Dietary essential fatty acids, long-chain polyunsaturated fatty acids, and visual resolution acuity in healthy fullterm infants: a systematic review

Test-retest reliability of swept visual evoked potential measurements of infant visual acuity and contrast sensitivity

The aim of the study was to describe variations in swept visual evoked potential (SWEEP-VEP) assessment of visual acuity and contrast sensitivity in infants and to evaluate the best way to estimate visual performance from obtained SWEEP-VEP data. The visual performance of 92 infants (6-40 wk of age) was measured in two separate visits. Results were verified with repeated tests in seven adults. There was a strong association between the two measurements of infant visual acuity (r = 0.91, p < 0.001), with no constant bias and an inter-assay coefficient of variation of 8.4%. The intra-assay coefficient of variation was 17% and in repeated sessions all obtained acuity measures were normally distributed, indicating that the mean and not the maximum threshold best estimates visual acuity. This estimate of visual acuity also had lower test-retest variability than those calculated from the maximum threshold or threshold from the average EEG signals (p = 0.001). Test-retest measures of infant contrast sensitivity had a correlation coefficient of 0.72 (p < 0.001) and an inter-assay coefficient of variation of 23%. With the observed test-retest variability, SWEEP-VEP is less valid for estimating the visual performance of individual subjects, but it can give reliable group means. This method was well suited to describe visual development in the infants, which for acuity as well as contrast sensitivity increased by 0.64 octave per doubling in age. However, the variability of the SWEEP-VEP method can be a limiting factor, for example, in the assessment of the potential effect of dietary docosahexaenoic acid in a homogeneous group of infants.

Effect of alpha-linolenic acid supplementation during pregnancy on maternal and neonatal polyunsaturated fatty acid status and pregnancy outcome

BACKGROUND

Maternal essential fatty acid status declines during pregnancy, and as a result, neonatal concentrations of docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) may not be optimal.

OBJECTIVE

Our objective was to improve maternal and neonatal fatty acid status by supplementing pregnant women with a combination of alpha-linolenic acid (ALA, 18:3n-3) and linoleic acid (LA, 18:2n-6), the ultimate dietary precursors of DHA and AA, respectively.

DESIGN

From week 14 of gestation until delivery, pregnant women consumed daily 25 g margarine supplying either 2.8 g ALA + 9.0 g LA (n = 29) or 10.9 g LA (n = 29). Venous blood was collected for plasma phospholipid fatty acid analyses at weeks 14, 26, and 36 of pregnancy, at delivery, and at 32 wk postpartum. Umbilical cord blood and vascular tissue samples were collected to study neonatal fatty acid status also. Pregnancy outcome variables were assessed.

RESULTS

ALA+LA supplementation did not prevent decreases in maternal DHA and AA concentrations during pregnancy and, compared with LA supplementation, did not increase maternal and neonatal DHA concentrations but significantly increased eicosapentaenoic acid (20:5n-3) and docosapentaenoic acid (22:5n-3) concentrations. In addition, ALA+LA supplementation lowered neonatal AA status. No significant differences in pregnancy outcome variables were found.

CONCLUSIONS

Maternal ALA+LA supplementation did not promote neonatal DHA+AA status. The lower concentrations of Osbond acid (22:5n-6) in maternal plasma phospholipids and umbilical arterial wall phospholipids with ALA+LA supplementation than with LA supplementation suggest only that functional DHA status improves with ALA+LA supplementation.

Dose response of bone mass to dietary arachidonic acid in piglets fed cow milk-based formula

BACKGROUND

The addition of arachidonic acid (AA) and docosahexaenoic acid (DHA) to infant formula was recently approved in North America. In piglets, dietary AA is linked to elevations in bone mass.

OBJECTIVE

The objective was to investigate the effects of varied amounts of dietary AA on bone modeling and bone mass with the use of the piglet model for infant nutrition.

DESIGN

Male piglets (n = 32) were randomly assigned to receive 1 of 4 formulas supplemented with AA (0.30%, 0.45%, 0.60%, or 0.75% of fat) plus DHA (0.1% of fat) from days 5 to 20 of life. Measurements included biomarkers of bone modeling, fatty acid status, and whole-body and femur bone mineral content; bone area was measured by dual-energy X-ray absorptiometry. Differences among groups were detected with two-factor analysis of variance. Regression analyses were used to determine factors responsible for bone mineral content after dietary AA was accounted for.

