Irisin concentration in infant formulas and breast milk.

Background: Irisin is a newly discovered myokine with antiobesity properties. The delivery of irisin with the breast milk or formula is an emerging concept that myokine present at human milk influences postnatal energy balance and developmental parameters. The aim of the study was to evaluate irisin concentration in breast milk of mothers with term and preterm babies and in infant formulas.

Methods: A total of 49 lactating mothers were enrolled in the study: 31 mothers of very low birth weight preterm infants and 18 mothers of term infants. Milk samples were collected twice: during the first week after delivery and after 4 weeks of delivery. Irisin concentration was determined using ELISA kits both in human milk and in samples of 14 different infant formulas.

Results: There were no differences in milk irisin levels between preterm and full-term milk samples during both the 1 and the 4 week after delivery. There were also no differences in irisin concentration between transitional milk and mature milk in both tested groups. Irisin concentrations in preterm and full-term milk were significantly higher than in formulas for 30 days period after delivery. A significant increase of irisin concentration in natural milk 4 weeks postdelivery in comparison to 1 week after delivery was observed (mean difference 0.362 µg/mL; P=0.0063).

Conclusions: This study provides evidence that irisin is present in infant formulas, although in less amount than in human milk. Further research is needed to assess, if children fed with infant formulas may disadvantage from lower irisin supply.