Trends in prevalence and predictors of anemia among school-aged children in Tanzania: analysis of 2019–2023 cross-sectional surveys using a multilevel logistic regression model

BACKGROUND: Anemia constitutes a major global public health challenge among school-aged children with documented impacts on psychomotor development, academic achievement, susceptibility to infections, and long-term economic productivity. This study presents nationally representative findings on the prevalence and determinants of anemia among school children aged 5-16 years in mainland Tanzania. METHODS: Data were collected as part of the cross-sectional Tanzania School Malaria Parasitological Survey (SMPS) in 2019, 2021, and 2023. Hemoglobin concentration was assessed using the HemoCue Hb 201 + analyzer, and anemia status was classified according to the 2024 WHO thresholds. Candidate predictors associated with anemia (p < 0.2 in univariable analyses) were included in a multivariable multilevel logistic regression model to assess the contribution of predictor variables to anemia prevalence and to calculate adjusted odds ratios (AOR) and 95% confidence intervals (CI). RESULTS: The study surveyed 47,366 school-aged children from 810 schools across three survey rounds. Generally, anemia prevalence was 45.5% (mild: 18.5%, moderate: 25.4%, severe: 1.5%). On multivariable regression of anemia risk, a statistically significant interaction was observed between age and sex. While odds of anemia were similar between sexes in lower age groups (5-11 and 12-14 years), male children aged 15-16 years old had almost three times the odds of anemia compared to female children in the same age group (AOR 2.96 [95%CI 2.18-4.02]). Malaria infection significantly increased anemia odds (AOR 1.88 [95%CI 1.75-2.01]). Regional disparities were noted, with the Lake [AOR 1.77 (95%CI 1.38-2.26)] and Western [AOR 1.78 (95%CI 1.34-2.37)] zones having highest odds of anemia compared to the Central zone. Over time, anemia risk decreased, with a notable reduction in 2023 (AOR 0.75 [95%CI 0.70-0.80]) compared to reference year (2019). CONCLUSIONS: Anemia in school-aged children remains a severe public health problem in Tanzania, according to WHO classifications. Risk factors include older age, male sex, malaria infection, and living in moderate and high malaria transmission risk areas and zones like the Lake, West, and Southern. These findings highlight the need for collaborative efforts by stakeholders to address anemia not only in Tanzania but also in regions with similar challenges.