RESULTS

Proportions of AA in plasma, liver, and adipose were modified by the dietary treatments, but bone modeling was not affected. Liver AA was positively related to plasma insulin-like growth factor 1 and calcitriol and urinary N-telopeptide. Whole-body bone mineral content was elevated in the piglets fed 0.60% and 0.75% AA and was best predicted by dietary AA and bone resorption.

CONCLUSIONS

This study confirms that dietary AA alters bone mass and clarifies the best amount of AA to add to the diet of pigs born at term. Because the amount of dietary DHA was held constant, whether other amounts of DHA are related to bone mass requires investigation.

Term infant studies of DHA and ARA supplementation on neurodevelopment: results of randomized controlled trials

Healthy term infants who are not breast-fed may need long-chain polyunsaturated fatty acids (LCPUFA) in their feeding, based on the changes in plasma and tissue fatty composition. However, consistent functional effects across different studies conducted over the past two decades has been more difficult to document. The interpretation of these data has scientific and public interest with the introduction of LCPUFA supplemented formula. There are 14 controlled trials in term infants that have included formula feeding with or without LCPUFA and functional assessment of visual and other measures of neural development; in addition, 7 have evaluated specific measures related to cognitive development. We chose to examine the effect of DHA dose provided daily on the development of visual acuity to explain the differences in visual acuity responses across randomized studies. A "meta-regression" was performed with the use of a DHA effective dose as the independent variable and visual acuity at 4 months as the dependent variable. Since the two main dietary determinants of DHA status are the LNA provided and the preformed DHA consumed, we defined DHA equivalent dose across studies by assuming a 1%, 5%, and 10% conversion of LNA to DHA. Results indicate a strong and significant effect of DHA equivalent dose on magnitude of the visual acuity response at all conversions tested; greatest significance was found when using a 10% bioequivalency (r(2)=0.68, and P=.001). We conclude that there is a significant relation between the total DHA equivalents provided and effectiveness as defined by visual acuity measurements at 4 months of age.

Parenteral fat emulsions based on olive and soybean oils: a randomized clinical trial in preterm infants

OBJECTIVE

To evaluate in premature infants a new parenteral lipid emulsion based on olive and soybean oils (ratio 4:1), with less polyunsaturated fatty acids (PUFA) and more alpha-tocopherol than standard soybean oil emulsion.

STUDY DESIGN

Premature infants (gestational age, 28-<37 weeks) were randomized to receive one of the two emulsions within the first 72 hours of life. The triglyceride dose was increased to 2 g/kg/day within 3 days. Plasma phospholipid fatty acids, alpha-tocopherol/lipid ratio, and urinary malondialdehyde (MDA) excretion were determined at baseline and after 7 days.

RESULTS

Of 45 recruited infants, 33 completed the study per protocol (15 soybean oil, 18 olive oil emulsion). At study end, groups did not differ in plasma phospholipid arachidonic acid, total n-6 and n-3 metabolites, but the olive oil group showed higher values of the PUFA intermediates C18:3n-6 (0.19% +/- 0.01% vs. 0.13% +/- 0.02%, P < 0.05) and C20:3n-6 (2.92% +/- 0.12% vs. 2.21% +/- 0.17%, P = 0.005). The plasma alpha-tocopherol/total lipd ratio was higher in the olive oil group (2.45 +/- 0.27 micromol/mmol vs. 1.90 +/- 0.08 micromol/mmol, P = 0.001), whereas urinary MDA excretion did not differ.

CONCLUSION

The lower PUFA supply with the olive/soybean oil emulsion appears to enhance linoleic acid conversion. The reduced PUFA content, combined with a higher antioxidant intake in the olive oil group, results in an improved vitamin E status. The olive oil-based emulsion is a valuable alternative for parenteral feeding of preterm infants who are often exposed to oxidative stress, while their antioxidative defense is weak.

Infant growth and health outcomes associated with 3 compared with 6 mo of exclusive breastfeeding

BACKGROUND

Opinions and recommendations about the optimal duration of exclusive breastfeeding have been strongly divided, but few published studies have provided direct evidence on the relative risks and benefits of different breastfeeding durations in recipient infants.

OBJECTIVE

We examined the effects on infant growth and health of 3 compared with 6 mo of exclusive breastfeeding.

DESIGN

We conducted an observational cohort study nested within a large randomized trial in Belarus by comparing 2862 infants exclusively breastfed for 3 mo (with continued mixed breastfeeding through >/= 6 mo) with 621 infants who were exclusively breastfed for >/= 6 mo. Regression to the mean, within-cluster correlation, and cluster- and individual-level confounding variables were accounted for by using multilevel regression analyses.

