Docosahexaenoic acid and arachidonic acid in infant development

Semin Neonatol 2001; 6: 437–449 doi:10.1053/siny.2001.0093, available online at http://www.idealibrary.com on

Docosahexaenoic acid and arachidonic acid in infant development Susan E. Carlson

University of Kansas Medical Center, Departments of Dietetics and Nutrition (School of Allied Health) and Pediatrics (School of Medicine), Kansas City, KS, USA

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.  2002 Elsevier Science Ltd

What are docosahexaenoic acid and arachidonic acid? Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6), respectively, are the members of the n-3 and n-6 fatty acid families found in the highest concentrations in cell membranes. Because the accumulation of these fatty acids in cell membranes is influenced by the kind and amount of n-3 and n-6 fatty acids in the diet, there exists at least the potential for these fatty acids in the diet to influence all physiological functions. Brain and retina contain large quantities of DHA and AA [1,2], and most functional studies of DHA and AA status have measured either visual or central nervous system outcomes. This article focuses on these kinds of functions in relation to DHA and AA status. Studies of other physiological effects of DHA and AA status, especially as Correspondence to: Susan E. Carlson, University of Kansas Medical Center, Department of Dietetics and Nutrition, 4019 Delp, 3901 Rainbow Blvd, Kansas City, KS 66160, USA. Tel.: +1 913 588 5359; Fax: +1 913 588 8946; E-mail: [email protected]

1084–2756/01/$-see front matter

modifiable by DHA and AA during development, are needed.

Normal accumulation of DHA and AA in human retina and brain DHA constitutes about 30% of the ethanolamine and serine phosphoglycerides of neuronallyenriched tissue in the brain (gray matter) [1] and about 45% of these same phosphoglycerides in the retina of all mammalian species [2]. In the brain, DHA is especially concentrated in membranes surrounding synapses [3]. In the retina, both synaptic regions in the neural retina and the disk membranes of the photoreceptors are highly enriched in DHA [2]. During the last intrauterine trimester [4,5] and the first 18 months of human postnatal life [5], DHA and AA accumulate rapidly in the central nervous system. The accumulation occurs in part because of transfer of preformed DHA and AA from the mother to the fetus in utero [6]. After birth, © 2002 Elsevier Science Ltd

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these fatty acids continue to be transferred from the mother to the infant who is fed human milk for the duration of milk feeding [7,8]. Infants can also synthesize DHA and AA from their respective essential fatty acid precursors,
-linolenic acid (18:3n-3) and linoleic aid (18:2n-6) [9–12]. Both early birth [4,5] and milk substitutes [7,8] reduce the normal physiological transfer of DHA from mother to offspring. As a consequence, some investigators in the early 1980s asked if human infants could achieve optimal DHA and AA status by synthesis from essential fatty acids in the absence of intrauterine transfer or postnatal human milk intake. This question led to the first clinical studies. Several lines of investigation during the past 20 years have contributed to our current understanding of the functional importance of DHA and AA for visual and central nervous system function. Animal studies provided the first evidence that changes in retinal and brain DHA could alter neural function. Descriptive studies in the late 1970s and early 1980s of infants fed diets with (human milk) or without (infant formula) DHA provided the first evidence that early diet could alter DHA status of infants [7,8] and that the addition of DHA to formula could enhance DHA status of infants [13–15]. More recent descriptive studies confirmed the early hypothesis that lower brain DHA accumulation occurs when human infants are born significantly before term or are fed diets without DHA and AA after birth [16–19]. Randomized clinical studies of infants fed diets with variable amounts of essential fatty acids or LCPUFA demonstrated that plasma and red blood cell fatty acids were influenced by fatty acid intake [14,15]. As will be discussed, these and many other subsequent studies demonstrated that some functional measures reflecting different behavioral domains were related to DHA status. More recently, animal models and model systems are being used to elucidate the biophysical and biochemical bases for changes in behavior that occur when brain LCPUFA are varied.

Effects of essential fatty acid deficiency on brain composition and function Much of what we know about the roles of DHA and AA comes from studies in which animals

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were deprived of one or both of their essential fatty acid precursors. Diets deficient in linoleic acid result in less n-6 LCPUFA in brain, but overall growth, including brain growth, is less than in the absence of n-6 fatty acid deficiency [20]. With lower brain growth, it is not surprising that behaviors are affected as has been shown previously for diets deficient in linoleic acids [see 21 for review]. Diets deficient in
-linolenic acid but that contain linoleic acid do not result in less growth than normal, however, they do lead to lower accumulation of DHA in brain phospholipids [22–26]. With the lesser accumulation of DHA, a reciprocal increase in docosapentaenoic acid (DPA, 22:5n-6) from the n-6 family of fatty acids occurs in cell membranes including those of the brain [22–26]. Despite normal brain growth, these structural changes in CNS membranes are related to changes in behavior [see 21,27 for reviews]. As noted before, the transfer of maternal DHA from mother to her offspring provides one of the main sources of DHA to the offspring. Humans receive maternal LCPUFA in utero and in milk feeding after birth [4,5,7,8] while rats receive most transfer of DHA to brain after birth [28]. The degree of brain development at birth among species has been exploited to develop model systems to study the relationship between essential fatty acid intake and LCPUFA accumulation and function. For example, brain development in rat pups is most analogous to development in human infants born at the beginning of the 3rd trimester of pregnancy [4,5,28], while brain development in the newborn pig is most comparable to that of infants born at term [29]. Monkey infants have been exposed to n-3 fatty acid-deficient diets both in utero and after birth to produce different degrees of DHA depletion in retina and brain so as to approximate degrees of brain DHA found in human infants [27]. Behavioral studies in non-human primates have been especially helpful in suggesting functional outcomes for investigations of adequacy of LCPUFA status in human infants. Although nonhuman primate studies will be emphasized here, a larger body of data on LCPUFA and behavior comes from studies with rodents [see 21 for review]. Animal studies have helped identify the behavioral domains that might be sensitive to the quality and quantity of LCPUFA accumulation in brain.

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Brain DHA and animal behavior A number of behavioral effects of n-3 fatty acid deficiency have been identified in rhesus monkeys. Those exposed to n-3 fatty acid-deficient diets in utero and after birth had lower DHA accumulation in retina and brain [23,30] and abnormal retinal function [23] and visual acuity [30] in the visual system, smaller a-wave amplitudes were observed initially, but these corrected by 2 years of age [31]. On the other hand, the visual function of deficient animals continued to differ from the control group with longer implicit times and relative refractory periods [31]. These differences became more pronounced with age [31] and were not corrected even when the retinal and cerebral cortex DHA were returned to normal at 10 months of age or later by feeding n-3 LCPUFA [32]. Infant monkeys developed abnormal electroretinograms even when they were not exposed to an
-linolenic acid deficient diet until birth [33]. This has implications for human visual development given that the visual system of newborn monkeys is more developed than that of term human infants [31]. Rhesus monkeys which are n-3 deficient have been shown to have longer duration looks in tests of visual attention in comparison to monkeys with higher brain DHA [34]. Although the known effects of DHA deficiency on visual function could influence attention, the investigators reported that the effects on look duration were unrelated to visual acuity [35]. Similarly, preterm human infants fed formulas with DHA, and presumed to have higher brain DHA accumulation compared to infants fed diets without DHA, have been shown to have higher visual acuity [36,37] and shorter look duration during the test phase of the Fagan Test of Infant Intelligence [38,39]. However, like the rhesus monkey model, visual acuity was not related to look duration [40]. Both monkeys and human infants in these studies were tested on a task that also provided information about novelty preference, however, in neither monkeys nor human infants was higher DHA status related to higher novelty preference [34,38,39]. Novelty preference and look duration are believed to measure different underlying neural processes [41]. Interestingly, the largest RCT to compare preterm infants fed formulas with and without DHA and AA, found that infants who received the LCPUFA-containing formula had a higher novelty preference during the Fagan Test but did not find an effect on look duration [42].

