Economic inequality in malnutrition: a global systematic review and meta-analysis

Objective To describe the evidence on global and regional economic inequality in malnutrition, and the associations between economic inequality and malnutrition. Methods We conducted a systematic review and meta-analysis. Between Nov 1 2020 and Jan 22 2021, we searched Medline, Embase, Global Health, Eldis, Web of Science, and EBSCO Discovery Service. We contacted 39 experts and tracked citations. We included any study reporting a concentration index (CIX) relating economic status and nutritional status, or any multi-level study reporting an association between economic inequality and nutritional status. Nutritional status was measured as stunting, wasting, anaemia, or overweight in children (<5 years), or underweight, overweight or obesity, or anaemia in adults (15-49 years). We had no study date or language restriction. Quality was assessed using the Appraisal Tool for Cross-Sectional Studies (AXIS tool). We mapped estimates and pooled them using multi-level random-effects meta-analyses. Results From 6185 results, 91 studies provided 426 CIX (>2.9 million people) and 47 associations (3.9 million people). Stunting (CIX -0.15 [95% CI -0.19 to -0.11]) and wasting (-0.03 [-0.05 to -0.02]) are concentrated among poor households. Adult overweight and obesity is concentrated in wealthier households (0.08 [-0.00 to 0.17]), particularly in South Asia (0.26 [0.19 to 0.34]), but not in Europe and Central Asia (-0.02 [-0.08 to 0.05]) or North America (-0.04 [-0.10 to 0.03]). We found no association between 0.1 increase in Gini coefficient and adult underweight (odds ratio 1.03 [95% CI 0.94 to 1.12]) or overweight and obesity (0.92 [0.80 to 1.05]). Conclusions There is good evidence that the prevalence of malnutrition varies by levels of absolute economic status. Undernutrition is concentrated in poor households, whereas concentration of overweight and obesity by economic status depends on region, and we lack information on economic inequalities in anaemia and child overweight. In contrast, links between malnutrition and relative economic status are less clear and should not be assumed; robust evidence on causal pathways is needed.