PHYSIOLOGICAL CONSEQUENCES OF LCPUFA DEFICIENCIES

IV. PHYSIOLOGICAL CONSEQUENCES OF LCPUFA DEFICIENCIES

Previous sections have described the biochemistry and functional roles of the essential fatty acids in the body, and it is clear from the definition that they are required for optimal health. We will now consider the physiological consequences of suboptimal levels of EFAs in the body as an introduction to why we should ensure that we receive adequate dietary supplies of these important nutrients.

A. Essential Fatty Acid Requirements of Infants

The tissues with the highest concentration of EFAs in the body are the brain and retina. Moreover, the EFAs of the brain and neurological tissues are almost exclusively DHA and ARA (Crawford et al., 1993). As a result, during the last trimester in utero and for the first 2 years of postnatal life, there is a great demand for dietary DHA and ARA to ensure the nominal development of the central nervous system of the infant. Mothers provide this DHA and ARA from their own internal stores, and it is passed to the fetus across the placenta before birth. After birth, it is provided to the baby through its mother’s breast milk. The mother’s DHA status progressively declines throughout her pregnancy (Al et al., 1995), and the DHA status of an infant from a multiple birth is lower than that of an infant from a singleton birth (Zeijdner et al., 1997).

Infants who are fed infant formulas with no supplemental DHA or ARA have altered blood and brain chemistries compared to infants who are fed breast milk, which provides

a natural supplement of both DHA and ARA. The blood of a formula-fed infant will contain less than half of the DHA of the blood of a breast-fed baby (Carlson et al., 1992; Uauy et al., 1992). Brain DHA levels of formula-fed babies can be as much as 30% lower that those of breast-fed babies (Farquharson et al., 1995; Makrides et al., 1994). Thus, feeding an infant a formula without supplemental DHA and ARA as the sole source of nutrition puts that infant into a deficiency state relative to a breast-fed baby. This is espe- cially problematic for the preterm infant whose brain is still developing and who is no longer receiving DHA from the mother across the placenta (Crawford et al., 1998, 1997).

Many studies have attempted to assess the consequences of such a DHA deficiency in the blood and brain of formula-fed infants by comparing the long-term mental outcomes of breast-fed versus formula-fed infants (Florey et al., 1995; Golding et al., 1997; Horwood and Fergusson, 1998; Lanting et al., 1994; Lucas et al., 1992). The vast majority of these studies have clearly established that even after all the confounding data, including socio- economic status, sex, birth order, etc., have been taken into account, there is still a small but significant advantage (3–4 IQ points) for the breast-fed babies when measured by standard IQ assessment, general performance tests (Anderson et al., 1996), or long-term neurological complications (Lanting et al., 1994).

Recent double-blind and randomized studies have now also compared neurological and visual outcomes of babies fed either formulas containing supplemental DHA or stan-

1992b, 1998; Carlson et al., 1996a) or mental acuity (Agostoni et al., 1995; Carlson et al., 1994; Willatts et al., 1998) were detected with the standard formula-fed babies. These differences were overcome in babies who were fed DHA/ARA-supplemented formulas (Table 2). However, the DHA-supplemented formula-fed babies were not better off than the breast-fed babies. Thus, the unsupplemented formula–fed babies may be at a signifi- cant disadvantage because of the DHA deficiency in the brain and eyes during this early period of life. The single exception to the above observation (Auestad et al., 1997) may have been due to the very low levels of DHA used in the fortified formulas in that particular study (Table 2).

As the result of the need for supplemental DHA and ARA by infants who are not receiving their mother’s milk, several professional organizations have made recommenda- tions that all infant formulas contain supplemental DHA and ARA at the levels normally found in mother’s milk ( Table 3 ). Of particular importance was the recommendation by

a joint select committee of the Food and Agriculture Organisation and the World Health

Table 2 Clinical Studies Comparing Neurological or Visual Outcomes of Infants Fed Formulas with or Without Supplemental DHA and ARA

