Folic acid, a B vitamin also known as folate, is the stable synthetic precursor to the biologically active form of cellular folate (tetrahydrofolate). Low levels of intake have been associated with several negative pregnancy outcomes including neural tube defects, low birth weight and placental abruption.3 Because of its involvement in the synthesis of pyramidines, purines, amino acids and neurotransmitters, the essential role folate plays in maintaining a healthy pregnancy outcome is not surprising. Recognition by the public of folates as a critical nutrient during pregnancy outstrips awareness of all other nutrients, due primarily to the plethora of data backing its efficacy. Observations of the link between folate status and the incidence of neural tube defects (NTD) stimulated numerous controlled clinical trials that demonstrate that folic acid supplied prior to conception can prevent the occurrence and recurrence of NTD.4 The neural tube is an embryonic structure that eventually forms the spinal cord. In patients with NTD, the tube does not close, leading to a variety of neurologically based defects including learning problems and compromised walking. At present the recommended dose of folic acid is 600mcg per day.⁵

Although an effective nutrient, folate?s bioavailability is strongly affected by its delivery vehicle. Studies have generally agreed that the bioavailability of food folates is 20-75 per cent less than that of supplemental, synthetic folic acid.^6,7 Dependent upon the food vehicle, folic acid is somewhat less bioavailable in fortified foods than in tablets. The United States used a crude estimate of 85 per cent bioavailability from folic acid-fortified foods to determine dietary folate equivalents.8 Based on this guide, it was estimated that folic acid taken in fortified foods or taken as a supplement with food is 1.7 times more bioavailable than foods that naturally contain folate.7^,8

Fatty acids enjoy a growing corpus of research literature addressing the health benefits of their components on foetal and postnatal development.9^,10 Foetal survival and development is dependent upon sustained delivery of nutrients across the placenta, often at the expense of those in maternal circulation. Quantitatively, glucose is the most important nutrient crossing the placenta, followed by amino acids.9 Although the transfer and uptake of lipids in utero is small, their importance for foetal development should not be underestimated.

Tissues within the brain, retina and other neural tissues are rich in long chain polyunsaturated fatty acids (LC-PUFAs), some of which are derived from n-6 and n-3 essential fatty acids (EFAs).11 These fatty acids provide the basis for the production of eicosanoids (prostoglandins, prostacyclins, thromboxanes and leukotriens), which are regulators of numerous tissue and cell functions ranging from uterine contractility to blood pressure regulation.

During the period of gestation, research demonstrates a clear correlation between reduced EFA status and reduced neonatal growth.¹² Following supplementation with fish oils during pregnancy, increased levels of DHA have been found in mothers and their newborns.^13,14 Notably, a recent study supplementing seven lactating women with 20g/day flaxseed oil marketed as a vegetarian source of alpha-linolenic acid (LNA)—and ultimately DHA—increased LNA levels, but this did not correlate to an increase in DHA in the women?s milk.15

However, care must be taken with fish oil supplementation as an excess of specific fatty acids may inhibit certain LC-PUFAs via inhibition of delta-6 and delta-5 desaturases that are essential for foetal growth.16 An excess of linoleic acid has been shown to decrease the formation of arachidonic acid.16 Studies indicate that there may be increased bleeding time with fish oil supplementation, although the clinical significance of this is unknown.17 However, in recent studies there is no evidence of this effect even at relatively high doses.18

As a final note, n-3 fish oil supplementation may be a naturally occurring inhibitor of uterine contractions and as such may delay pre-term deliveries without the associated side effects of current pharmacological interventions.19 Although substantial evidence exists for the positive benefits of selected PUFAs during pregnancy, many not covered within this article, the potential risks should also be carefully weighed and further researched when deciding to implement any fatty acid supplements strategy.

Vitamins and minerals
The assessment of vitamin and mineral status during pregnancy is difficult due to the absence of a clearly defined index for evaluating deficiency states. Although there seems to be a trend for declining vitamin and mineral values as gestation advances, this decline may be an artifact of hemodilution and/or alterations in vitamin and mineral carrier molecules.²⁰ However, there are a few vitamins and minerals that do show significant changes during pregnancy, such as folate, where there is a clearly defined reference intake of above 100 per cent RDA. Therefore it is conceivable other nutrients will be found to also show such changes.

