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Childhood socioeconomic status and inflammation: A systematic review and meta-analysis

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Highlights

  • A systematic review identified 35 studies (26 unadjusted; 31 adjusted effect sizes).

  • A meta-analysis showed an inverse relationship between SES and inflammation.

  • This association remained significant in after adjusting for several factors.

  • Effect became non-significant when only using studies controlling for adulthood SES.

Abstract

Recent research suggests that risk for chronic diseases of aging including cardiovascular disease, diabetes, and even cancer can be programmed early in the lifespan as a result of exposure to chronic stressors like low socioeconomic status (SES) that are hypothesized to promote a pro-inflammatory response in immune cells that results in chronic, systemic inflammation. The present paper conducted a meta-analysis to establish whether exposure to low (versus higher) SES in childhood and adolescence is associated with higher levels of inflammation (as measured by C-reactive protein, IL-6, and fibrinogen) concurrently and in adulthood. We conducted meta-analyses with both unadjusted bivariate associations between SES and inflammation and with adjusted associations that controlled for a range of covariates including demographic factors, body mass index, smoking, physical activity and current SES. A systematic review of Pubmed and PsycINFO identified a total 35 studies (26 with unadjusted and 31 adjusted effect sizes) to be included in the meta-analysis. Random-effects meta-analysis showed that individuals who were exposed to low SES in childhood and adolescence had significantly higher levels of inflammatory markers (r = −0.07, p < .001, 95% CI = −0.09, −0.05). This association remained significant in adjusted analyses (r = −0.06, p < .001, 95% CI = −0.09, −0.03). However, the relationship between childhood SES and inflammation was non-significant in a meta-analysis with longitudinal studies that all controlled for adulthood SES (r = −0.03, p = .356, 95% CI = −0.08, 0.03). Future longitudinal research should utilize measurement of inflammatory markers at multiple time points to further examine the complex relationships between SES and health both in childhood and adulthood.

Section snippets

Mechanisms of childhood SES effects on health

The pathogenic mechanisms that mediate the relationship between SES and disease are not fully understood, especially since lack of exercise, smoking, body mass index (BMI) and other factors that are also associated with SES do not completely account for these associations (Miller et al., 2011). In the past decade, researchers have become increasingly interested in the possibility that low-grade, chronic inflammation is the underlying mechanism linking risk factors like low childhood SES and

Empirical studies on childhood SES and inflammation

Research on the relationship between childhood SES and inflammation is equivocal. Some studies find no significant relation; others find a small but significant inverse relationship. In some studies, these associations persist after controlling for demographic and health factors, but in others, associations become non-significant after controlling for covariates. In addition to socio-demographic variables such as age, sex, and race, research has also shown that health related factors that are

Current study

We build on results from one systematic review (Nazmi and Victoria, 2007) and a recent meta-analysis (Liu et al., 2017). Nazmi and Victoria (2007) primarily reviewed studies of adult SES and CRP and found that most of these reported an inverse relationship. This review included few studies of childhood SES and CRP. A recent meta-analysis using 14 studies examining childhood SES and adult CRP found that participants from the least advantaged families had 25% higher CRP levels than participants

Search strategy and selection

A systematic review of the literature was performed using Pub Med and PsycINFO using the search criteria: “(socioeconomic OR SES) AND (inflammation OR inflammatory OR C-reactive OR CRP OR IL-6 OR IL-1 OR tumor necrosis factor OR tnf OR cytokines OR interleukin OR fibrinogen) AND (child* OR youth OR adolescen* OR early life)”. Search criteria were restricted to original peer-reviewed papers, in the English language, using human subjects. The literature search was performed between 4 March and 14

Systematic review

The initial search produced 998 papers in Pub Med and 166 in PsycINFO total. After screening and removal of duplicates (N = 28), 72 papers were chosen for in-text analysis including three additional studies that were included after an updated search. Following an in-text analysis, 37 were excluded (9 no childhood SES; 8 no inflammatory markers; 4 no individual SES; 5 an acute response; 2 a medical population; 7 duplicate cohorts; 2 no effect size available for either unadjusted or adjusted

Discussion

Our results showed a small but inverse relationship between childhood socioeconomic status and markers of chronic inflammation that remained significant across adjusted analyses, type of inflammatory markers, and type of SES measures utilized. In addition, for both unadjusted and adjusted analyses, the effect remained significant in both cross-sectional and longitudinal studies, even after only including studies that controlled for BMI. However, the effect between SES and inflammation was

Limitations

There are several caveats that should be considered in the interpretation of these results. Studies of SES and inflammation employ a range of statistical methodologies that produce many types of effect sizes (odds ratios, path coefficients from structural equation models, relative risk ratios, standardized and unstandardized regression coefficients, means, etc). For this meta-analysis, only a handful of studies used similar statistical techniques and effect sizes. Although the unadjusted

Conclusion

The present meta-analysis found a small but significant inverse association between childhood SES and chronic inflammation that remained significant across different inflammatory markers, SES measures, study designs, and after controlling for BMI. Results showed that the concurrent effect of childhood SES on childhood inflammation could be consistently and reliably detected in cross-sectional data suggesting immediate versus more long-term effects on inflammatory mechanisms. However, the

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