Socioeconomic status in childhood and C reactive protein in adulthood: a systematic review and meta-analysis

Abstract

Background: Inflammation plays a central role in cardiometabolic disease and may represent a mechanism linking low socioeconomic status (SES) in early life and adverse cardiometabolic health outcomes in later life. Accumulating evidence suggests an association between childhood SES and adult inflammation, but findings have been inconsistent.

Methods: We conducted a systematic review and meta-analysis of observational studies to quantify the association between childhood (age <18 years) SES and the inflammatory marker C reactive protein (CRP) in adulthood. Studies were identified in Medline and Embase databases, and by reviewing the bibliographies of articles published from 1946 to December 2015. Study-specific estimates were combined into meta-analyses using random-effects models.

Results: 15 of 21 eligible studies (n=43 629) were ultimately included in two separate meta-analyses. Compared with those from the most advantaged families, participants from the least advantaged families had 25% higher CRP levels (ratio change in geometric mean CRP: 1.25; 95% CI 1.19 to 1.32) in minimally adjusted analyses. This finding was attenuated by the inclusion of adult body mass index (BMI) in adjusted models, suggesting BMI has a strong mediating role in CRP levels.

Conclusions: We observed an inverse association between childhood SES and adulthood CRP, potentially mediated through BMI. Investigating how childhood SES is associated with childhood BMI and CRP would provide insight into the effective timing of social and clinical interventions to prevent cardiometabolic disease.

Keywords: Cardiovascular disease; OBESITY; SOCIAL INEQUALITIES; Social and life-course epidemiology.

Figure 1. Directed Acyclic Graph Outlining Potential Mechanisms Through Which Childhood SES Determines Adult C-Reactive Protein

Mechanisms broadly categorised into 2 life-course models, the critical period model (A) and the chain of risk models (B) [17]. Model A1 (direct effect of childhood SES on adult CRP) posits a critical window early in life where later life CRP is determined. Model B1 (indirect effect via adult SES), Model B2 (indirect effect via childhood BMI, and adult SES), Model B3 (indirect effect via childhood BMI to adult SES to adult BMI) and Model B4 (indirect effect via BMI in childhood and adulthood) posit that a chain of risk factors accumulate throughout life to increase CRP levels in adulthood. SES, socioeconomic status; BMI, body mass index; CRP, C-reactive protein.

Figure 2. Flowchart Detailing Numbers of Studies Screened, Assessed and Included in the Review, with Reasons for Exclusions

Figure 3. Unadjusted or Minimally Adjusted Results from Stratified Meta-Analysis of the Association Between Childhood Socioeconomic Circumstance and Adult Geometric Mean CRP Levels (Random-Effects Model), according to study design

Relative change in CRP comparing the lowest SES category with the highest SES category, according to either parental, maternal or paternal occupational rank, education level or childhood adversity. Solid diamonds represent study-specific point estimates; squares represent study-specific weights in stratified and final meta-analyses; horizontal bars represent 95% confidence intervals, and hollow diamonds represent summary estimates, with the width of the diamond corresponding to the 95% confidence interval of the summary. Income-based estimates were excluded if occupation-based estimates were available from the same study, and occupation estimates excluded if education estimates available, to avoid over weighting papers that conducted multiple analyses on the same population. Meta-analysis stratified according to study design and whether parental SES data was collected longitudinally or retrospectively. CRP, C-reactive protein; SES, socioeconomic status.