Conventional indirect indicators of iron status, using serum and red blood cell biomarkers, are confounded by inflammation from common infections in sub-Saharan Africa, a region with a high prevalence of iron deficiency, making the assessment of iron balance and efficiency of iron intervention difficult. A new method allowing accurate measurement of long-term oral iron absorption and allowing the estimation of iron requirements is highly needed. Such a novel method to quantify iron absorption and requirements using isotope dilution measurements in children should be validated in the present prospective observational study by following-up a group of 49 children given a stable iron isotope in an earlier trial. We will request seven blood samples within 2 years (sampling every four months) from the participants which will allow us to measure isotopic dilution for estimating total oral iron absorption over these 24 months.

Inclusion Criteria:

• Have participated in the original absorption study and the two follow-up samplings
• Signed written informed consent from the guardian to participate in the study

Exclusion Criteria:

• Long-term medication
• Any severe metabolic, gastrointestinal kidney or chronic disease such as diabetes, hepatitis, hypertension, cancer or cardiovascular diseases (according to the guardian's statement or med-ical examination (health booklet))
• Blood losses (surgery, accident) or blood transfusion during the past 4 months before study start.
• Residence too far away (> 2 hours by motorbike) from study location (Zomba)

Malawian children who ingested stable iron isotopes in the frame of a former iron absorption study.