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Thus, at present, there is evidence that DHA and AA status may influence both look duration and novelty preference and the neural processing that contribute to these behaviors. Look duration decreases with age, an apparent maturational effect that has been attributed to faster processing speed, a cognitive effect [43,44]. Alternative explanations for relatively shorter look duration included an increased ability to disengage attention [45], and lower reactivity [46]. Each of these possible explanations suggests a positive effect of higher brain DHA accumulation on development. In the nonhuman primate, the evidence is more in favor of effects on reactivity than cognition. Reisbick et al. [46,47] described higher frequency of stereotyped behavior, locomotor activity and general behavioral reactivity in monkeys fed n-3 fatty acid deficient diets compared to monkeys fed
-linolenic acid. Another physiological finding from the n-3 fatty acid deficient monkey, polydipsia accompanied by polyuria in the absence of abnormal renal function [48], could also be a manifestation of reactivity or impulsivity according to speculation by Neuringer and Reisbick. On the other hand, the DHA status of monkeys has not influenced performance on several kinds of learning tasks in monkey infants or adults [46], evidence against a primary effect of lower neural DHA accumulation on cognition. A methodological advance in measurement of infant cognition involves the measurement of look duration in conjunction with heart-rate measures. The availability of heart-rate information during exposure to visual stimuli permits looking to be parsed into three distinct phases. ‘Orientation’ reflects a simple reaction to detection of the stimulus. ‘Sustained attention’ includes the initial deceleration of heart rate and is presumed to reflect the maintenance of attention to the stimulus. During the final phase, ‘attention termination’, heart rate begins to increase reflecting the end of processing [49]. There is evidence that at least some infants with longer visual fixations spend more time in ‘attention termination’ rather than in ‘active processing’ [50]. A study is underway to determine if infant LCPUFA status is related to one or more of these phases of attention (Colombo J, Carlson SE, in progress). Performance on a problem-solving task was enhanced in human infants fed formulas with DHA and AA compared to formulas without them [51,52]. The findings could be due to higher cognitive ability, but in the absence of data for

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other kinds of behavioral domains, it is not possible to conclude that the effects observed were due to differences in learning ability per se. In contrast to the non-human primate, human infant studies have not measured behaviors reflective of reactivity or impulsivity in relation to DHA status.

Essential fatty acid deficiency vs conditional deficiency of DHA or AA Linoleic acid and
-linolenic acid are essential nutrients. Part of their essentiality is related to the physiological need for the products of these fatty acids, AA and DHA, respectively. Biosynthesis of DHA from
-linolenic acid may not permit human infants to accumulate sufficient DHA for optimal function. In other words, DHA might be a ‘conditionally essential nutrient’ for some human infants. To be considered conditionally essential a product of an essential nutrient must confer some functional benefit in the presence of the essential nutrient in the diet [53]. Because of their rapid growth, human infants are more likely than other healthy individuals to have a ‘conditional’ need for the metabolic products of essential nutrients. The non-human primate studies have used n-3 fatty acid deficiency as the model to study the effects of changes in retinal and brain DHA and the effects of these changes on visual development and other types of behavior. Human infants cannot knowingly be fed diets deficient in any essential nutrient and
-linolenic acid is no exception. In the human studies, diets with
-linolenic acid have been fed with or without DHA. Behaviors analogous to those affected by lower retinal and brain DHA accumulation in monkeys have been studied to determine if DHA improves specific visual or other developmental functions, i.e. if DHA is a conditionally essential nutrient for human infants. There are several potential reasons to suggest that DHA might be a conditionally essential nutrient for some infants. Several studies have shown that preterm infants convert essential fatty acids to DHA and AA [9–12], however, there are at least three reasons why synthesis might be inadequate. First individual rates of synthesis among infants are quite variable [10]. Second, if energy intake is inadequate, as frequently occurs in preterm infants in the first weeks of life, the essential fatty acids

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may be preferentially oxidized for energy rather than converted to DHA or AA [54–56]. Third, needs for the product may exceed ability to synthesize even when synthetic rates are high. The latter may be influenced by the physiological state of maturity. For example, birth before term and poor intrauterine growth due to other causes can reduce the brain accumulation of DHA and AA during intrauterine life [4], when there is active transport from mother to fetus [6]. Similarly, maternal DHA status may influence infant DHA accumulation. Maternal DHA status is known to be quite variable both within [57] and among cultural groups [58], and maternal DHA status has been shown to be related to infant status [57,59]. Infant DHA status at birth, in turn, is correlated with infant DHA and AA status later in infancy [60].

Evidence of underlying variability in DHA status of human infants and the possible role of maternal status The variability of DHA accumulation in human brain [4] and cord blood at birth [57,59] can be taken as evidence that maternal factors influence the amount of LCPUFA transferred to the infant. One of these factors is maternal DHA intake. Harris et al. [61] showed that maternal DHA intake can increase the amount of DHA transferred to infants. Infants of women who consume DHA during pregnancy [62] or lactation [63] have higher erythrocyte phospholipid DHA compared to infants of women who breast fed without DHA supplementation. Arbuckle and Innis [64] fed fish oil as a source of DHA and increased sow milk DHA and accumulation of DHA in erythrocytes, plasma, liver and brain (but not the retina) of the suckling piglet. Nevertheless, we have noted a large variation in plasma lipid DHA in a group of pregnant women who consumed very little DHA [57] and among infants who consumed the identical formula for many months [65]. Such data indicate that there could be underlying genetic differences, i.e. in DHA biosynthesis, that influence maternal and infant LCPUFA status. As noted before, and consistent with this theory, infants have quite variable amounts of DHA synthesis, and not all appeared to synthesize DHA when studied short term [10].

DHA and AA in infant development

Pregnancy itself leads to an increase of approximately 50% in maternal plasma phospholipid DHA above nonpregnant levels [58,66]. Interestingly, this relative increase is quite similar in all populations that have been studied even though the difference in DHA status among populations is quite large, presumably reflecting the cultural pattern of food intake and possibly other factors [58].

