This study compares weekly versus daily administration of iron for prevention of anemia in 6 months old infants. One third of the infants that are exclusively breast fed will not receive iron, the second third will receive iron weekly and the last third will receive iron daily. Half of the infants that take infant formula will receive iron weekly and the other half will receive iron daily.

Iron deficiency is the most prevalent nutritional deficiency and the main cause of anemia. It's estimated that 43% of pre-school children worldwide are anemic, in Argentina a national survey carried out in 2007 (last survey), showed that 34.5% of children less than 2 years old were anemic and that 50.8% of children 6 to 9 months old were anemic. Although there is a consensus on iron supplementation as a preventive strategy for anemia in infants, there is a poor adherence due mainly to mild gastrointestinal adverse effects and low prescription rates from pediatricians. On the other hand, the excess of iron can lead to genomic instability with structural and functional alterations on proteins, lipids and DNA. Weekly administration of iron has been proposed as an alternative of similar efficacy and higher effectiveness in older children and pregnant women, but sufficient evidence for infants is lacking.

Inclusion Criteria:

• 3 months old infants, clinically healthy, born to term (>37 weeks), that weighted at birth between 2500 and 4000 g, that have normal prenatal records.

Exclusion Criteria:

• anemic or iron deficient infants, or that have a chronic pathology, or that have undergone an acute pathology in the previous 15 days. Children that are receiving antibiotics or vitamin supplements.

Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices).

Beginning 3 months following article publication. No end date.

Researchers who provide a methodologically sound proposal.Proposals should be directed to enriqueflmartins@gmail.com To gain access, data requestors will need to sign a data access agreement.

Outcomes assessor: the outcomes are defined by hemoglobin and ferritin (corrected by CRP), also genomic instability is defined by a laboratory result such as comet assay. The members of the laboratory will receive labeled specimens with a code unrelated to the allocated arm.

The investigators that will analyze the data will not carry out the study. All the clinical data will be obtained by the care providers.