Iron stores should be monitored and maintained during gestation. Maternal anaemia has been associated with perinatal and infant mortality rates as well as with premature delivery.²¹ Therefore the maintenance of iron stores should be monitored and maintained during gestation. At particular risk of low-iron status in pregnancy are women with vegetarian diets, because of a lower total intake and low absorption rates of non-heme iron. The total iron cost during pregnancy outside of the 200mg retained by the mother is estimated at around 840mg, which can be dissected as follows:

To prevent iron deficiency and preserve maternal stores, an intake of 9-27mg/day is recommended.²²

Calcium levels that are low in mothers correlate to new-born infants with reduced bone mineral densities, EPH-gestosis (oedema, proteinuria and hypertension) as well as eclampsia.²³ During the latter part of pregnancy (third trimester), the foetus undergoes a period of high calcium accretion somewhere in the order of 300mg/day. This increase is in part due to the up- regulation of placental estrogen on maternal bone resorption and an increased release of parathyroid hormone.24

Mothers with adequate dietary calcium intakes have shown no enhancement of calcium accretion in the neonate.²⁵ Furthering the research dietary calcium may play in foetal health, growth and development, the topic of supplementation has been investigated. In a well-controlled clinical trial, dietary supplementation of 52 pregnant women with 1.5g/day elemental calcium was examined and associated with a lower incidence of pregnancy-induced hypertension.26

On a final note, mothers with multiple pregnancies and low calcium intakes should consider supplementary fortified foods to avoid an increased risk of osteomalacia (softening of bones) in later life.

Vitamin D deficiencies during pregnancy are associated with several disorders suffered by mothers and infants, including neonatal hypocalcemia (low serum calcium), tetany (mineral imbalance causing muscle spasms), and maternal osteomalacia.²⁷ The incidence of deficiency is prevalent among pregnant European (England) and Asian women in places where there are low levels of sunlight as well as poor availability of vitamin D foods, and where there?s little medical advice for increasing intake.²⁸ Supplementation (400IU or 10mcg/day) has been shown as a successful treatment in lowering the incidence of maternal osteomalacia, hypocalcemia and tetany, with higher intakes (25mcg/day) increasing postnatal birth weight and length.²⁹

Iodine provides another example of why avoidance of deficiency is so important in maternal nutrition. Iodine deficiency is directly linked to foetal hypothyroidism or cretinism, often characterised by severe mental retardation.30 Cretinism can be prevented through the use of iodine before and during the first three months of pregnancy. Of the many avoidable illnesses associated with pregnancy and nutrition, the 20 million worldwide that are iodine related could be easily prevented through supplementation, according to the World Health Organization.31 The mean iodine intake by US women of childbearing age is about 170mcg/day,³² yet the recommended intake is 220mcg/day during pregnancy.²⁸

Infant formulas
The importance of postnatal nutrition cannot be over emphasised. The nutritive demands made postpartum (four to six months) are significantly greater than those of pregnancy, as it is a period of rapid growth and development during which infants double the weight accumulated during pregnancy. The significance of early nutrient supply is no more apparent than in the growth, development and composition of the neural system.

The human brain reaches 80 per cent of its total adult weight by the age of 2, whereas whole body weight reaches only 18 per cent, signifying just one aspect of the importance of optimising early postnatal nutrition.

Because of space constraints, this section will cover only three relevant and exciting areas of postnatal nutrition, with a focus on their relevancy to infant formulation.

Prebiotics added to infant formulas has been advocated for the past 20 years in Japan and can be found in at least 90 per cent of commercially available formulations. In contrast, Europeans have only recently applied prebiotic fortification to their infant formulations.33 Breast-fed infants have a higher number of bifidobacteria than bottle-fed infants, who have been considered to have a more complex microbiota that confers multiple benefits rather than just changing the content of one strain.34 Several studies have confirmed this hypothesis over recent years, demonstrating the benefits that breastfeeding can have over formula feeding. The current goal of formulating infant formulas is to reach a composition similar to that of human milk, which contains approximately 1 per cent (weight/volume) neutral oligosaccharides (OSs) and about 0.1 per cent (weight/volume) acidic oligosaccharides.

