[Zinc levels in term and preterm milk]

Zinc is an essential element, important for early growth and development, and immune competence, which deficiency might be especially critical in preterm infants. Since published data have shown that some preterm milks have abnormally low zinc values, we decided to measure zinc levels in term and preterm milk, in order to assess if they were within normal values and if there were differences between both groups. Samples from 24 preterm and 20 term mothers (mean gestational age, 30.9 + 0.5 and 39.5 + 0.2 weeks, respectively) were collected and kept at -20 degrees C until analyzed by atomic absorption spectrophotometry, prior wet ashing with nitric acid. Both term and preterm milk showed zinc values within normal levels. No significant differences were registered between them. A decreasing trend was observed along time, which was significant between colostrum and mature milk samples (ANOVA, p < 0.05). In the term group, zinc concentrations in colostrum and mature milk (microgram/mL) (mean +/- SEM) varied between 6.96 +/- 0.69 y 2.44 +/- 0.11, while in the preterm group the values were 6.20 +/- 0.89 y 2.28 +/- 0.54. According to our results, zinc values in human milk were comparable between preterm and term mothers.

Lactoferrin levels in term and preterm milk

OBJECTIVE

Even though there is no doubt that human milk is the best nourishment for the neonate, there is still controversy regarding its suitability for preterm infants. The aim of this study was to contribute to the knowledge of the anti-infective properties of preterm milk, measuring lactoferrin levels, which are a non-specific protective factor.

METHODS

Samples from 26 preterm and 20 term mothers (mean gestational age +/- standard deviation, 30.9+/-2.6 and 39.5+/-1.1 weeks, respectively) were collected during the first month post-partum. Milk samples were obtained by total expression of one breast between 10 a.m. and noon. An aliquot was kept at -20 degrees C until analyzed by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Each sample was run in duplicate.

RESULTS

Lactoferrin levels (X +/- SD) in colostrum and mature milk varied from 575.0+/-218.2 mg/dL to 459.4+/-190.7 mg/dL in preterm samples and from 970.6+/-288.6 mg/dL to 292.0+/-167.4 mg/dL in term samples. No significant differences were observed between preterm and term groups, in spite of the trend observed in colostrum, where term milk tended to show higher levels than preterm milk. Decreasing values were observed in both groups along time (ANOVA, p<0.05). However, in the preterm group, lactoferrin levels seemed to maintain rather constant values from the eighth post-partum day onwards.

CONCLUSIONS

The trend to higher levels of lactoferrin in preterm mature milk would allow maintenance of the protective effect of human milk in preterm infants in spite of the small volumes ingested by these neonates. These findings support the practice of feeding premature infants with their own mothers' milk at a time when their immune systems have not completely developed.

Immunoglobulin M serum levels in females and pups of southern elephant seal (Mirounga leonina) during the suckling period

This paper reports Immunoglobulin M (IgM) levels in serum samples from eight female-pup pairs of southern elephant seals (Mirounga leonina), at King George Island, Antarctica. IgM levels were determined on sera obtained from sequential sampling throughout the suckling period (approximately 23 days). The IgM concentration in southern elephant seal serum was measured by single radial immunodiffusion on agarose plates. Female IgM levels (123.5-613.0 mg/dL, n = 8) were significantly higher than pup levels (5.9-123.6 mg/dL, n = 8). Both groups showed an increasing trend throughout the entire suckling period, with significant differences in relation to stages of lactation. Pup IgM levels on the first day of life (mean +/- SD, 7.6 +/- 2.9 mg/dL, n = 3) suggest that endogenous synthesis takes place before birth.

[Past and present status in the design of infant formulas]

This paper describes briefly the history of infant foods, from the alternate ways of feeding developed during the late 19th century to the present-day infant formulas, and enumerates the different available types (milk-based, soy-based, hypoallergenic, lactose-free, etc,). Among the nutritional aspects the main characteristics of formulation are emphasized, especially within the nitrogen, fat and mineral fractions. Considering the nitrogen fraction, it must be taken into account that the amino acid profiles in milk-based formulas differ according to the casein/whey proteins ratio (either 80:20 or 40:60 in the so-called "adapted" or "humanized"). On the other hand, it has been recognized recently that some non-protein components of human milk, such as taurine, carnitine and nucleotides, are relevant to infant nutrition and therefore, they are being included in some formulas. Regarding fat, essential fatty acids supply is very important; present recommendations stress the importance of providing n-6 to n-3 series ratios close to that found in human milk and also a preformed supply of long-chain polyunsaturated fatty acids. Among minerals, bioavailability and relative proportions of trace elements are important issues in formulation. Other concepts of relevance are the renal solute load and the osmolarity because of their effect on neonate's metabolism.

Immunoglobulin A levels in southern elephant seal (Mirounga leonina) milk during the suckling period

Immunoglobulin A (IgA) levels in milk samples from southern elephant seals at King George Island, Antarctica are reported. IgA levels were determined throughout the suckling period (approximately 23 days). The IgA concentration in southern elephant seal milk was lower than in other mammals and, unlike most mammalian milk, was not high during early lactation. There was not a definite pattern in IgA levels, which fluctuated within narrow limits throughout the suckling period (mean +/- SD, 30.81 +/- 6.38 mg IgA/100 g milk). If IgG was present, its level was too low to be detected by the method used. This is the first evidence in Southern elephant seal of the possibility of transmission of passive immunity after birth involving secretion of IgA in the milk.

Immunoglobulin A level in human milk from mothers delivering preterm

Little information is available on immunoglobulin content of milk from mothers of preterm babies. In this study we have measured IgA levels in samples from preterm and term mothers during the 1st month postpartum. The concentration of IgA tended to be constant in the preterm group (about 251 mg/dl) while it showed a decreasing trend in the term group (from 212.8 +/- 19.9 to 171.6 +/- 12.8 mg/dl). From day 10 onward IgA levels in preterm milk were significantly higher than in term milk (p less than 0.002). These findings support the idea that premature infants fed their own mothers' milk would benefit from more stable levels of IgA, at a time when their mucosal immune system is poorly developed.