Adequate levels of vitamin B12 (cobalamin) is necessary for normal growth and development in infants. We have earlier investigated cobalamin status in healthy children and we observed metabolic evidence of impaired cobalamin status during the first 6 months, but not later in life.

The purpose of this study is to determine if cobalamin supplementation may influence the metabolic profile related to cobalamin status in infants.

During fetal life and infancy, an adequate cobalamin status is important for normal growth and central nervous system development. A metabolic profile consistent with impaired cobalamin status is prevalent in breast-fed infants. Whether this profile reflects immature organ systems or cobalamin deficiency has not been clarified.

Low levels of cobalamin, elevated levels of total homocysteine (tHcy), cystathionine and/or methylmalonic acid (MMA) in the blood are measures of impaired cobalamin status.

The purpose of this randomized, controlled study is to determine if cobalamin supplementation may influence the metabolic profile related to cobalamin status in infants.

Six weeks old infants will be randomly assigned to receive either an intramuscular injection with 400 µg cobalamin or no intervention. Concentrations of cobalamin and folate in serum, and total homocysteine (tHcy), methylmalonic acid (MMA) and cystathionine in plasma will be determined at inclusion and at the age of 4 months. A questionnaire on infant and maternal nutrition, vitamin supplementation, growth parameters, parity and maternal use of tobacco will be completed.

Inclusion Criteria:

• 6 weeks old infants
• The infant should be healthy and not have any serious malformations
• The mother should be healthy and not have any serious disorders or use any daily medications
• The mother should have an ordinary omnivorous diet

Exclusion Criteria:

• If there are evidence of serious infant disease during the study period, the infant should be excluded from the study