Descriptive studies of infant DHA and AA status Two early descriptive studies suggested that DHA and AA status of infants fed infant formula might be lower than that of infants fed human milk. Sanders and Naismith [7] first reported that term infants fed formulas compared with human milk had lower erythrocyte phospholipid DHA and AA, however, the significance of the observation was not apparent. Several years later we made the same observation by chance while comparing the effect of formulas with very different amounts of linoleic acid and
-linolenic acid on erythrocyte LCPUFA composition of term infants [8]. Only small differences were found in red blood cell phospholipid LCPUFA of infants fed the two formulas, but the infants fed human milk had significantly higher levels of these fatty acid in their red blood cell phospholipids, especially DHA. During the past 20 years, many studies have measured LCPUFA in red blood cell and plasma lipids as a marker for the effects of diet on brain DHA accumulation. Without exception, infants fed DHA, whether fed human milk or formulas containing DHA, have been found to have higher amounts of circulating DHA than infants not fed DHA while on the diet studied. Moreover, as noted previously, studies at autopsy confirm that DHA and AA in the diet are associated with higher brain DHA and higher DHA and AA in adipose tissue, liver, and skeletal muscle of breast-fed compared to formula-fed infants [16–19]. Nevertheless, such studies are not evidence of infant need for DHA. Only functional studies of randomized groups can address this question adequately. About the time that the first descriptive studies were published, Clandinin et al. [3] reported that brain DHA accumulated rapidly in the last intrauterine trimester, studies in animals indicated that low brain DHA accumulation influenced various behaviours, i.e. brain functions [21]. Early work

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with n-3 fatty acid deficient non-human primates showed that the visual system was affected by low DHA accumulation in retina and brain. Together these reports made it plausible to suggest that infants fed formula, especially very preterm infants, might not accumulate enough retinal and brain DHA for optimal visual development. To test the theory that DHA was a conditionally essential nutrient for infants, randomized studies of groups of infants were fed formulas with and without DHA. During the past 15 years, a number of such studies have been completed. The studies have focused mainly on visual function and to a lesser degree on other aspects of development. The first studies were of preterm infants. Preliminary results suggested this theory was correct [67,68], and others began to study term infants. The first studies in preterm and term infants showed higher visual function at some age during infancy in infants provided with DHA [36,37,68–70]. Retinal DHA was not affected by dietary DHA in the one study that measured retinal DHA at autopsy of infants fed human milk or formula [18]. The evidence suggests preferential and optimal incorporation of DHA by the retina even in situations when DHA availability is low. Another line of evidence could be used to suggest the same thing: Preterm infants fed an
-linolenic aciddeficient formula initially had abnormal electroretinogram responses compared to those fed
-linolenic acid-containing formula or human milk, however, their responses became normal shortly after expected term age [68,69]. The retina may accumulate DHA preferentially under circumstances when DHA is not sufficient to accumulate normally in the brain. These data suggest that the effects on visual development observed in what are now a number of randomized studies of formulas with and without DHA are most likely the result of changes in brain (central) vision rather than to higher DHA in the retina. Infants fed experimental formulas with DHA from a variety of sources, have been found to have increases in plasma and red blood cell lipid DHA. There are not any studies that have confirmed these levels are related to higher DHA in any tissue, but this assumption is basic to the randomized trials and supported by animal work [71]. After DHA is removed from the diet in infancy, erythrocyte DHA declines over a period of 7 months [65]. It cannot be assumed that plasma and red blood cell DHA reflects brain DHA in this or any other situation. Once DHA has accumulated in the

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brain, it is generally accepted that it is quite resistant to change. Red blood cell and plasma DHA have been used to infer DHA status in some groups of children and adults, but it is not clear how or if blood levels of DHA are related to DHA in brain or any other tissues. The first randomized studies assumed that formulas to which DHA was added contained sufficient
-linolenic acid so as not to limit DHA formation. What amount of
-linolenic acid would this be? Animal studies conducted by Innis and coworkers [71] suggested that at least 1% of energy from
-linolenic acid could result in normal brain DHA accumulation. While the optimal amount of
-linolenic acid in the diet of human infants has not been determined, the animal work could be used to suggest that aim, less than 1% of energy might represent some degree of essential fatty acid deficiency. In 1986, when the first studies were begun, not all formulas in the world contained 1% of energy from
-linolenic acid. While one randomized study in the US included a group fed a low
-linolenic acid formula as well as a group fed a good level of
-linolenic acid [68,69], formulas in Europe typically contained less than 1% of energy from
-linolenic acid. Consequently, formulas containing DHA were commonly compared with formulas that could now be considered to be limited in the essential n-3 fatty acid. Such comparisons can validate the importance of higher DHA stuatus for visual and other aspects of development. They cannot prove that DHA is a conditionally essential nutrient in the way they could if DHA were fed with sufficient dietary
-linolenic acid. There are significant cost implications for concluding that DHA should be fed in addition to
-linolenic acid. The
-linolenic acid content of formulas can be altered without clinical studies and regulatory approval, and
-linolenic acid is a less expensive commodity that DHA.

Randomized clinical studies to compare formulas with and without DHA Randomized studies in human infants have asked if synthesis was adequate for infants born early or fed artificial milks without DHA and AA. With a couple of exceptions, randomization has occurred after parents chose to feed formula and the infants

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were then assigned to formulas with and without DHA and with varying amounts of EPA (0 to 0.3% of total fatty acids) or AA (0 to 0.6% of total fatty acids). Randomized studies have included groups of very low birth weight infants (<1500 g at birth) and term infants fed formulas with and without DHA. DHA in the experimental formulas has come from fish oils with relatively more or less eicosapentaenoic acid (EPA, 20:5n-3), egg phospholipids, and algae. DHA has been fed with AA, either from food sources that include both DHA and AA such as egg phospholipids or fungal oils. All sources of DHA have been shown to increase blood lipid levels of DHA. Formulas with AA have been shown to prevent the declines in AA in circulating lipids [42,72] that result from feeding n-3 LCPUFA without AA [72].

Infant growth and DHA There is evidence that some preterm infants might have a conditional need for AA as well as DHA [73], and feeding DHA [73] may exacerbate the need. Three of the four studies that fed a source of n-3 LCPUFA without AA reported lower growth in the first year of life. The effects on growth included lower weight, length and head circumference [74], lower weight-for-length [37] and lower growth only in males [75]. However, two of the three studies measured developmental outcomes and found higher visual acuity in the first half of infancy [36,37], more mature attentional development late in infancy [38,39] and one found higher performance on a scale of development, the Bayley Mental Developmental Index, at 12 months corrected age [53]. Consequently, the growth effects did not appear to be of significance for development. A recent review of growth in all of the clinical studies that have been published makes it clear that few of the studies have had good power to detect anything but a very large difference in growth [76]. Several recently published large trials have not found lower growth among term [77–80] or preterm [42,81–83] infants when DHA in experimental formulas contained both DHA and AA. Two studies, found more rapid weight gain in term and preterm infants fed a formula with DHA and AA respectively [80,81] and two found somewhat lower mean increases in length during some or all

