Girl child marriage, socioeconomic status, and undernutrition: evidence from 35 countries in Sub-Saharan Africa

BACKGROUND: Girl child marriage, a formal union of a female before age 18, and undernutrition remain common in Sub-Saharan Africa. The aim of this study is to establish the extent to which girl child marriage contributes to socioeconomic status and underweight, a measure of undernutrition, among adult women. METHODS: We used data from 103 Demographic and Health Surveys (DHS), representing 35 African countries from 1991 to 2014. Girl child marriage was coded both as a binary variable (before 18 years) and categorical variable (before 14, 14 to 15 years, 16 to 17 years). The primary outcome was underweight (body mass index less than 18·5). Secondary outcomes were early and multiple childbearing, secondary education completion, and wealth index. Logistic regression models were used to estimate associations. RESULTS: Fifty-five percent of women married before age 18. Girl child marriage was associated with reduced risk of being underweight both in models adjusted for basic confounders (risk difference = − 0.020, 95% CI [− 0.026, − 0.014], p < 0.01) and in models adjusted for childbearing, women’s relative status, and socioeconomic outcomes (risk difference = − 0.018, 95% CI [− 0.024, − 0.011], p < 0.01). Conditional on completing primary education and community fixed-effects, women married before 18 years had an increased risk of early motherhood (risk difference = 0.38, 95% CI [0.38, 0.38], p < 0.01) and of being in the poorest quintile (risk difference = 0.024, 95% CI [0.012, 0.036], p < 0.01), and were 27 percentage points less likely to complete secondary education (risk difference = − 0.27, 95% CI [− 0.28, − 0.26)], p < 001), compared to women married as adults. CONCLUSIONS: Though associated with substantially reduced socioeconomic status, girl child marriage appears to be associated with slightly reduced risk of being underweight in the population studied. Further research is needed to understand the determinants of undernutrition in this context as well as the broader relationship between socioeconomic status and nutritional outcomes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12916-019-1279-8) contains supplementary material, which is available to authorized users.