RESULTS

From 3 to 6 mo, weight gain was slightly greater in the 3-mo group [difference: 29 g/mo (95% CI: 13, 45 g/mo)], as was length gain [difference: 1.1 mm (0.5, 1.6 mm)], but the 6-mo group had a faster length gain from 9 to 12 mo [difference: 0.9 mm/mo (0.3, 1.5 mm/mo)] and a larger head circumference at 12 mo [difference: 0.19 cm (0.07, 0.31 cm)]. A significant reduction in the incidence density of gastrointestinal infection was observed during the period from 3 to 6 mo in the 6-mo group [adjusted incidence density ratio: 0.35 (0.13, 0.96)], but no significant differences in risk of respiratory infectious outcomes or atopic eczema were apparent.

CONCLUSIONS

Exclusive breastfeeding for 6 mo is associated with a lower risk of gastrointestinal infection and no demonstrable adverse health effects in the first year of life.

Visual function in breast-fed term infants weaned to formula with or without long-chain polyunsaturates at 4 to 6 months: a randomized clinical trial

OBJECTIVE

Breast-fed infants receive docosahexaenoic acid (DHA) and arachidonic acid (ARA) in their diet. Upon weaning, infants lose this dietary source of long-chain polyunsaturates because many commercial formulas do not contain these important constituents for neural membrane biogenesis. We evaluated the benefits of postweaning dietary supplementation of DHA + ARA on visual maturation.

STUDY DESIGN

Healthy term infants (n = 61) were breast-fed to 4 to 6 months, then were randomly assigned to commercial formula or formula supplemented with DHA (0.36%) + ARA (0.72%). Measurements of red blood cell (RBC) fatty acids, visually evoked potential (VEP) acuity, and stereoacuity were done before and after weaning.

RESULTS

At 1 year of age, RBC-DHA in the commercial formula-fed group was reduced by 50% from the weaning level, whereas there was a 24% increase in the DHA + ARA-supplemented group. The primary outcome measure, VEP acuity, was significantly more mature in supplemented infants at 1 year of age. Elevated RBC-DHA levels were associated with more mature VEP acuity. There were no significant diet-related differences in stereoacuity.

CONCLUSIONS

These data extend through the first year of life the critical period in which a dietary supply of DHA and ARA can contribute in optimizing visual development in term infants.

Advances in nutritional modifications of infant formulas

Modifications to infant formulas are continually being made as the components of human milk are characterized and as the nutrient needs of diverse groups of infants are identified. Formulas with long-chain polyunsaturated fatty acids added in amounts similar to those in human milk have recently become available in the United States; infants fed these formulas or human milk have higher tissue concentrations of long-chain polyunsaturated fatty acids and reportedly have better visual acuity than do infants fed nonsupplemented formulas. Selenium, an important antioxidant, is present in higher concentrations in human milk than in non-fortified cow milk-based formula, and the selenium intakes of infants fed nonfortified formulas are reported to be at or below recommended levels. Blood selenium concentrations and plasma glutathione peroxidase activity are higher in infants fed selenium-supplemented formulas or human milk than in infants fed non-fortified formulas. Nucleotides and their related products play key roles in many biological processes. Although nucleotides can be synthesized endogenously, they are considered "conditionally essential." Nucleotide concentrations in human milk are higher than in unsupplemented cow milk-based formulas, and studies in animals and human infants suggest that dietary nucleotides play a role in the development of the gastrointestinal and immune systems. Formulas for preterm infants after hospital discharge are designed to meet the needs of a population in whom growth failure is common. Several studies have shown that preterm infants fed nutrient-enriched formulas after hospital discharge have higher rates of catch-up growth than do infants fed standard term-infant formulas.

Efficacy and safety of docosahexaenoic acid and arachidonic acid addition to infant formulas: can one buy better vision and intelligence?

Long chain polyunsaturated fatty acids (LCPUFA) namely arachidonic acid (ARA, 20:4n-6) and docosahexaenoic acid (DHA, 22:6n-3) are highly concentrated in the phospholipid bilayer of biologically active brain and retinal neural membranes and are important in phototransduction and neuronal function. The rationale for adding these LCPUFA to infant formula (IF) was primarily because of their presence in large quantities in the retina and brain and in human milk. In addition, infants fed IF containing LCPUFA and breastfed infants have comparable ARA and DHA levels in red cell and plasma, in contrast to the lower ARA and DHA levels in those fed IF containing only the essential fatty acids: linoleic (LA, 18:2n-6) and linolenic (LNA, 18:3n-3), the precursors to ARA and DHA, respectively. However, functional benefits in particular visual or neural development from IF containing LCPUFA remains controversial. Potential for excessive and/or imbalanced intake of n-6 and n-3 fatty acids exists with increasing fortification of LCPUFA to infant foods other than IF.

