Determinants of vitamin a deficiency in children between 6 months and 2 years of age in Guinea-Bissau

Randomized, placebo-controlled trial of vitamin A supplementation; participants: children aged 6 months to 2 years in rural Guinea-Bissau who missed at least one routine vaccination and had not received vitamin A within the previous month; enrollment Aug 2007–Nov 2010; baseline vitamin A status and infection assessed via dried blood spots measuring retinol-binding protein (RBP) and C-reactive protein (CRP); 1254 samples collected; 1102 included in VAD analyses; large model included 1050 due to missing information.

VAD prevalence was 65.7% overall (95% CI 62.9–68.5); 60.2% after excluding infected children; using alternative DBS cut-offs yielded 57.5% (lower) and 73.5% (higher). Rainy season increased VAD risk (PR 1.64; 95% CI 1.49–1.81). Ethnicity and region showed strong variation; Bijagós/Bolama, Gabu, Tombali had >2-fold higher risk vs Biombo. Having a live vaccine as most recent vaccination reduced VAD risk (PR 0.84; 95% CI 0.74–0.96). Infection (CRP >5 mg/L) increased risk (PR 1.27); twins higher risk (PR 1.30); cough at inclusion day associated with higher risk (PR 1.10). Sex and age had weaker effects; timely vaccination (9–11 months) did not confer clear protection. Overall, VAD remains a major public health problem with seasonal and geographic variation; vitamin A supplementation during the trial did not show a consistent beneficial impact on vitamin A status, suggesting alternatives such as fortification, vitamin A–rich foods, or more frequent low-dose supplementation.

Potential overestimation of VAD due to incomplete correction for infection (α1-acid-glycoprotein not included); sample restricted to children missing vaccines (may not reflect the general population); regional sampling not perfectly proportional to population sizes; DBS-based RBP measurement and cut-offs may misclassify VAD; missing data reduced sample size for the large model; possible residual confounding; cross-sectional baseline assessment within a trial context.