Human milk and antioxidative protection

Human milk (HM) is considered the ideal food for healthy infants129 and is known to contain various bioactive substances, some of which are reported to be anti-oxidants.130 HM contains many antioxidants such as enzymes (CAT, GPx, SOD), vitamins (A, C, E), binding proteins such as lactoferrin, and constituents of antioxidative enzymes (Cu, Zn).131-133 In contrast, antioxidative enzymes are absent from infant formula.134 Most infant formula has higher amounts of vitamins added than are present in HM to make up for the reduced bioavailability. Thus, the overall antioxidant capacity of HM versus infant formula is difficult to assess, although assessment would probably favor HM.14

We previously reported in vitro results showing that HM alleviated H2O2-induced oxidative damage in intestinal epithelial cell lines, whereas bovine milk or infant formula did not.135 Confluent intestinal epithelial (IEC-6) cells were preincubated with defatted HM, bovine milk, or three artificial milks for 24 hr followed by H2O2 challenge. HM-treated cells showed the highest survival rates (50%) compared with bovine milk-treated (6%) or infant formula-treated (13 to 16%) cells (Figure 5.6).135 Buescher and Mcllherhan131 reported that human colostrum manifested antioxidant properties, proving capable of spontaneous reduction of cytochrome C, depletion of polymorphonuclear leukocyte-produced H2O2, and protection of epithelial cells from polymorphonuclear leukocyte-mediated detachment.

Several clinical studies demonstrated antioxidative properties of HM. HM-fed infants had higher plasma trapping ability (a measure of resistance to oxidative stress in vitro) than did control infants fed formula.136 We compared the oxidative stress levels in 41 healthy 1-month-old infants and 29 premature infants by measuring urinary 8-hydroxy-2-deoxyguanosine (8-OHdG — a marker of oxidative DNA damage). In the 1-month-old group, urinary 8-OHdG excretions of the breast-fed infants were significantly lower than those of the artificial formula-fed infants (Figure 5.7).137 In the premature group, urinary 8-OHdG excretions of the breast-fed infants at 14 and 28 days of age were significantly lower than those of the formula-fed infants (Figure 5.8).138 These data indicate that HM provides more antioxidant properties than infant formula during early infancy. This may be due to the presence of antioxidants in HM that may exhibit antioxidant effects in the gut and may pass through the relatively porous neonatal intestine early in infancy.131,132 In fact, feeding with HM has been associated with a lower incidence of a variety of illnesses including NEC,139 respiratory disease,140 and ROP141 in premature infants.

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