The Impact of Age on Income-Related Health Status Inequalities from Birth to Adolescence: A Systematic Review with Cross-Country Comparisons

Objectives: To examine the effect of age on associations between household income and overall health from birth to adolescence, and whether age patterns vary by country. It is uncertain whether income-related health inequalities remain stable, widen, or narrow as children age, which impacts optimal timing of equity-focused interventions. Study design: Systematic review (CRD42016038583) of MEDLINE, Embase, PsycINFO, CINAHL, SocINDEX (full-text), and EconLit (full-text) to April 2017. We included observational studies and trials in children and adolescents (0-18 years of age), examining age differences in associations between income and overall health (self-rated, clinician-rated, proxy-rated). One reviewer extracted data; 2 evaluated risk of bias. Results: Thirty-eight articles containing 43 studies (30 cross-sectional, 13 cohort) were identified, from high-income (n = 39) and middle-income (n = 4) countries. In the US (n = 21), positive income-health associations emerged in early childhood, and these inequalities typically widened progressively into adolescence. Relative to 0- to 3-year-olds, ratios of income-health coefficients ranged from 1.10-3.71 for 4-8 years of age, 1.26-3.86 for 9-12 years of age, 1.36-6.71 for 13-17 years. In the United Kingdom and Ireland (n = 8), inequalities emerged in early-to-mid childhood, but age patterns were less consistent. In other high-income countries (Australia, Canada, France, Germany, Japan, Republic of Korea), inequalities mostly persisted or widened with age. In middle-income countries, inequalities appeared to narrow (Indonesia n = 2) or persist (Brazil n = 2) with age. Limitations are unclear/high risk of bias and dataset overlap for some studies. Conclusions: In many countries, income-related health status inequalities persist or widen as children age. Interventions that improve health equity early in the life-course are needed.