At present, more than 130 different neutral and acidic OSs have been identified.35 However, there are very few peer-reviewed studies regarding the influence of prebiotics on infant physiology.

A growing catalogue of evidence about human milk OSs such as N-acetly- glucosamine, galactose and fructose oligomers demonstrates the important role of intestinal flora stimulation. Because it?s a new and in some aspects an ethically difficult field of study, there are limited data available regarding the benefits of prebiotics in infant formulations. In the first of only two published studies to date, researchers investigated the influence of a galacto-oligosaccharide (GOS)- and fructo-oligosaccharide (FOS)-containing infant formula on intestinal bacteria.36 Sixty new-born infants received either a 4g or 6g mixture of GOS and FOS/L for one month compared to a placebo. By day 28, a significant dose-dependent increase in bifidobacteria and lactobacilli was observed in faecal measurements than placebo.

A study on pre-term infants given a mixture of short-chain (TOS) and FOS was carried out to meet the molecular size distribution of human milk OSs and to bring about similar prebiotic effects.³⁷ Infants were fed a formula containing 7.2g lactose/dL and supplemented with a mixture of short- (TOS) and long- (FOS) chain prebiotic ingredients (1g/dL). The data demonstrated that prebiotic supplementation resulted in a higher number of beneficial bifidobacteria than infants fed the standard preterm infant formula.

With regard to the safety issues and the wider application of prebiotics for infant formulas in the US, Dr Linda Douglas, manager of scientific affairs at GTC nutrition in Colorado, commented: ?Japanese national surveys of more than 20,000 infants in 1989 and 18,000 infants in 1995 were conducted in order to compare the anthropometric and health data of infants fed these FOS-enhanced formulas with their breastfed counterparts.^38,39 These surveys revealed no detrimental effects from formulas enhanced with short-chain FOS. The data constitutes the largest body of evidence in existence on the safety of short-chain FOS for infant formulas.

?In the US, short-chain FOS are approved for use in foods for infants older than 4 months old. Based on the current regulations, the strength of the Japanese surveys and the history of safe use in that country for infant feeding, the eventual inclusion of short-chain FOS into infant formulas seems likely.?

Protein intake has been recommended during pregnancy to cover the estimated 21g/day deposited in foetal, placental and maternal tissues over the second and third trimesters.⁴⁰ However, what of postnatal recommendations for the infant and the composition of additional proteins in formulas? The currently recommended intake of protein to meet the nutrient requirement of the infant can be seen on page 45. The data provided by the FAO/WHO demonstrates little change in the total intake for body protein equilibrium, since the optimal pattern of essential amino acids changes little between the ages of 6 and 24 months. The Codex Alimentarius does not give any guidelines on what source of protein should be used to meet current recommendations regarding protein intake. It does say, however, that an amino acid score of not less than 70 per cent of casein is advised.

Several studies have shown the effect that different sources of postnatal protein can have on growth and development. When the option of breastfeeding or its continuation for six months is not possible, the use of infant formulas becomes even more important in the delivery of a wide spectrum of amino acids and associated peptides. This issue is further complicated by cows milk protein allergies in the infant and finding a suitable alternative that is as biologically effective as human milk. As mentioned previously, the use of LC-PUFAs and prebiotics play a central role in an effective formula, as does the use of protein in meeting postnatal nutritional needs. Recent studies have shed light on the use of a selection of proteins including rice hydrolysates and whey- and soy-based mixes.