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of infancy in one or more groups fed a source of DHA and AA after preterm birth [81–83]. Infant development and DHA The effects of interventions with polyunsaturated fatty acid in randomized trials on clinical outcomes and on visual and neural development have been discussed and summarized in several recent reviews [84–87] and will not be discussed individually here. In general, DHA has been shown to benefit visual development for preterm infants. Among term infants, higher DHA intakes have been more likely to show benefits than lower intakes, although there are exceptions. These exceptions could be the result of methodological differences among studies as well as the amount of DHA consumed in the formula. Approximately 13 randomized studies in preterm infants and 19 studies in term infants have measured some physiological response, often only growth. Not all had sufficient statistical power to detect anything but very large effects on the physiological outcomes posed by the study. An evaluation of the validity of the studies needs to be taken into account particularly for studies that found no effect. The large trials are not exempt from concerns about adequate power, because some of these trials included many testers for tests that involve some level of subjectivity. Trials in term infants have been conducted without an understanding of variables that were influential for DHA status, and, therefore, without controlling for these variables [88]. Two systematic reviews published last year are now somewhat dated, however, studies published in the past year have confirmed previous reports for term and preterm infants so it is unlikely that the authors of these reviews would reach different conclusions today. Both reviews concluded that preterm infants benefit from receiving dietary DHA, at least in infancy [89,90]. Most of the studies have focused on the first 12 months of life. One systematic review also concluded that there appeared to be benefits for term infants in the short term [91], whereas another did not reach this conclusion [92]. Valid studies of function may also employ infants who have been fed human milk with different amounts of DHA. There are two such studies reported in the literature, in which women who planned to feed human milk consumed an

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algal source of DHA during lactation [63,93]. Neither study showed any effect on early visual or cognitive development of DHA intake above that typically received by term US infants fed human milk after birth [63,93]. However, it has been reported recently that at 30 months of age, infants in one of the studies [94] demonstrated a significant increase in performance on the scale of Bayley Psychomotor Development (PDI), a test which emphasizes fine motor development [95]. Several points above the existing literature on LCPUFA and infant development should be emphasized. Firstly, only a few of the possible developmental outcomes affected by DHA status have been studied in randomized trials comparing formulas or human milk differing in DHA content. Secondly, the studies that have been done have focused mainly on development in the first 12 to 18 months post-term. Thirdly, we currently have little understanding of the measures of development that should be measured after infancy even though development during the early months could impact later stages of development. Jensen et al. [93,94] suggests that ‘no effect’ outcomes in the early months cannot be used to conclude that there are not effects later on. Finally, we know very little about the amount of DHA that is optimal for development, and there is now at least limited evidence that the low amounts in human milk of women in North America might not be optimal for development of term infants.

New animal studies of potential LCPUFA mechanisms Animal studies generated the first evidence that DHA accumulation in the central nervous system influenced visual function and early development. Now that a large number of studies have found visual and other behaviors to be influenced by feeding DHA to infants, some investigations have returned to animal models and model systems in an attempt to understand how lower brain DHA influences animal and human behavior. Chalon and coworkers have produced a considerable body of work on the effects of
-linolenic acid deficiency on monoaminergic transmission [96,97]. Collectively, these studies have shown a lower pool of dopamine in pre-synaptic vessels in both the meso-cortical and meso-limbic systems when DHA is replaced by DPA. The meso-cortical

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system seems to be hypofunctional due to lower basal release of dopamine and less dopamine D2 receptors, whereas the mesolimbic system seems to be hyperfunction with increased basal release of dopamine and increased levels of dopamine D2 receptors [98]. Changes in the dopaminergic system of the meso-cortical and meso-limbic systems can be related to some of the behavioral changes that have been observed in animals of n-3 fatty acid deficiency. Reisbick and Neuringer [99] have proposed that the low performance on cognitive tasks in n-3 PUFA deficient animals might be due to increased reactivity to reward related to dopaminergic function of the nucleus accumbens. Changes in attention, motivation or reactivity rather than a primary effect on cognitive behavior could be related to observations of lower problem solving ability in human infants with lower relative to higher DHA status [51,52], as noted previously. Dopaminergic systems interact with other neurotransmitter systems such as serotonergic, glutamatergic, GABAergic and cholinergic, which influence behavior [98]. Innis et al. [100] have increases in dopamine, serotonin and their metabolites when DHA and AA are added to piglet feeds compared to a diet deficient in
-linolenic acid. In a later study, they found newborn brain dopamine to be inversely related to DHA in brain phospholipids DHA but negatively related to AA, which were in turn related to the amount of
-linolenic acid in the diet [101]. DHA status has also been shown to reduce the GABA response [102] and to increase acetylcholine [103]. Other biochemical changes in the brain influenced by DHA and AA nutrition could also influence behavior. Acylethanolamides are nonoxidative metabolites of LCPUFA that act as endogenous agonists at the brain cannaboinoid receptor [104]. Both low and high doses of injected anandamide (arachidonoylethanolamide) have been shown to have physiological effects in animals. Anandamide has effects on intestinal motility [105], sleep, wakefulness and memory consolidation [106], and can buffer dopamine overproduction [107]. Piglets fed diets with DHA and AA have large increases of several biologically active acylethanolamide metabolites of these two fatty acids [108]. Dietary AA did not increase brain AA, but it did result in large increases in brain anandamide [108]. It is reasonable to speculate that these changes in acylethanolamides of the n-3 and

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n-6 fatty acids, or a change in their balance, could affect behavior. When DPA (22:5n-6) replaces DHA, as has been shown to occur in
-linolenic acid deficiency [22–26], the molecular species of phospholipids in membranes are changed [109] and these lead to changes in biophysical properties of the membranes [110]. These changes could result in many other effects including the changes in neurotransmitters and their receptors noted by Chalon and others. Higher levels of membrane DHA have also been associated with decreased apoptosis in both the retina [111] and in cell systems [112]. However, both apoptotoic and antiapoptotic functions of DHA have been reported, and some of the findings appear to be artifactual [110]. Salem et al. [110] note that ‘it is likely that the apoptotic effect of DHA is the result of multiple regulations at various signaling stages, ranging from the plasma membrane to nuclear events, most of which have yet to be discovered.’ It is already known that DHA affects transcription through nuclear hormone receptors such as the peroxisomal proliferator-activated receptor [113,114]. Preliminary screens of brain mRNA from rats fed an
-linolenic acid deficient diet from the beginning of life through weaning suggest that numerous genes involved in signal transduction are downregulated by reductions in brain DHA accumulation and replacement with DPA (22:5n-6) [115]. Readers interested in state-of-the-art discussion of the mechanisms of action that could underlie low DHA status in the central nervous system and retina, respectively, are referred to reviews by Salem et al. [110] and Politi [116]. At this time, it appears that there may be a variety of effects in the central nervous system that could account for the changes in visual function and behavior that have been reported with low DHA status in animal models and human clinical trials.

Summary Systematic reviews of the randomized studies of infants fed formulas with and without DHA have concluded that visual development of preterm infants benefits from dietary DHA in infancy [89,90]. One systematic review also concluded that there appeared to be benefits for first year visual development of term infants [91], whereas another did not reach this conclusion [92]. DHA and AA

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have been added to some formulas in Europe, Asia and South America during the past 10 years, and a recent FDA decision makes it likely that they will be added to formulas in North America by 2002. Many of the principal investigators involved in the published trials of DHA supplementation participated in a workshop that concluded term infant formulas should contain at least 0.2% of total fatty acids as DHA and 0.35% as AA [117]. Recommendations for AA and DHA were higher for pre-term infants, 0.4 and 0.35% of total fatty acids, respectively, because preterm infants are born with much less total body DHA and AA. The report indicates that breast milk is the preferred feeding for all healthy infants and that is supplies preformed DHA and AA. It remains to be seen how much DHA and AA will be included in formulas in the US. Reports of mean AA and DHA in human milk from different cultures demonstrates that among cultures, there is at most a 2- to 3-fold difference in AA concentration of milk but at least a 13-fold difference in DHA concentration [118,119]. While the addition of LCPUFA to infant formula may soon make it impossible to study infants on diets without DHA. Given the expense of the various sources of DHA and AA, it is not inconceivable that amounts on the low end of the range will be added. If so, randomized studies could still be done to define the optimal amount of DHA that should be fed. The same studies could allow for investigations of other physiological functions that have been not been studied under circumstances of varied DHA and AA status and that are still very much needed. Clinical investigations could also be of benefit (1) to learn the factors that influence DHA and AA status of infants before birth, and (2) to determine the optimal DHA and AA status before birth. Animal studies are needed to determine (1) the mechanisms by which changes in the status of these LCPUFA during development influence physiological functions of all kinds, and (2) if these functions are programmed to any degree by LCPUFA status. Finally, a very important question that has not been answered as if the effects of low DHA status during development can be reversed and, if so, when and how. References 1 Svennerholm J. Distribution and fatty acid composition of phosphoglycerides in normal human brain. J Lipid Res 1968; 9: 570–579.