The potential role for arachidonic and docosahexaenoic acids in protection against some central nervous system injuries in preterm infants

The risk of central nervous, visual, and auditory damage increases from 2/1000 live births in the normal birthweight to > 200/1000 as birthweight falls below 1500 g. Such babies are most likely to be born preterm. Advances in infant care have led to increasing numbers of very-low-birthweight, preterm infants surviving to school age with moderate to severe brain damage. Steroids are one of the current treatments, but they cause significant, long-term problems. The evidence reported here suggests an additional approach to protecting the very preterm infant by supporting neurovascular membrane integrity. The complications of preterm, very-low-birthweight babies include bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular hemorrhage, periventricular leukomalacia, and necrotizing enterocolitis, all of which have a vascular component. Arachidonic acid (AA) and DHA are essential, structural, and functional constituents of cell membranes. They are especially required for the growth and function of the brain and vascular systems, which are the primary biofocus of human fetal growth. Molecular dynamics and experimental evidence suggest that DHA could be the ligand for the retinoid X receptor (RXR) in neural tissue. RXR activation is an obligatory step in signaling to the nucleus and in the regulation of gene expression. Very preterm babies are born with minimal fat stores and suboptimal circulating levels of these nutrients. Postnatally, they lose the biomagnification of the proportions of AA and DHA by the placenta for the fetus. No current nutritional management repairs these deficits. The placental biomagnification profile highlights AA rather than DHA. The resultant fetal FA profile closely resembles that of the vascular endothelium and not the brain. Without this nourishment, cell membrane abnormalities would be predicted. We present a scientific rationale for a common pathogenic process in the complications of prematurity.

Assessment of essential fatty acid and omega3-fatty acid status by measurement of erythrocyte 20:3omega9 (Mead acid), 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3

BACKGROUND

Early suspicion of essential fatty acid deficiency (EFAD) or omega3-deficiency may rather focus on polyunsaturated fatty acid (PUFA) or long-chain PUFA (LCP) analyses than clinical symptoms. We determined cut-off values for biochemical EFAD, omega3-and omega3/22:6omega3 [docosahexaenoic acid (DHA)]-deficiency by measurement of erythrocyte 20:3omega9 (Mead acid), 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3, respectively.

METHODS

Cut-off values, based on 97.5 percentiles, derived from an apparently healthy omnivorous group (six Dominica breast-fed newborns, 32 breast-fed and 27 formula+LCP-fed Dutch low-birth-weight infants, 31 Jerusalem infants, 33 Dutch 3.5-year-old infants, 69 omnivorous Dutch adults and seven Dominica mothers) and an apparently healthy group with low dietary LCP intake (81 formula-fed Dutch low-birth-weight infants, 12 Dutch vegans). Cut-off values were evaluated by their application in an EFAD suspected group of 108, mostly malnourished, Pakistani children, three pediatric patients with chronic fat-malabsorption (abetal-ipoproteinemia, congenital jejunal and biliary atresia) and one patient with a peroxisomal beta-oxidation disorder.

RESULTS

Erythrocyte 20:3omega9, 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3 proved age-dependent up to 0.2 years. Cut-off values for ages above 0.2 years were: 0.46mol% 20:3omega9 for EFAD, 0.068mol/mol 22:5omega6/20:4omega6 for omega3-deficiency, 0.22mol/mol 22:5omega6/22:6omega3 for omega3/DHA-marginality and 0.48mol/mol 22:5omega6/22:6omega3 for omega3/DHA-deficiency. Use of RBC 20:3omega9 and 22:5omega6/20:4omega6 cut-off values identified 20.4% of the Pakistani subjects as EFAD+omega3-deficient, 12.9% as EFAD+omega3-sufficient, 38.9% as EFA-sufficient+omega3-deficient and 27.8% as EFA-sufficient+omega3-sufficient. The patient with the peroxisomal disorder was classified as EFA-sufficient, omega3-sufficient (based on RBC 22:5omega6/20:4omega6) and omega3/DHA-deficient (based on RBC 22:5omega6/22:6omega3). The three other pediatric patients were classified as EFAD, omega3-deficient and omega3/DHA-deficient.

CONCLUSION

Use of the combination of the present cut-off values for EFA, omega3 and omega3/DHA status assessment, as based on 97.5 percentiles, may serve for PUFA supplement intervention until better concepts have emerged.

