Letters to the Editor

Breastfeeding and iron status

Iron deficiency in infants fully breastfed for 6 months may not be transitory: first observations during the second half of infancy

Madam

The advisable duration of exclusive breastfeeding has been a matter of debate in the field of public health nutrition in recent years. Before 2001, the WHO recommended that infants should be exclusively breastfed for 4–6 months. In 2001, after a systemic review and expert meeting, this advice was changed to recommending exclusive breastfeeding for the first 6 months of life as public health measure⁽¹⁾. At the same time it was recognized that exclusive breastfeeding up to 6 months may impose a risk of marginal Fe status in susceptible infants⁽²⁾. This is one of the reasons why the latest comment by the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition recommends the introduction of complementary food (CF) between 4 and 6 months (17 and 26 weeks) of age⁽³⁾.

Very recently, Yang et al.⁽⁴⁾ published a valuable report assessing the prevalence of iron deficiency (ID; ferritin <12 μg/l) and iron-deficiency anaemia (IDA; ferritin <12 μg/l and Hb <105 g/l) among fully breastfed infants with a birth weight >2500 g before 6 months of age. They were able to summarize data from their own six randomized clinical trials conducted in four countries worldwide. They found a percentage of infants with IDA before 6 months of <10 % in these six studies. They discuss that IDA in these fully breastfed infants may be transitory, if Fe-rich or Fe-fortified CF are consumed beginning at 6 months. However, they acknowledge that evidence on this question is lacking.

Regarding this question, we re-evaluated data from the Dortmund Intervention Trial for Optimization of Infant Nutrition (DINO). DINO is a double-blinded, randomized, controlled intervention trial that compared primarily the effect of different amounts of meat in CF on the Fe status of infants in the second half of infancy⁽⁵⁾. In addition, fatty acid status was examined⁽⁶⁾. The study cohort was fed according to German and European dietary guidelines including introduction of CF between 4 and 6 months.

Term-born, healthy infants were randomized into a ‘high meat’ group (HM, n 48) receiving commercial baby jars with a meat content of 12 % by weight (according to paediatric guidelines) and a ‘low meat’ group (LM, n 49) receiving meals as marketed (meat 8 % by weight, the lowest level of EU law). Intervention was from 4 to 10 months of age. Dietary intake was recorded continuously; repeated venous blood samples were collected.

In the primary analysis of the total sample including breastfed and (Fe-fortified) formula-fed infants, Fe status was adequate before (4 months), during (7 months) and after (10 months) the intervention. In a secondary analysis in the subgroup of infants who were fully breastfed for 4–6 months (those infants with the lowest dietary Fe intake during the first half of infancy), there was weak evidence of an increased risk to develop ID and IDA during the second half of infancy⁽⁵⁾.

Actually, using the definitions of Yang et al.⁽⁴⁾, we found that eleven out of fifty-three infants fully breastfed for 4–6 months presented with ferritin <12 μg/l, indicating ID, at 10 months of age. One of these showed Hb <105 g/l, indicating development of IDA. On the other hand, none of those infants on Fe-fortified formula during the first 4 months presented with low values of ferritin or with Hb <105 g/l at the age of 10 months.

These findings of the DINO study, representing a population from a developed country, indicate that the potential risk for the development of Fe deficiency in infants fully breastfed in the first 6 months may not be transitory even when CF with highly bioavailable Fe (from meat) is consumed. Our findings are consistent with a recent re-evaluation⁽⁷⁾ of current recommendations for the optimal duration of exclusive breastfeeding. The authors concluded that, although there is a persuasive scientific evidence for exclusive breastfeeding for 6 months rather than 4–6 months for infants in developing countries, this evidence is weaker for infants in developed countries.

In conclusion, the results of this re-evaluation of the DINO study analysis show low values of ferritin and of Hb at 10 months of age in some infants fully breastfed for the first 4–6 months and support the recommendation of an age range of 4–6 months for introduction of Fe-rich CF in infants in developed countries. However, further trials specifically designed to investigate the risk of Fe deficiency during the second half of infancy in healthy infants fully breastfed for the first 4–6 months of age are necessary.

We completely agree that knowledge on the development of Fe metabolism during infancy is still limited in spite of growing awareness that nutrition during infancy may have profound biological effects and important consequences for both short- and long-term health. This is especially true considering the regulation of Fe metabolism in healthy, fully breastfed infants during the period of complementary feeding^{(3, 7)}.