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2 Anderson RE, Maude MB, Zimmerman W. Lipids of ocular tissues. X. Lipid composition of subcellular fractions of bovine retina. Vision Res 1975; 15: 1087–1090. 3 Martin RE, Bazan NG. Changing fatty acid content of growth cone lipids prior to synaptogenesis. J Neurochem 1992; 59: 318–325. 4 Clandinin MT, Chappell JE, Leong S, Heim T, Swyer PR, Chance GW. Intrauterine fatty acid accretion rates in human brain: Implications for fatty acid requirements. Early Hum Dev 1980; 4: 121–129. 5 Martinez M. Developmental profiles of polyunsaturated fatty acids in the brain of normal infants and patients with peroxisomal diseases: severe deficiency of docosahexaenoic acid in Zellweger’s and Pseudo-Zellweger’s Syndromes. In: Simopoulos AP, Kifer RR, Martin RE, Marlow SM (eds) Health Effects of 3 Polyunsaturated Fatty Acids in Seafood, World Rev Nutr Diet, Vol. 66. Basel: Karger, 1991; 87–102. 6 Dutta-Roy AK. Transport mechanisms for long-chain polyunsaturated fatty acids in the human placenta. Am J Clin Nutr 2000; 71: 315S–322S. 7 Sanders TAB, Naismith DJ. A comparison of the influence of breast-feeding and bottle-feeding on the fatty acid composition of erythrocytes. Br J Nutr 1979; 41: 619–623. 8 Putnam JC, Carlson SE, DeVoe PW, Barness LA. The effect of variations in dietary fatty acids on the fatty acid composition of erythrocyte phosphatidylcholine and phosphatidylethanolamine in human infants. Am J Clin Nutr 1982; 36: 106–114. 9 Sauerwald TU, Jensen CL, Chen H, Anderson RE, Heird WC, Hachey DL. Effect of dietary 18:-3 intake and postnatal age on the kinetics of elongation and desaturation of 18:-6 and 18:-3. Pediatr Res 1995; 37: 319A. 10 Carnielli VP, Wattimena DJ, Luijendijk IH, Boerlage A, Degenhart HJ, Sauer PJ. The very low birth weight premature infant is capable of synthesizing arachidonic and docosahexaenoic acids from linoleic and linolenic acids. Pediatr Res 1996; 40: 169–174. 11 Salem N Jr, Wegher B, Mena P, Uauy R. Arachidonic and docosahexaenoic acids are biosynthesized from their 18-carbon precursors in human infants. Proc Natl Acad Sci USA 1996; 93: 49–54. 12 Sauerwald TU, Hachey DL, Jensen CL, Chen H, Anderson RE, Heird WC. Intermediates in endogenous synthesis of C22:6 omega 3 and C20:4 omega 6 by term and pre-term infants. Pediatr Res 1997; 41: 183– 187. 13 Carlson SE, Rhodes PG, Ferguson MG. Docosahexaenoic acid status of preterm infants at birth and following feeding with human milk or formula. Am J Clin Nutr 1986; 44: 798–804. 14 Carlson SE, Rhodes PG, Rao V, Goldgar DE. Effect of fish oil supplementation on the omega-3 fatty acid content of red blood cell membranes in pre-term infants. Pediatr Res 1987; 21: 507–510. 15 Liu C-CF, Carlson SE, Rhodes PG, Rao V, Meydrech EF. Increase in plasma phospholipid docosahexaenoic acid and eicosapentaenoic acids as a reflection of their intake and mode of administration. Pediatr Res 1987; 22: 292– 296.

446

16 Farquharson J, Cockburn F, Patrick WA, Jamieson EC, Logan RW. Infant cerebral cortex phospholipid fatty-acid composition and diet. Lancet 1992; 340: 810– 813. 17 Farquharson J, Cockburn F, Patrick WA, Jamieson EC, Logan RW. Effect of diet on infant subcutaneous tissue triglyceride fatty acids. Arch Dis Child 1993; 69: 589– 593. 18 Makrides M, Neumann MA, Byard RW, Simmer K, Gibson RA. Fatty acid composition of brain, retina, and erythrocytes in breast- and formula-fed infants. Am J Clin Nutr 1994; 60: 189–194. 19 Farquharson J, Cockburn F, Patrick WA, Howatson AG, Cockburn F. Age- and dietary-related distributions of hepatic arachidonic and docosahexaenoic acid in early infancy. Pediatr Res 1995; 38: 361–365. 20 Holman RT. Essential fatty acid deficiency. Prog Chem Fats and Other Lipids 1968; 9: 258–348. 21 Wainwright PE. Lipids and behavior: the evidence from animal models. In: Dobbing J (ed.) Lipids, Learning and the Brain: Fats in Infant Formulas, Report of the 103rd Ross Conference on Pediatric Research. Columbus, OH: Ross Laboratories, 1993; 69–101. 22 Galli C, Trzeciak HI, Paoletti R. Effects of dietary fatty acids on the fatty acid composition of brain ethanolamine phosphoglyceride: Reciprocal replacement of n-6 and n-3 polyunsaturated fatty acids. Biochim Biophys Acta 1971; 248: 449–454. 23 Neuringer M, Connor WE, Lin DS, Barstad L, Luck S. Biochemical and functional effects of prenatal and postnatal omega-3 fatty acid deficiency on retina and brain in rhesus monkeys. Proc Natl Acad Sci USA 1986; 83: 4021–4025. 24 Carlson SE, Carver JD, House SG. High fat diets varying in ratios of polyunsaturated to saturated fat and linolenic acid: A comparison of rat neural and red cell membrane phospholipids. J Nutr 1986; 116: 718–725. 25 Yamamoto N, Saitoh M, Moriuchi A, Nomura M, Okuyama H. Effect of dietary
-linolenate/linoleate balance on lipid compositions and learning ability in rats. J Lipid Res 1987; 28: 144–151. 26 Bourre JM, Francois M, Youyou A, Dumont O, Piciotti M, Pascal G, Durand G. The effects of dietary alphalinolenic acid on the composition of nerve membranes, enzymatic activity, amplitude of electrophysiological parameters, resistance to poisons and performance of learning tasks in rats. J Nutr 1989; 119: 1880–1892. 27 Carlson SE, Neuringer M. Polyunsaturated fatty acid status and neurodevelopment: A summary and critical analysis of the literature. Lipids 1999; 34: 171–178. 28 Sinclair AJ, Crawford MA. The accumulation of arachidonate and docosahexaenoate in the developing rat brain. J Neurochem 1972; 19: 1753. 29 Dobbing J. Comparative aspects of the brain growth spurt. Early Hum Dev 1979; 3: 79083. 30 Neuringer M, Connor WE, Van Petten C, Barstad L. Dietary omega-3 fatty acid deficiency and visual loss in infant rhesus monkeys. J Clin Invest 1984; 73: 272–276. 31 Neuringer M. The relationship of fatty acid composition to function in the retina and visual system. In: Dobbing J (ed.) Lipids, Learning and the Brain: Fats in Infant Formulas. Columbus, OH: Ross Laboratories, 134–158.