Sows' milk attenuates dexamethasone-induced reductions in liver docosahexaenoic acid

The objective was to determine the effects of dexamethasone (Dex) on growth and arachidonic (AA) and docosahexaenoic (DHA) acid status. Piglets were randomized to suckling or formula feeding plus Dex or placebo treatment for 15 days. Weight and length at the beginning and end of study was used to assess growth. After 15 days, AA and DHA in phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were measured in liver and plasma and total AA and DHA in forebrain and brainstem. Dex treatment significantly reduced weight and length. Dex reduced liver PC and PE DHA in the formula group, but the reduction in the suckled group was not significant. PC AA and DHA were positively related in liver and plasma. A main effect of Dex to reduce AA and DHA was observed in forebrain but not in brainstem. Sows' milk attenuated the Dex-induced reduction in liver DHA but not forebrain AA and DHA or somatic growth.

Lipids with an emphasis on long-chain polyunsaturated fatty acids

In addition to their role as a source of energy, several fatty acids are important components of cell membranes and/or precursors of biologically important eicosanoids. The long-chain polyunsaturated fatty acids, docosahexaenoic acid (DHA) and arachidonic acid (AA), are important for optimal visual function and neurodevelopment. These fatty acids are present in human milk but, until recently, have not been included in formulas marketed in the United States. Although the results of clinical trials assessing the effect of DHA and AA intakes on visual and cognitive development have been inconsistent, some studies suggest benefits. Adequate intake of these fatty acids may be especially important for the preterm infant.

Estimated biological variation of the mature human milk fatty acid composition

We estimated the biological variation (CV(biol)) of 28 fatty acids (FA) in 465 mature human milk samples from The Netherlands, Caribbean, Jerusalem, Tanzania and Pakistan, by using data from the observed variation (CV(obs)) and analytical variation (CV(anal)). CV(biol) of the various regions was remarkably similar. The average CV(biol) of 455 samples, Pakistan excluded, ranged from 12.7% for 16:0 and 18.9% for 18:1 omega 9 to 68% for 22:6 omega 3 and about 100% for 20:5 omega 3. Those of 20:4 omega 6, 18:2 omega 6 and 18:3 omega 3 were 28.0, 33.0 and 37.3%, respectively. Because of the large CV(biol) and the many dietary changes in recent history, it seems impossible to consider the present human milk FA composition as the 'gold standard' for infant formula. Optimal human milk FA composition should rather derive from populations that consume traditional diets or from the scientific data that show the function of the individual FAs in neonatal development.

Fluctuations in human milk long-chain PUFA levels in relation to dietary fish intake

Within the Danish population, milk DHA (22:6n-3) levels vary by more than a factor of 10. This paper deals with fluctuations in the milk content of 22:6n-3 and other long-chain PUFA (LCPUFA) and the acute effects of fish meals and fish oil supplements on milk levels of LCPUFA. Twelve fish-eating mothers with 4-mon-old infants provided one blood and one adipose tissue sample, and seven consecutive morning hind-milk samples with dietary records from the previous days. Another 12 lactating women were given fish oil (2-8 g) for breakfast and delivered 6-12 milk samples during the following 24 h. The mean milk 22:6n-3 content of the fish-eating mothers was 0.57+/-0.28 FA% (= percentage of total area of FAME peaks in GLC) and the day-to-day variation (SD/mean) within the individual was 35+/-17%. Mean milk 22:6n-3 content on mornings with no fish the day before was 0.42+/-0.15 FA%; this was increased by 82+/-17% (n = 9, P = 0.05) if the mother had eaten fatty fish. Fish oil resulted in a twofold increase in milk 22:6n-3 levels, which peaked after 10 h and lasted for 24 h. The EPA content of milk was also increased by fish meals and fish oil supplements, but these had no effect on the level of arachidonic acid. The study showed that diurnal and day-to-day fluctuations in levels of milk n-3 LCPUFA are large, which makes it difficult to assess the 22:6n-3 intake of breast-fed infants from a single milk sample. In studies of the functional outcome of dietary 22:6n-3 in breast-fed infants it is suggested also to use a measure of maternal 22:6n-3 status.

