Better understanding of the social factors driving multimorbidity is needed to develop equitable services and effective prevention strategies.
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