Sex Differences in Early Childhood Growth in a Resource-Limited Setting: A Secondary Analysis of the Early Life Interventions in Childhood Growth and Development in Tanzania (ELICIT) Study.

Background: In population-based growth surveys in sub-Saharan Africa, boys have higher rates of growth failure than girls.

Objectives: Our goal was to assess for the presence, timing, and potential etiology of sex-based differences in length-for-age z score (LAZ), weight-for-age z score (WAZ), and head circumference-for-age z score (HCZ) in a birth cohort in rural Tanzania.

Methods: We performed a secondary analysis of randomized controlled trial data on 1084 children followed from age <2 wk to 18 mo, assessing anthropometry (measured every 3 mo), illness (hospitalization and monthly maternal report of symptoms), and feeding [monthly maternal report of exclusive breastfeeding (EBF) and complementary solids and liquids (CSLs)]. We used linear regression to assess sex differences in LAZ, WAZ, and HCZ over time.

Results: Although male and female infants had similar anthropometry measures at study entry, males exhibited poorer growth through 6 mo (e.g., 3-mo mean LAZ: males -0.94, females -0.74, P < 0.01; 3-mo mean WAZ: males -0.63, females -0.48, P < 0.05), without significant worsening from 6 to 18 mo. Males had lower HCZ only at 9 mo. In evaluating possible etiologies, mediation analysis failed to identify illness or hospitalization as mediators of poorer growth among males, although at age 3 mo, males with recently reported illness exhibited greater decline in WAZ than females with illness (ΔWAZ: males -0.24, females 0.03, heterogeneity test P = 0.01). Differences in EBF and introduction of CSL did not explain the sex-based growth outcomes.

Conclusions: In longitudinal analysis, males exhibited more severe growth failure by 3 mo than girls and did not exhibit catchup growth between 6 and 18 mo. Reported symptoms of illness and early introduction of CSL did not appear to be mediators of these sex-based differences, although likely not all sickness was captured by monthly maternal report. Given the early nature of these deficits, LAZ and WAZ measures at 6 mo may be good outcomes for intervention studies targeting improvements in early childhood growth and thriving.