Fatty acid formula supplementation and neuromotor development in rhesus monkey neonates

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is highly concentrated in CNS tissues. Although breast milk contains the fatty acids DHA and arachidonic acid, infant formulas marketed in North America do not contain these nutrients. The potential deleterious effects of rearing infants with formulas devoid of these nutrients was assessed by comparing nursery-reared rhesus macaque infants (Macaca mulatta) fed standard formula with infants fed standard formula supplemented with physiologically relevant concentrations of DHA (1.0%) and arachidonic acid (1.0%). Neurobehavioral assessments were conducted on d 7, 14, 21, and 30 of life using blinded raters. The 30-min assessment consisted of 45 test items measuring orienting, temperament, reflex capabilities, and motor skills. Plasma concentrations of DHA in standard formula-fed infants were significantly lower than those fed supplemented formula or mother-raised (breast-fed) infants; however, infants fed the supplemented formula exhibited higher arachidonic acid levels than either mother-reared infants or infants fed standard formula. Infant monkeys fed the supplemented formula exhibited stronger orienting and motor skills than infants fed the standard formula, with the differences most pronounced during d 7 and 14. This pattern suggests an earlier maturation of specific visual and motor abilities in the supplemented infants. Supplementation did not affect measures of activity or state control, indicating no effect on temperament. These data support the assertion that preformed DHA and arachidonic acid in infant formulas are required for optimal development.

The n-3 and n-6 polyunsaturated fatty acid composition of plasma phospholipids in pregnant women and their infants. relationship with maternal linoleic acid intake

The availability of long-chain polyunsaturated fatty acids during infancy has been related to neonatal growth and development. Fatty acid concentration at birth is an important predictor of postnatal level. The primary aim of this study was to provide a description of the distribution of n-3 and n-6 polyunsaturated fatty acids in the plasma phospholipid fraction of pregnant women remaining on a Western-style diet and their neonates. The plasma phospholipid polyunsaturated fatty acid composition was determined by gas-liquid chromatography in 889 mother-infant pairs. Blood samples were taken during the first, second and third trimester of pregnancy, at delivery, and from the umbilical vein at birth. Mean (+/- SD) fatty acid concentrations are reported in mg/l and as percentage of total fatty acids (% wt/wt). In addition, the 10th, 25th, 50th, 75th and 90th percentiles are given. The distribution of docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6) concentrations in umbilical plasma phospholipids is also reported as a function of gestational age and maternal linoleic acid intake during pregnancy. This data can be be used as a reference for future studies and may aid in identifying term infants with a relatively low long-chain polyene status at birth.

Docosahexaenoic acid and arachidonic acid in infant development

Docosahaxaenoic acid and arachidonic acid are highly concentrated in the central nervous system. The amount of these fatty acids in the central nervous system increases dramatically during the last intrauterine trimester and the first year of life. A central question of research conducted during the past 20 years is if the essential fatty acid precursor of docosahexaenoic acid is sufficient to achieve optimal DHA accumulation in the central nervous system and, therefore, infant development. The important role of non-human primate studies in characterising the behavioral effects of n-3 essential fatty acid deficiency and subsequent low brain DHA accumulation, the difference between essential fatty acid deficiencies and conditional deficiencies of docosahexaenoic acid and arachidonic acid, and the evidence that human infants have a conditionally essential need for docosahexaenoic acid and, perhaps, for arachidonic acid are summarised. The current suggestive evidence for several possible mechanisms underlying behavioral effects are also provided.

Mechanisms of action of docosahexaenoic acid in the nervous system

This review describes (from both the animal and human literature) the biological consequences of losses in nervous system docosahexaenoate (DHA). It then concentrates on biological mechanisms that may serve to explain changes in brain and retinal function. Brief consideration is given to actions of DHA as a nonesterified fatty acid and as a docosanoid or other bioactive molecule. The role of DHA-phospholipids in regulating G-protein signaling is presented in the context of studies with rhodopsin. It is clear that the visual pigment responds to the degree of unsaturation of the membrane lipids. At the cell biological level, DHA is shown to have a protective role in a cell culture model of apoptosis in relation to its effects in increasing cellular phosphatidylserine (PS); also, the loss of DHA leads to a loss in PS. Thus, through its effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Finally, progress has been made recently in nuclear magnetic resonance studies to delineate differences in molecular structure and order in biomembranes due to subtle changes in the degree of phospholipid unsaturation.

Recent advances in infant cognition: implications for long-chain polyunsaturated fatty acid supplementation studies

The assessment of cognitive function in early life has recently become an issue for consideration in long-chain polyunsaturated fatty acid (LC-PUFA) supplementation studies. This article reviews the various means by which such assessment has been done in past LC-PUFA supplementation studies and provides some background on recent advances in the measurement of infant cognition that may need to be considered when planning or designing future supplementation studies. These include (i) consideration of the specificity of LC-PUFA effects on cognition, (ii) inclusion of multiple tasks or levels of measurement as outcome measures, and (iii) a stronger emphasis on developmental processes in the design of such studies.