Sample

Supplementation

Effect of DHA/ARA supplementation Preterm

size

infant studies DHA

ARA 0.33 0.10 1,2

83 Improved rod ERG function (37 wk PCA a ); improved visual acuity (57 wk PCA) 0.20 0.00 3,4

67 Improved visual acuity (4 mo); improved visual infor- mation processing (12 mo) 0.20 0.00 5–7

59 Improved visual acuity (2 mo); improved mental acu- ity (12 mo); improved visual recognition memory and visual attention (12 mo)

Term infant studies

DHA ARA 0.30 0.44 8 86 Improved psychomotor development (4 mo)

0.36 0.01 9 79 Improved visual acuity (16 and 30 wk) 0.12 0.43 10 58 Improved visual acuity (2 mo)

No difference 0.25 0.40 12 44 Improved problem solving ability (10 mo)

Improved visual acuity (1.5 and 12 mo) 0.32 0.06 14 54 No significant difference (positive trend) in visual acu-

ity (4 mo) b

a PCA, postconceptual age. b Formula also contained high levels of EPA (0.4%) and GLA (0.54%).

Sources : 1 Birch et al., 1992a, 2 Hoffman et al., 1993, 3 Carlson et al., 1993, 4 Werkman and Carlson, 1996, 5 Carlson et al., 1994, 6 Carlson and Werkman, 1996, 7 Carlson et al., 1996b, 8 Agostoni et al., 1995, 9 Makrides et al., 1995, 10 Carlson et al., 1996a, 11 Auestad et al., 1997, 12 Willatts et al., 1998, 13 Birch et al., 1998, 14 Horby Jorgensen et al.,

Table 3 Recommendations by Expert Panels for the Supplementation of Infant Formula with DHA and ARA

BNF a ISSFAL b FAO/WHO c

Year

1995 Preterm ARA (% of formula fat)

1.0–1.5% 1.0% DHA (% of formula fat)

0.5–1.1% 0.8% Full-term ARA (% of formula fat)

0.6% DHA (% of formula fat)

0.4% EPA/DHA ratio

⬎5:1 10 : 1 a British Nutrition Foundation (Garton, 1992).

b International Society for the Study of Fatty Acids and Lipids (ISSFAL, 1994). c Food and Agriculture Organization/World Health Organization (FAO/WHO, 1993).

Organisation which drew on the expertise of nearly 50 researchers in this field, and con- cluded that adequate dietary DHA was also important for the mother postnatally, prena- tally, and even preconceptually (Crawford, 1995).

B. Essential Fatty Acids and Visual Function

Visual tissues are an extension of the tissues of the central nervous system, and in the multilamellar membranes of the retinal rods [rod outer segments (ROS)] we find the high- est local concentration of DHA in the body. The phospholipids of the ROS are enriched in DHA to levels 50–60% of the total lipid (Salem et al., 1986). Once again, this tissue is unique in that the visual systems of all animals have selected only one of the EFAs— DHA—as the preferred structural unit for this membrane. The ROS membranes are also rapidly cycled with about 10–20% of the distil portion of the stack being resorbed each day, and new membrane formed at the opposite end. Within these cells there is a complex recycling mechanism in place to reuse the DHA each day for the formation of the new membrane (Anderson et al., 1992; Bazan et al., 1993).

Several pathologies which have a visual dysfunction component also have been shown to be associated with abnormally low levels of circulating DHA. These include retinitis pigmentosa (Hoffman and Birch, 1995; Schaefer et al., 1995), certain peroxisomal disorders (e.g., Zellweger’s, Refsum’s, and Batten’s diseases) (Gillis et al., 1986; Infante and Huszagh, 1997; Martinez, 1990, 1996), long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) (Gillingham et al., 1997), and even dyslexia (Stordy, 1995). In some of these cases, clinical studies have shown that dietary DHA supplementation has not only improved the EFA status of the patient, but also significantly improved their visual function ( Table 4 ). Individuals with dyslexia generally have poor night vision, and

a supplementation study with DHA (and EPA provided as fish oil) has recently shown significant improvements in dark adaptation or night vision (Stordy, 1995). Such a result would be expected if the elevation of DHA in the ROS of such affected patients would also elevate the concentration of rhodopsin in those membranes as has been previously been reported in animal studies (Suh et al., 2000). Supplementation with DHA has resulted in significant improvements in visual function in infants with peroxisomal disorders (Mar- tinez, 1996) and even in children with a degenerative visual function such as LCHADD