The issues that are still raising concern in finding a successful alternative to human milk is that of the concentration and ratio of constituent amino acids and peptides. These differ markedly from those in soy, rice and whey-based proteins.41

In bovine milk, for example, the ratio of whey to casein is approximately 20:80 but 60:40 in human milk.41 Other dominant protein profiles follow suit; for example, beta-lactoglobulin, the dominant protein found in human milk, is relatively low in formulas. Soy-based mixtures have typically been high in phytic acid, which has led to a decrease in the absorption of vital vitamins and minerals such as iron.42

Hydrosylated rice formulas (HRF) are the latest proteins to be incorporated into formulas for children with dual allergies against bovine and soy-based proteins. Hydrosylated rice has a similar amino acid profile as soy, and in two recent studies it was shown that HRF supports normal growth and adequate metabolic balance.^43,44 These studies, however, have used only small sample sizes and research only over a six-month period. Clearly, more research is needed before any definitive recommendations can be made.

Because of technical advances in protein isolation and extraction methods, the availability of fortified bovine sources of whey and casein are overcoming previous difficulties associated with low concentrations of beta-lactoglobulin, alpha-lactalbumin and tryptophan.41 Similar processing advances in soy-based formulas are leading to a fall in phytic acid concentrations from 300mg/kg to less than 6mg/kg of soy isolate.42 Recent data on dephytinised soy protein isolate and the absorption of mineral and trace elements42 demonstrated zinc was absorbed to a significantly greater extent using the dephytinised formula. However, as phytic acid still remains within the formula, the authors recommend the use of additional iron and ascorbate fortification to compensate for any possible shortfalls in absorption.

Zinc deficiency has been associated with lower infantile birth weights and inversely correlated to the rate of low birth-weight infants.45^,46 Although there seems to be some efficacy in the maintenance and/or monitoring of zinc status before and during pregnancy to prevent deficiency states, little work has directly assessed the influence of zinc on growth or infectious morbidity during the first few months of life. One study compared the supplemental intake of zinc (2.2 mg/kg/day) or placebo over a 12-month period.47 The results demonstrated a significantly greater height gain for the supplemented group over the study period than those taking placebo. A similar study on Chilean infants compared 3mg supplemental zinc (total zinc intake: 1.5-1.8mg/kg/day) or placebo (total zinc intake: 0.7mg/kg/day) for six months.⁴⁸ The results showed both improved growth and significantly greater weight for age scores in the supplemented group.

Although these studies point to favourable outcomes, others show little if any effect of zinc supplementation.49 The difficulty in drawing any comprehensive outcome arises in part because of study design wherein many confounding variables such as bioavailability, timing, compliance and duration of the supplementation period will no doubt influence study outcome. The greatest application and positive data can be recognised in the use of zinc supplementation in low birth weight or small-for-gestational-age infants.

Overall, there seems to be a general trend for improved growth rates suggesting perinatal deficiencies in zinc intake, which can be corrected with postnatal zinc supplementation. The application of supplemental zinc may be best placed as an addition fortification to soy-based formulas that have not been dephytinised.

Infant foods grow up
As one of the fastest-growing functional food sectors, maternal and infant nutrition still has some way to go, scientifically speaking, before we can provide efficacious and safe formulations with known and applicable clinical outcomes. There have been a variety of other potentially applicable nutrients that have been omitted from this article such as botanicals, postnatal lipids, prenatal fish oils, and a selection of vitamins and minerals that have a definite place in infant and maternal health, growth and development. The central argument in this field is whether we need to find supplementation and/or fortification to address dietary deficient states, or if supraphysiological doses of individual or mixed nutrients can provide beneficial and safe clinical outcomes above and beyond currently recommended DRIs.

The future development of functional foods and nutraceuticals may indeed follow the route of nutritional programming as outlined by Dr Das (See ?Science Viewpoint,? below), but due to many invasive procedures needed to assess the efficacy of intervention-based research such as isotope-labelled nutrients, widescale studies may be impossible.

The recent developments in the use of biomarkers are becoming more specific in their ability to link specific interventions to more informative outcomes. This integration of biomarkers into nutrition science offers a real opportunity for the appropriate design of infant formulas and a reduction in study length of long-term epidemiological trials.50

Mark J Tallon, PhD, is chief scientific officer of UK consultancy Oxygenics. www.oxygenix-consultancies.com.
Respond: [email protected]. All correspondences will be forwarded to the author.

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