Essential fatty acids in visual and brain development

Essential fatty acids are structural components of all tissues and are indispensable for cell membrane synthesis; the brain, retina and other neural tissues are particularly rich in long-chain polyunsaturated fatty acids (LC-PUFA). These fatty acids serve as specific precursors for eicosanoids, which regulate numerous cell and organ functions. Recent human studies support the essential nature of n-3 fatty acids in addition to the well-established role of n-6 essential fatty acids in humans, particularly in early life. The main findings are that light sensitivity of retinal rod photoreceptors is significantly reduced in newborns with n-3 fatty acid deficiency, and that docosahexaenoic acid (DHA) significantly enhances visual acuity maturation and cognitive functions. DHA is a conditionally essential nutrient for adequate neurodevelopment in humans. Comprehensive clinical studies have shown that dietary supplementation with marine oil or single-cell oil sources of LC-PUFA results in increased blood levels of DHA and arachidonic acid, as well as an associated improvement in visual function in formula-fed infants matching that of human breast-fed infants. The effect is mediated not only by the known effects on membrane biophysical properties, neurotransmitter content, and the corresponding electrophysiological correlates but also by a modulating gene expression of the developing retina and brain. Intracellular fatty acids or their metabolites regulate transcriptional activation of gene expression during adipocyte differentiation and retinal and nervous system development. Regulation of gene expression by LC-PUFA occurs at the transcriptional level and may be mediated by nuclear transcription factors activated by fatty acids. These nuclear receptors are part of the family of steroid hormone receptors. DHA also has significant effects on photoreceptor membranes and neurotransmitters involved in the signal transduction process; rhodopsin activation, rod and cone development, neuronal dendritic connectivity, and functional maturation of the central nervous system.

Considerations in planning vegan diets: infants

Appropriately planned vegan diets can satisfy nutrient needs of infants. The American Dietetic Association and The American Academy of Pediatrics state that vegan diets can promote normal infant growth. It is important for parents to provide appropriate foods for vegan infants, using guidelines like those in this article. Key considerations when working with vegan families include composition of breast milk from vegan women, appropriate breast milk substitutes, supplements, type and amount of dietary fat, and solid food introduction. Growth of vegan infants appears adequate with post-weaning growth related to dietary adequacy. Breast milk composition is similar to that of non-vegetarians except for fat composition. For the first 4 to 6 months, breast milk should be the sole food with soy-based infant formula as an alternative. Commercial soymilk should not be the primary beverage until after age 1 year. Breastfed vegan infants may need supplements of vitamin B-12 if maternal diet is inadequate; older infants may need zinc supplements and reliable sources of iron and vitamins D and B-12. Timing of solid food introduction is similar to that recommended for non-vegetarians. Tofu, dried beans, and meat analogs are introduced as protein sources around 7-8 months. Vegan diets can be planned to be nutritionally adequate and support growth for infants.

Long-chain polyunsaturated fatty acids in infant nutrition: effects on infant development

In the past year, two groups of investigators reported the effects of feeding n-3 and n-6 long chain polyunsaturated fatty acids on term-infant development. In general, these small randomised studies, along with two recent large randomised clinical trials, one with preterm and one with term infants, confirm and extend data on efficacy from smaller clinical studies reported in the past ten years. In addition, two independent systematic reviews published this year evaluated all but the most recent studies. Both systematic reviews concluded that there were benefits of feeding long chain polyunsaturated fatty acids to preterm infants in the short-term and acknowledged the absence of studies to address their effects on long-term visual development in infants. The continuing controversy as to the need for long chain polyunsaturated fatty acids by term infants is highlighted by the different conclusions reached in the systematic reviews. A middle view can also be supported by the data; that is, that fewer term infants than preterm infants can benefit from these fatty acids because of greater long chain polyunsaturated fatty acid accumulation in utero. Differences in intrauterine accumulation of these fatty acids may also play a role in inconsistent results among term studies.

