This is a study to evaluate the effects of vitamin A supplementation program on the vitamin A status of preschool children. All children aged 3-5 years who do not have severe illness and are not planning to move from the study area are eligible. Children whose caregivers agree to sign the consent form will be enrolled in their community and submitted to a longitudinal evaluation of vitamin A status before and after vitamin A supplementation campaign.

Vitamin A status will be assessed by measuring serum retinol, retinol binding protein and vitamin A total body pool size using stable isotope dilution methodology.

Five months after the last supplementation (day 0), an oral dose (2 mg retinol equivalents) of label vitamin A ([2H8]-retinyl acetate) in oil will be administered to 80 eligible children together with a low vitamin A high-fat snack. Fasting venous blood samples (about 7 ml) will be collected into evacuated foil-wrapped blood collection tubes specifically designed for the collection of serum (containing no anticoagulant and metal free) on the mornings of days 0 before the administration of the dose and on day 14 for quantitative estimation of initial vitamin A pool size and determination of potential confounding parameters (CRP, AGP, iron, zinc, malaria, carotenoids and retinoids). About six months after the last supplementation (day 30), each child will received the vitamin A supplement. After 30 days and 90 days, two groups of 40 children (Grp1, Grp2) will respectively received a second dose of labeled vitamin A ([2H4]-retinyl acetate); fasting venous blood samples will be obtained before the administration of the dose and 14 days after dosing for quantitative estimation of final vitamin A pool size and determination of potential confounding parameters.

Inclusion Criteria:

• Children will be included if they are in the target age range (36-59 months), are not planning to move from the study area for the duration of the study and do not have severe illness at the time of enrolment

Exclusion Criteria:

• Exclusion criteria will generally include the following conditions: severe anaemia, severe acute malnutrition, obesity, or clinically defined severe illness, such as dehydration, severe diarrhoea, malaria or severe respiratory illness