Table 4 Examples of Clinical Conditions Improved with Essential Fatty Acid Supplementation

Condition Supplementation results Neurological

Zelweger’s Syndrome Improved visual and physical outcome 1 ; remyelination in brain 2 Batten’s disease

Arrested natural course of disease 3

Schizophrenia Significant improvement in schizophrenic symptoms 4 Alzheimer’s disease

Improvement of mental function 5

Bipolar depression Increased time periods between manic phases 6 LCHADD

Significant improvement of vision (VEP) 7 Dyslexia

Improvement of night vision 8

ADD/ADHD

Improvement of attention 9

Cardiovascular Elevated triglycerides

Reduction of triglycerides/elevation of HDL 10 Low HDL

Elevation of HDL 11

Hypertension

Reduction of blood pressure 12

Other Asthma

Improved forced expiratory volume 13

Rheumatoid arthritis

Reduced morning stiffness 14

Diabetic neuropathy Improvement of nerve conduction velocity 15 ; reduction of global Premenstrual syndrome

symptoms of PMS 16

1 (Martinez et al., 1993); 2 (Martinez and Vazquez, 1998); 3 (Bennett et al., 1994); 4 (Laugharne et al., 1996); 5 (Ya- zawa, 1996); 6 (Stoll, 1998); 7 (Gillingham et al., 1997); 8 (Stordy, 1995); 9 (Stordy, 1998); 10 (Davidson et al., 1997);

11 (Mori et al., 1994); 12 (Bonaa et al., 1990); 13 (Dry and Vincent, 1991); 14 (Kjeldsen-Kragh et al., 1992); 15 (Horrobin, 1991); 16 (Oeckerman et al., 1986).

C. Essential Fatty Acids and Neurological Function

The importance of certain essential fatty acids in optimal neurological function is sug- gested by the high concentration of both DHA and ARA in the tissues of the central nervous system. Within the neuronal cells, DHA and ARA are found in highest concentra- tion in the synaptosomal membranes (Suzuki et al., 1997; Wei et al., 1987; Yeh et al., 1993). When rats are made omega-3 deficient by using a feeding regimen completely devoid of omega-3 EFAs, the brain DHA levels are dramatically reduced, the DHA is replaced with the omega-6 counterpart, n-6 docosapentaenoic acid, and the rats have more difficulty with learning tasks (Fujimoto et al., 1989). It is remarkable how this minor change in the molecule (a double bond at the ∆19 position) can contribute so substantially to the performance of the organism as a whole.

Recent studies using nonhuman primates have also demonstrated that early nutrition and/or social interaction has dramatic long-term behavioral consequences that are mani- fested in adolescence and adulthood. Higley and coworkers (1996a,b) have shown that infant Rhesus monkeys who are fed their own mother’s milk (a dietary supply of DHA and ARA) and who are nurtured by their mothers for the first three months of life have remarkably different developmental outcomes than infants raised with a peer group and fed a formula deficient in DHA and ARA. Formula-fed, peer-reared infants develop more aggressive tendencies in adolescence; they are more depressed and never achieve a very high social rank as adults in a free-living monkey colony. These researchers also demon- Recent studies using nonhuman primates have also demonstrated that early nutrition and/or social interaction has dramatic long-term behavioral consequences that are mani- fested in adolescence and adulthood. Higley and coworkers (1996a,b) have shown that infant Rhesus monkeys who are fed their own mother’s milk (a dietary supply of DHA and ARA) and who are nurtured by their mothers for the first three months of life have remarkably different developmental outcomes than infants raised with a peer group and fed a formula deficient in DHA and ARA. Formula-fed, peer-reared infants develop more aggressive tendencies in adolescence; they are more depressed and never achieve a very high social rank as adults in a free-living monkey colony. These researchers also demon-