The role of polyunsaturated fatty acids in term and preterm infants and breastfeeding mothers

DHA and AA, which are components of breast milk but not infant formulas marketed in the United States and some other countries, are important components of the brain, and DHA is a major component of the retina. Also, many studies have demonstrated advantages of breastfeeding versus formula-feeding on subsequent cognitive and visual function; however, available data are insufficient to justify the conclusion that the presence of DHA and AA in breast milk is partially or soley responsible for the apparent advantages of breastfeeding. On the other hand, many studies of DHA (and AA)-supplemented versus unsupplemented formulas have shown clear advantages of the supplemented formulas on visual acuity at 2 and 4 months of age or neurodevelopmental status at 12 to 18 months of age. Although one logically may assume that these early effects may have long-term effects, this assumption is not warranted by the available data. One of the major problems is the difficulty of assessing visual and cognitive function of infants. Scores on standard neurodevelopmental tests at 1 year of age, for example, are only weakly correlated with performance at school age (when more definitive assessments are possible), and little is known about the predictability of later visual function from behavioral or electrophysiologic assessments of visual function early in life. Even prematurely born infants can synthesize DHA and AA and other omega-3 and omega-6 LC-PUFAs from the dietary EFAs, LA and ALA. Nonetheless, plasma, erythrocyte and brain lipid levels of DHA are lower in infants whose diets do not contain DHA. Whether more optimal intakes of ALA result in higher plasma and tissue levels of this FA is unclear. The breast-milk content of LC-PUFAs is not regulated by the mammary gland but, rather, reflects the concentrations of LC-PUFAs in maternal plasma lipids that, in turn, are dependent on maternal diet and, probably, maternal activities of the desaturases and elongases involved in converting dietary LA and ALA to LC-PUFAs. This occurrence suggests that some infants receive sufficient LC-PUFA to support normal rates of deposition, whereas others may not. Also, some infants probably can synthesize additional LC-PUFAs from the LA and ALA contents of human milk. Thus, depending on maternal diet and maternal and infant desaturase and elongase activities, some breastfed infants may receive less than adequate LC-PUFAs to support normal rates of deposition. Clearly, the role of LC-PUFAs in infant development is not a simple issue. Also, no foolproof method exists to ensure an adequate but not excessive intake. Thus, because some evidence shows that dietary LC-PUFA (DHA, AA, or both) as components of breast milk or formula confers at least transient developmental benefits, supplementation of infant formulas with LC-PUFAs is supportable provided that the supplements used are safe. The safety of all available supplements is unknown; however, some trials reveal few reasons for major concerns about the safety of single-cell oils, low-EPA fish oil, or egg-yolk phospholipid or triglyceride fractions.

Meta-analysis of dietary essential fatty acids and long-chain polyunsaturated fatty acids as they relate to visual resolution acuity in healthy preterm infants

OBJECTIVE

To derive combined estimates of visual resolution acuity differences between healthy preterm infants consuming different compositions and ratios of essential fatty acids (EFAs) and docosahexaenoic acid (DHA), an omega-3 (n-3) long-chain polyunsaturated fatty acid (LCPUFA).

DATA SOURCES

Electronic biomedical reference database (Medline and Health Star from 1965 to July 1999) searches with index terms omega-3, n-3, infant, vision, acuity, and human. Current review article, monograph, and book chapter bibliography/reference section hand searches.

STUDY SELECTION

A total of 5 original articles and 4 review chapters were reviewed for details on study design, conduct, and outcome. Four prospective trials of EFA/LCPUFA supplementation were included in these analyses. For behaviorally based outcomes, there were 2 randomized comparisons each at </=1, 2, 6, 9, and 12 months of corrected age and 4 randomized comparisons at 4 months of corrected age. For electrophysiologically based outcomes (visual-evoked potential), there were 2 randomized comparisons each at </=1 and approximately 4 months of corrected age.

DATA EXTRACTION

Dietary composition and EFA/LCPUFA balance, study design, and analytic characteristics (duration of feeding, source of EFAs/LCPUFAs, number of subjects in study population, number of subjects analyzed, and basis for estimating age), and experiment-based characteristics (location, number or sites, design, vision tests employed, testing protocol, and ophthalmic examination) were recorded independently by 2 researchers with a standardized protocol.

DATA SYNTHESIS

The relative difference in visual resolution acuity between groups of infants who received a source of dietary EFAs/LCPUFAs and groups who did not was computed and then analyzed with the DerSimonian and Laird random-effects method.

RESULTS

Analysis of the randomized comparisons (DHA-supplemented formula vs DHA-free formula) showed significant differences in visual resolution acuity at 2 and 4 months of age. Combined estimates of behaviorally based visual resolution acuity differences at these ages were.47 +/-.14 octaves and.28 +/-.08 octaves, respectively. A 1-octave difference is a reduction in the width of the stimulus elements by 50%.

CONCLUSION

These results support efficacy of n-3 LCPUFA intake in early visual system development, although supplementation safety issues still must be addressed through larger randomized trials. Whether n-3 intake confers lasting advantage in visually based process development across the life-span is still to be determined.