S. E. Carlson

32 Neuringer M, Connor WE, Barstad L, Lin D. Supplementation with docosahexaenoic acid (22:63) fails to correct electroretinogram abnormalities produced by omega-3 fatty acid deficiency in rhesus monkeys. Invest Ophthalmol Vis Sci 1990; 31: 426 (abstract). 33 Neuringer M, Connor WE, Lin DS, Anderson GJ. Effects of n-3 fatty acid deficiency on retinal physiology and visual function. In: Sinclair AJ, Gibson RA (eds) Proceedings of the Third International Congress on Essential Fatty Acids and Eicosanoids. Champaign, IL: American Oil Chemists’ Society, 161–164. 34 Reisbick S, Neuringer M, Gohl E, Wald R, Anderson GJ. Visual attention in infant monkeys: Effects of dietary fatty acids and age. Devel Psych 1997; 33: 387–395. 35 Neuringer M, Reisbick S, Teemer C. Relationships between visual acuity and visual attention measures in rhesus monkey infants. Invest Ophthalmol Vis Sci 1996; 37: S532 (abstract). 36 Carlson SE, Werkman SH, Rhodes PG, Tolley EA. Visual acuity development in healthy pre-term infants. Effect of marine oil supplementation. Am J Clin Nutr 1993; 58: 35–42. 37 Carlson SE, Werkman SH, Tolley EA. The effect of long chain n-3 fatty acid supplementation on visual acuity and growth of pre-term infants with and without bronchopulmonary dysplasia. Am J Clin Nutr 1996; 63: 687–697. 38 Werkman SH, Carlson SE. A randomized trial of visual attention of pre-term infants fed docosahexaenoic acid until 9 months. Lipids 1996; 31: 91–97. 39 Carlson SE, Werkman SH. A randomized trial of visual attention of pre-term infants fed docosahexaenoic acid until 2 months. Lipids 1996; 31: 85–90. 40 Carlson SE. Early visual acuity does not correlate with later evidence of visual processing in pre-term infants although each is improved by the addition of docosahexaenoic acid to infant formula. Second International Congress of the International Society for the Study of Fatty Acids and Lipids, Bethesda, MD, June 1995 (abstract). 41 Jacobson SW. Assessment of long-chain polyunsaturated fatty acid nutritional supplementation on infant neurobehavioral development and visual acuity. Lipids 1999; 34: 151–160. 42 O’Connor DL, Hall R, Adamkin D, Auestad N, Castillo M, Connor WE, Connor SL, Fitzgerald K, GrohWargo S, Harmann EE, Jacobs J, Janowsky J, Lucas A, Margeson D, Mena P, Neuringer M, Nesin M, Singer L, Stephenson T, Szabo J, Zemon V. Growth and development in pre-term infants fed long-chain polyunsaturated fatty acids: A prospective, randomized controlled trial. Pediatr 2001; 108: 359–371. 43 Colombo J, Mitchell DW. Individual differences in early visual attention: Fixation time and information processing. In: Colombo J, Fagan J (eds) Individual Differences in Infancy: Reliability, Stability and Prediction. Hillsdale, NJ: Erlbaum, 193–227. 44 Colombo J, Mitchell DW, Coldren JT, Freeseman LJ. Individual differences in infant visual attention: Are short lookers faster processors or feature processors? Child Devel 1991; 62: 1247–1257.

DHA and AA in infant development

45 Johnson MH, Posner MI, Rothbart MK. Components of visual orienting in early infancy: Contingency learning, anticipatory looking and disengaging. J Cog Neurosci 1991; 3: 335–344. 46 Reisbick S, Neuringer M, Connor WE. Effect of n-3 fatty acid deficiency in nonhuman primates. In: Bindels JG, Goedhart AC, Visser HKA (eds) Recent Developments in Infant Nutrition. Dordrecht: Kluwer Academic Publishers, 157–172. 47 Reisbick S, Neuringer M, Hasnain R, Connor WE. Home cage behavior of rhesus monkeys with long-term deficiency of omega-3 fatty acids. Physiol Behav 1994; 55: 231–239. 48 Reisbick S, Neuringer M, Connor WE, Barstad L. Postnatal deficiency of omega-3 fatty acids in monkeys: Fluid intake and urine concentration. Physiol Behav 1992; 51: 473–479. 49 Colombo J. Recent advances in infant cognition: Implications for LC-PUFA supplementation studies. Lipids 2001; 36: 919–926. 50 Colombo J, Frick JE, Gorman SH, Caebolt K. Heart rate patterns during infant controlled habituation sessions. Washington, DC: Society for Research in Child Development, 1997. 51 Willatts P, Forsyth JS, DiModugno MK, Varma S, Colvin M. Effect of long-chain polyunsaturated fatty acids in infant formula on problem solving at 10 month of age. Lancet 1998; 352: 688–691. 52 Willats P, Forsyth JS, DiModugno MK, Varma S, Colvin M. Influence of long-chain polyunsaturated fatty acids on infant cognitive function. Lipids 1998; 33: 973–980. 53 Carlson SE. Long-chain polyunsaturated fatty acid supplementation of pre-term infants. In: Dobbing J (ed.) Developing Brain and Behavior: The Role of Lipids in Infant Formula. London: Academic Press Limited, 1997; 41–78. 54 Clouet P, Niot I, Bezard J. Pathway of alpha-linolenic acid through the mitochondrial outer membrane in the rat liver and influence on the rate of oxidation. Comparison with linoleic and oleic acids. Biochem J 1989; 263: 867–873. 55 Ide T, Murata M, Sugano M. Stimulation of the activities of hepatic fatty acid oxidation enzymes by dietary fat rich in alpha-linolenic acid in rats. J Lipid Res 1996; 37: 448–463. 56 Perichon R, Bourre JM. Peroxisomal beta-oxidation and catalase activity during development and aging in mouse liver. Biochimie 1995; 77: 288–293. 57 Carlson SE, Huang M, Smuts M, Mundy D, Plasse T, Major S. A randomized clinical trial of docosahexaenoic acid supplementation during the third trimester of pregnancy and pregnancy outcome. ISSIAL abstracts (in press). 58 Otto SJ, van Houwelingen AC, Antal M, Manninen A, Godfrey K, Lopez-Jaramillo P, Hornstra G. Maternal and neonatal essential fatty acid status in phospholipids: An international comparative study. Eur J Clin Nutr 1997; 51: 232–242. 59 Al MD, van Houwelingen AC, Kester AD, Hasaart TH, deJong AE, Hornstra G. Maternal essential fatty acid patterns during normal pregnancy and their relationship to the neonatal essential fatty acid status. Br J Nutr 1995; 74: 55–68.