Attention deficit hyperactivity disorder (ADHD) is also correlated with subnormal serum levels of DHA and ARA. Burgess and coworkers (Stevens et al., 1995) demon- strated that the lower the blood levels of DHA in the ADHD children, the more prevalent were the hyperactivity symptoms. The increase in the incidence of ADHD coincides with the loss of DHA from our diet, and the increasing usage of infant formulas (particularly in the United States) that do not provide supplemental DHA and ARA to an infant early in life. Although it is tempting to propose a causal relationship, the existing data only allow us to conclude that unsupplemented formula feeding is a risk factor for ADHD. McCreadie (1997) also recently showed that formula feeding (lack of early DHA and ARA supplementation) is a significant risk factor for schizophrenia. As in the case of the Rhesus monkeys, it is possible that many long-term behavioral problems may stem from

a suboptimal essential fatty acid status (particularly a deficiency of DHA and ARA) at this crucial period for brain development. Several other neurological pathologies are also related to subnormal levels of DHA in the plasma ( Table 4 ). These include depression (Hibbeln, 1998b; Hibbeln and Salem, 1995; Peet et al., 1998), schizophrenia (Glen et al., 1994; Laugharne et al., 1996) and tardive dyskinesia (Vaddadi et al., 1989). In the latter case, the researchers demonstrated that the symptomology of tardive dyskinesia was most severe in individuals with the low- est DHA levels and that supplementation with omega-3 long chain polyunsaturated fatty acids significantly improved the condition. Preliminary supplementation studies in patients with bipolar disorder (manic depression) using oils rich in DHA and EPA also resulted in a remarkable improvement and significant delay in the onset of symptoms (Stoll, 1998). This result is consistent with the observation by Hibbeln (1998b) that the incidence of major depression seems to be negatively correlated with consumption of fish, the major source of DHA, in a worldwide cross-cultural comparison. A similar correlation can also

be drawn between fish (DHA) in the diet and postpartum depression in women. The brain tissue of patients who were diagnosed with Alzheimer’s dementia (AD) contains about 30% less DHA (especially the hippocampus and frontal lobes) compared to similar tissue isolated from pair-matched geriatric controls (Prasad et al., 1998; Soder- berg et al., 1991). In a 10-year prospective study with about 1200 elderly patients moni- tored regularly for signs of the onset of dementia, it was determined that a low serum phosphatidyl choline DHA (PC-DHA) level was a significant risk factor for the onset of senile dementia (Kyle et al., 1998). Individuals with plasma PC-DHA levels less than 3.5% had a 67% greater risk of being diagnosed with senile dementia in the subsequent

10 years than those with DHA levels higher than 3.5%. Furthermore, for women who had

a least one copy of the Apolipoprotein E4 allele, the risk of attaining a low minimental state exam (MMSE) score went up 400% if their plasma PC-DHA levels were less than 3.5%.

Clinical studies have supported a role of gamma linolenic acid (GLA) in reducing the symptoms of premenstrual syndrome (PMS) (Oeckerman et al., 1986), and GLA- containing products are marketed in Europe with this indication. Perhaps of equal impor- tance have been the reports that supplemental GLA in the diet of diabetics may sig- nificantly improve nerve conduction velocity in individuals with diabetic neuropathy

Finally, perhaps one of the most profound consequences of EFA deficiency is found in patients with a certain inborn error of metabolism related to peroxisomal dysfunction (Martinez, 1991, 1992). As discussed previously, the last steps of the biosynthesis of DHA require one step of β-oxidation of C24:6(6,9,12,15,18,21), which takes place exclusively in the peroxisome ( Fig. 2 ). Certain peroxisomal diseases including Zellweger’s Disease, Refsums’s Disease, and neonatal adrenoleukodystrophy, are accompanied by DHA defi- ciency. The development of these progressive neurodegenerative diseases have been re- cently shown to be arrested if DHA can be reintroduced into the diet at an early stage (Martinez et al., 1993). Much of the neurodegeneration is manifest in a progressive demye- lination, which until now has been thought to be irreversible. Martinez and Vasquez (1998) have recently shown that not only do symptoms improve upon treatment for certain of these patients with DHA, but magnetic resonance imaging data indicate that the brain begins to remyelinate once DHA therapy is initiated.

