OBJECTIVES: Fortification of breast milk (BM) is recommended to enhance protein, vitamin, and mineral content, supporting improved growth in preterm infants. However, the impact of fortification on the oxidant-antioxidant balance in BM has not been previously studied. This study aims to evaluate the effects of fortification with a bovine milk-based fortifier on the total antioxidant capacity (TAC) and total oxidant status (TOS) in preterm BM. METHODS: In this prospective cohort study, transitional milk (TM) (6-10 days postpartum) and mature milk (MM) (>
15 days postpartum) samples were collected from mothers of preterm infants receiving fortified BM. TAC and TOS were measured in BM samples before and after fortification. The oxidative stress index (OSI), defined as the TOS-to-TAC ratio, was used to assess oxidative stress levels. RESULTS: Seventy-five BM samples from 59 preterm infants, with a mean gestational age of 31.4 ± 2.8 weeks, were analyzed. TAC levels were consistent between TM and MM of the preterm infants. TOS levels and OSI were lower in TM compared to MM (p = 0.019 and p = 0.033, respectively). Fortification led to increased TAC and TOS in both TM (p <
0.001 each) and MM (p <
0.001 each). The OSI was higher in fortified TM (p = 0.032) compared to unfortified TM, while OSI remained unchanged in fortified MM (p = 0.39). CONCLUSIONS: Preterm TM exhibits a more favorable oxidant-antioxidant profile compared to MM. Fortification elevates both TAC and TOS in preterm BM. In MM, the oxidant-antioxidant balance is maintained post-fortification
however, in TM, the increase in TOS exceeds that of TAC, resulting in a higher OSI.