447

60 Guesnet P, Pugo-Gunsam P, Maurage C, Pinault M, Giraudeau B, Alessandri J-M, Durand G, Antoine J-M, Couet C. Blood lipid concentrations of docosahexaenoic acid and arachidonic acid at birth determine their relative postnatal changes in term infants fed breast milk or formula. Am J Clin Nutr 1999; 70: 292–280. 61 Harris WS, Connor WE, Lindsey S. Will dietary omega-3 fatty acids change the composition of human milk? Am J Clin Nutr 1984; 40: 780–785. 62 Connor WE, Lowewnsohn R, Hatcher L. Increased docosahexaenoic acid levels in human newborn infants by administration of sardines and fish oil during pregnancy. Lipids 1996; 31: S183. 63 Gibson RA, Neumann MA, Makrides M. Effect of increasing breast milk docosahexaenoic acid on plasma and erythrocyte phospholipid fatty acids and neural indices of exclusively breast fed infants. Eur J Clin Nutr 1997; 51: 578–584. 64 Arbuckle LD, Innis SM. Docosahexaenoic acid is transferred through maternal diet to milk and to tissues of natural milk-fed piglets. J Nutr 1993; 123: 1668– 1675. 65 Carlson SE, Cooke RJ, Rhodes PG, Peeples JM, Werkman SH. Effect of vegetable and marine oils in pre-term infant formulas on blood arachidonic and docosahexaenoic acids. J Pediatr 1992; 120: S159–S167. 66 Otto SJ, van Houwelingen AC, Badart-Smook A, Hornstra G. Changes in the maternal essential fatty acid profile during early pregnancy and the relation of the profile to diet. Am J Clin Nutr 2001; 73: 302–307. 67 Carlson S, Cooke R, Werkman S, Peeples J. Docosahexaenoate (DHA) and eicosapentaenoate (EPA) supplementation of pre-term (PT) infants: Effects on phospholipid DHA and visual acuity. FASEB J 1989; 3: A1056. 68 Uauy RD, Birch DG, Birch EE, Tyson JE, Hoffman DR. Effect of dietary omega-3 fatty acids on retinal function of very-low-birth-weight neonates. Pediatr Res 1990; 28: 485–492. 69 Birch DG, Birch EE, Hoffman DR, Uauy RD. Retinal development in very low birth weight infants fed diets differing in omega-3 fatty acids. Phthalmol Vis Sci 1992; 650–676. 70 Makrides M, Neumann M, Simmer K, Pater J, Gibson R. Are long-chain polyunsaturated fatty acids essential nutrients in infancy? Lancet 1995; 345: 1463–1468. 71 Arbuckle LD, Innis SM. Docosahexaenoic acid in developing brain and retina of piglets fed high or low alpha-linolenate formula with and without fish oil. Lipids 1992; 27: 89–93. 72 Carlson SE. Arachidonic acid status of human infants: Influences of gestational age at birth and diets with very long chain n-3 and n-6 fatty acids. J Nutr 1996; 126: 1092S–1098S. 73 Carlson SE, Werkman SH, Peeples JM, Cooke RJ, Tolley EA. Arachidonic acid status correlates with first year growth in pre-term infants. Proc Natl Acad Sci USA 1993; 90: 1073–1077. 74 Carlson SE, Cooke RJ, Werkman SH, Tolley EA. First year growth of pre-term infants fed standard compared to marine oil n-3 supplemented formula. Lipids 1992; 27: 901–907.

448

75 Ryan AS, Montalto MB, Groh-Wargo S, Mimouni F, Sentipal-Walerius J, Doyle J, et al. Effect of DHAcontaining formula on growth of pre-term infants to 59 weeks postmenstrual age. Am J Hum Biol 1999; 11: 457–467. 76 Lapillone A, Carlson SE. Polyunsaturated fatty acids and infant growth. Lipids 2001; 36: 901–912. 77 Auestad N, Montalto MB, Hall RT, Fitzgerald KM, Wheeler RE, Connor WE, et al. Visual acuity, erythrocyte fatty acid composition, and growth in term infants fed formulas with long chain polyunsaturated fatty acids for one year. Ross Pediatric Lipid Study. Pediatr Res 1997; 41: 1–10. 78 Lucas A, Stafford M, Morley R, Abbott R, Stephenson T, MacFadyen U, et al. Efficacy and safety of long-chain polyunsaturated fatty acid supplementation of infantformula milk: a randomized trial. Lancet 1999; 354: 1948–1954. 79 Auestad N, Halter R, Hall RT, Blatter M, Bogle ML, Burks W, Erickson JR, Fitzgerald KM, Dobson V, Innis SM, Singer LT, Montalto MB, Jacobs JR, Wenzi Q, Bornstein MH. Growth and development in term infants fed long-chain polyunsaturated fatty acids: A doublemasked, randomized, parallel prospective, multivariate study. Pediatrics 2001; 108: 372–381. 80 Carlson SE, Mehra S, Kagey WJ, Merkel KL, DiersenSchade DA, Harris CL, Hansen JW. Growth and development of term infants fed formulas with docosahexaenoic acid (DHA) from algal oil or fish oil and arachidonic acid from fungal oil. Pediatr Res 1999; 45: 278A. 81 Diersen-Schade DA, Hansen JW, Harris CL, Merkel KL, Wisont KD, Boettcher JA. Docosahexaenoic acid plus arachidonic acid enhance pre-term infant growth. In: Riemersma RA, Armstrona R, Kelly RW, Wilson R (eds) Essential Fatty Acids and Eicosanoids: Invited Paper from the Fourth International Congress. Barcelona, Spain: American Oil Chemists’ Society Press, 1998; 123–127. 82 Vanderhoof J, Gross S, Hegyi T, Clandinin T, Porcelli P, DeCristofaro J, et al. Evaluation of a long-chain polyunsaturated fatty acid supplemented formula on growth, tolerance, and plasma lipids in pre-term infants up to 48 weeks postconceptional age. J Pediatr Gastroenterol Nutr 1999; 29: 318–326. 83 Vanderhoof J, Gross S, Hegyi T. A multicenter longterm safety and efficacy trial of pre-term formula supplemented with long-chain polyunsaturated fatty acids. J Pediatr Gastroenterol Nutr 2000; 31: 121–127. 84 Uauy R, Hoffman DR, Periano P, Birch EE. Essential fatty acids in visual and brain development. Lipids 2001; 36: 885–896. 85 Gibson RA, Chen W, Makrides M. Randomized trials with polyunsaturated fatty acid interventions in preterm and term infants: functional and clinical outcomes. Lipids 2001; 36: 873–884. 86 Jeffrey, et al. The role of docosahexaenoic acid in retinal function. Lipids 2001; 36: 859–872. 87 Lauritzen L, Hansen HS, Jorgensen MH, Michaelsen KF. The essentiality of long chain n-3 fatty acids in relation to development and function of the brain and retina. Prog Lipid Res 2001; 40: 1–94.