D. EFAs and Cardiovascular Function

The potential role of essential fatty acids (especially omega-3 fatty acids) in cardiovascular function has been well studied for the last 40 years. Since the first observation by Dyerberg and Bang (1979) that indigenous populations in the Arctic who were consuming large amounts of omega-3 fatty acids (from fish and marine mammals) had a very low incidence of cardiovascular disease, there have been hundreds of clinical studies assessing the effects of fish diets or fish oil pills on cardiovascular outcomes. Several major studies have been completed and many excellent books and reviews on this matter have been written (Chan- dra, 1989; Harris, 1989, 1997; Simopoulos et al., 1986). Most of these studies have con- cluded that the main effects of fish oil supplementation include the reduction of triglycer- ides and an improvement of the HDL/LDL ratio. Furthermore, the effect of EPA on the reduction of platelet aggregation and increase in bleeding time has been viewed as advanta- geous in some respects, but potentially problematic in others. Fish oil supplementation studies have been difficult to interpret because different researchers have used different types of fish oils with different ratios of DHA to EPA and different levels of endogenous cholesterol. Some studies have even shown negative effects (elevation of total cholesterol and LDL cholesterol) with fish oil consumption (FDA, 1993). Furthermore, it may not

be valid to equate whole fish consumption with fish oil consumption since fish gener- ally are a much better source of DHA (DHA/EPA ratio 3–4:1) than are most fish oils (DHA/EPA 0.5:1).

More recently, the antiarrhythmic effect of DHA and other long chain omega-3 fatty acids has been demonstrated. Using a rat model of sudden cardiac death (SCD), McLennan and coworkers (1996) first showed that the frequency of ventricular fibrillation could be significantly reduced by simply predosing the animals with omega-3 LCPUFAs, particu- larly DHA. Billman and colleagues (1997) demonstrated a similar significant reduction in SCD in a dog model by predosing the animals with DHA/EPA. More directly relating the human condition, Siscovick et al. (1995) followed over 250 paramedic responses to cardiac emergencies in the Pacific Northwest and showed that consumption of at least three fatty fish meals per week (about 200 mg DHA/day) reduced the likelihood of dying from SCD by 50%, although it did not decrease the risk that one would have a cardiac emergency.

Although a general triglyceride-lowering effect has been measured with fish oil (a

Table 5 Effects of DHA Supplementation in the Absence of Any Other Supplemental Omega-3 Fatty Acids in Double-Blind, Placebo-Controlled, Clinical Trials

Study 4 a Study 5 Sample size

Measurement Study 1

Study 2

Study 3

55 24 27 32 6 Dose (g DHA/day)

1.6 1.8 1.2 3.0 6.0 Duration (days)

98 42 42 14 90 Blood DHA

⫹26% ns HDL

ns ns a This supplementation included 3.4g ARA/day in addition to the DHA.

Sources : Study 1, Agren et al., 1996; Study 2, Conquer and Holub, 1996; Study 3, Davidson et al., 1997; Study 4, Innis and Hansen, 1996; Study 5, Nelson et al., 1997b.

issue by using a single cell algal oil which contains only DHA and no EPA or any other LC-PUFA. Five such studies have now been published (Agren et al., 1996; Conquer and Holub, 1996; Davidson et al., 1997; Innis and Hansen, 1996; Nelson et al., 1997b) and it is clear that DHA alone can reduce serum triglycerides by about 20%, and specifically elevate HDL by about 10% (Table 5). Interestingly, in those studies with the DHA oil, none of the researchers reported any change in platelet aggregation or bleeding time in spite of a relatively high rate of intake (up to 6.0 g DHA/day). Kelley et al. (1998) further showed that the DHA oil supplementation also had little or no effect on various immuno- logical parameters. This is quite unlike fish oils (EPA/DHA combinations), which are classically known for their effect on the down-regulation of the immune response and inflammation. As is the case with the decreased platelet aggregation by EPA, the down- regulation of the immune function may be advantageous for some conditions, but problem- atic for others.