Total Antioxidant Capacity in Breast Milk 135 Fig. 1. Total antioxidant capacity in correlation with day after delivery (n = 6) and formula milk B (n = 6), which were 2739 ± 126.1 µ mol/L and 2602 ± 152.4 µ mol/L, respectively. The average TAC in formula milk (formula milk A and formula milk B) was 2671 ± 96.0 µ mol/L and the TAC (n = 56) in breast milk was 3807 ± 103.5 µ mol/L, clearly revealing that TAC in breast milk is higher than TAC in formula milk (p<0.0001). Fig. 1 shows the correlation between TAC and the postnatal age in days when the breast milk was collected. The TAC in breast milk was negatively correlated to the postnatal age in days when collected (r2 = 0.25, p<0.0001), while significantly higher than the average TAC in formula milk. Discussion Despite the fact that formula milk, which is made to simulate breast milk, has the same level of exogenous antioxidants as breast milk (Table 1), the TAC of breast milk is higher than that of formula milk. Moreover, although the TAC in breast milk was observed to decrease with the passage of time after birth, TAC in breast milk throughout the period of this study (postnatal days 4–145) was continually higher than the average TAC in formula milk. These are highly interesting results (Fig. 1). A conceivable reason for these results is the action of endogenous anti- oxidants, such as superoxide desmutase (SOD), glutathione peroxidase (GP), and catalase (CAT), which are present only in breast milk and not in formula milk [24, 25]. There are only two or three reports that measure both the endogenous and exogenous TAC in breast milk [13, 14]. The values in the common measurement method, which uses 2,2-azino-di-3-ethylbenzthiazolinesulph onate (ABTS), have a range of less than 1, and so are statistically limited if there are only a few samples and could therefore be biased. In that respect, the BAP test, which measures TAC using Vol. 42, No. 2, 2008 thiocyanate that we used in the present study, can become a very useful method to measure TAC in breast milk, since it has a very large range of values. Endogenous antioxidants in breast milk such as CAT, GP, and SOD were thought to increase with the passage of days after birth [24, 25]. It was imagined, therefore, that the TAC in breast milk would increase as the postnatal age in days increased. However, our results showed that TAC tends to decrease with the passage of time. A possible reason why the TACs we measured in this study, which reflect both exogenous and endogenous antioxidants, decreased with the number of days after birth is that the exogenous antioxidants in breast milk decrease with the passage of time, as shown in Table 1. Accordingly, we feel that measuring the TAC in breast milk is useful for comprehensively evaluating the antioxidant capacity of the substances being measured. It is essential to understand that TAC decreases with postnatal age in days. It has been reported that early breast- feeding is important in a number of respects, including the fact that the earlier breastfeeding begins, the lower mortality is [26]; the fact that 8-hydroxy-2'-deoxyguanosine in urine, which is a marker of DNA damage, is lower at two and four weeks after birth in babies who consume breast milk from early on when compared with those who are fed formula milk [27]; and the fact that in a comparison of preterm infants of formula milk versus breast milk in a large scale, multi center study, visual development at the chronological age of six months and language development at 14 months were higher in the cohort of babies who were breastfed for a mean period of 135 ± 118 days (the cohort in which babies’ consumption of milk before hospital discharge was ≥50% breast milk) than those who were fed only formula milk [28]. The possibility that the higher TAC in breast milk in early postnatal age neutralizes oxidative stress for younger babies suggests one reason for these findings. Studies to date on the early oral administration of vitamins aimed at protection from ROS and FR have not produced a consensus on the efficacy of vitamin administration. This may have resulted from the differences between breast- feeding and formula feeding and differences in when the different types of feedings were started. We learned that TAC, which is higher in breast milk than formula milk, decreases with the passage of days. A possible future research topic for improving the prognosis of neonates ( i.e. NEC, CLD, ROP, PVL, IVH and neurological development) could be how to prevent the TAC in breast milk from decreasing with time, as the current study shows that it does, including supplementation with exogenous antioxidants. Breast milk is important to the neonate, who is subjected to a number of FR and ROS. In particular, we believe that starting breastfeeding early is extremely important and useful in protecting against oxidative stress.