S. E. Carlson

88 Tolley EA, Carlson SE. Considerations of statistical power in studies of visual development and DHA status. Invited editorial. Am J Clin Nutr 2000; 71: 1–2. 89 Simmer K. Long chain polyunsaturated fatty acid supplementation in pre-term infants. Cochrane Database System Rev 2000. 90 SanGiovanni JP, Parra-Cabrera S, Colditz GA, et al. Meta-analysis of dietary essential fatty acids and longchain polyunsaturated fatty acids as they relate to visual resolution acuity in healthy pre-term infants. Pediatrics 2000; 105: 1292–1298. 91 SanGiovanni JP, Berkeyu CS, Dwyer JTG, Colditz GA. Dietary essential fatty acids, long-chain polyunsaturated fatty acids, and visual resolution acuity in healthy fullterm infants: a systematic review. Early Hum Develop 2000; 57: 165–189. 92 Simmer K. Long chain polyunsaturated fatty acid supplementation in infants born at term. Cochrane Database Syst Rev 2000. 93 Jensen CL, Prager TC, Zou Y, Fraley JK, Maude M, Anderson RE, Heird WC. Effects of maternal docosahexaenoic acid supplementation on visual function and growth of breast-fed infants. Lipids 1999; 34: S225. 94 Jensen CL, Voigt RG, Prager TC, Zou YL, Fraley K, Rozelle J, Turich M, Liorente AM, Heird WC. Effects of maternal docosahexaenoic acid (DHA) supplementation on visual function and neurodevelopment of breast-fed infants. Pediatr Res 2001; 49: 448A. 95 Bayley N. Manual for the Bayley Scales of Infant Development. San Antonio, TX: The Psychological Corporation 1969 (2nd edn, ibid, 1993). 96 Delion S, Chalon S, Herault J, Guilloteau D, Besnard J-C, Durand G. Chronic dietary alpha-linolenic acid deficiency alters dopaminergic and serotonergic neurotransmission in rats. J Nutr 1994; 124: 2466– 2476. 97 Delion S, Chalon S, Guilloteau D, Besnard J-C, Durant G.
-Linolenic acid dietary deficiency alters age-related changes of dopaminergic and serotonergic neurotransmission in the rat frontal cortex. J Neurochem 1996; 66: 1582–1591. 98 Chalon S, Vancassel S, Zimmer L, Guilloteau D, Durand G. PUFAs and cerebral function: Focus on monoaminergic neurotransmission. Lipids 2001; 36: 937–944. 99 Reisbick S, Neuringer M. Omega-3 fatty acid deficiency and behavior: A critical review and directions for future research. In: Yehuda S, Mostofsky DI (eds) Handbook of Essential Fatty Acid Biology: Biochemistry, Physiology, and Behavioral Neurobiology. Totowa, NJ: Humana Press Inc., 397–425. 100 De la Presa-Owens S, Innis SM. Diverse, regionspecific effects of addition of arachidonic and docosahexaenoic acids to formula with low or adequate linoleic and alpha-linolenic acids on piglet brain monoaminergic neurotransmitters. Pediatr Res 2000; 48: 125–130. 101 Innis SM, de la Presa-Owens S. Dietary fatty acid in composition in pregnancy alters neurite membrane fatty acids and dopamine in newborn rat brain. J Nutr 2001; 131: 118–122.

DHA and AA in infant development

102 Hamano H, Nabekura J, Nishikawa M, Ogawa T. Docosahexaenoic acid reduces GABA response in substantia nigra neuron of rat. J Neurophysiol 1996; 75: 1264–1270. 103 Minami M, Kimura S, Endo T, Hamaue N, Hirafuji M, Togashi H, Matsumoto M, Yoshioka M, Saito H, Watanabe S, Kobayashi T, Okuyama H. Dietary docosahexaenoic acid increases cerebral acetylcholine levels and improves passive avoidance performance in strokeprone spontaneously hypertensive rats. Pharmacol Biochem Behav 1997; 58: 1123–1129. 104 Di Marzo V, Petrocellis L de, Nunzio, Sepe N, Buono A. Biosynthesis of anandamide and related acylethanolamides in mouse J774 macrophages and N18 neuroblastoma cells. Biochem J 1996; 316: 977–984. 105 Calignano A, LaRana G, Makriyannis A, Lin SY, Beltramo M, Piomelli D. Inhibition of intestinal motility by anandamide, an endogenous cannabinoid. Eur J Pharmacol 1997; 340: R7–8. 106 Murillo-Rodriquez E, Sanchez-Alavez M, Navarro L, Martinez-Gonzalez D, Drucker-Colin R, ProsperoCarcia. Anadamide modulates sleep and memory in rats. Brain Res 1998; 812: 270–274. 107 Self DW. Anandamide: A candidate neurotransmitter heads for the big leagues. Nat Neurosci 1999; 2: 303– 304. 108 Berger A, Crozier G, Bisogno T, Cavaliere P, Innis S, Di Marzo V. Anandamide and diet: Inclusion of dietary arachidonate and docosahexaenoate leads to increased brain levels of the corresponding N-acylethanolamines in piglets. Proc Natl Acad Sci USA 2001; 98: 6402– 6406. 109 Lin DS, Anderson GJ, Connor WE, Neuringer M. Effect of dietary n-3 fatty acids upon the phospholipid molecular species of the monkey retina. Invest Ophthalmol Vis Sci 1994; 35: 794–803.

449

110 Salem N, et al. Mechanisms of action of docosahexaenoic acid in the nervous system. Lipids 2001; 36: 945–960. 111 Rotstein N. Docosahexaenoic acid protects retinal photoreceptors from apoptosis induced by oxidative stress. In: PUFA in Maternal and Child Health. Am Oil Chem Soc Program and Abstracts, 2000; 38. 112 Akbar M, Kim H-Y. Docosahexaenoic acid (DHA) mediates anti-apoptotic effects through phosphatidylinositol 3-kinase pathway: A novel observation in neural apoptosis. Am Oil Chem Soc Program and Abstracts, 12. 113 Lin Q, Ruuska SE, Shaw NS, Dong D, Noy N. Ligand selectivity of the peroxisome proliferator-activator receptor alpha. Biochem 1999; 38: 185–190. 114 De Urquiza AM, Liu S, Sjoberg M, Zetterstrom RH, Griffiths W, Sjovall J, Perlmann T. Docosahexaenoic acid, a ligand for the retinoid X receptor in mouse brain. Science 2000; 290: 2140–2144. 115 Carlson SE, Gaines JB, Zhao J, Cui L, Choudhuri R, Berman NE. Effect of low brain docosahexaenoic acid on gene expression in rat frontal contex. Pediatr Res 2001; 49: 294A. 116 Politi L. Effects of docosahexaenoic acid on retinal development. Cellular and molecular aspects. Lipids 2001; 36: 927–936. 117 Koletzko B, Agostoni C, Carlson SE, Clandinin T, Hornstra G, Neuringer M, Uauy R, Yamashiro Y, Willatts P. Long chain polyunsaturated fatty acids (LCPUFA) and perinatal development. Acta Pediatr 2001; 90: 460–464. 118 Innis SM. Human milk and formula fatty acids. J Pediatr 1992; 120: S56–S61. 119 Koletzko B, Thiel I, Abiodun PO. The fatty acid composition of human milk in Europe and Africa. J Pediatr 1992; 120: S62–S70.