The effect of dietary docosahexaenoic acid on platelet function, platelet fatty acid composition, and blood coagulation in humans

The effect of dietary docosahexaenoic acid (DHA) in the absence of eicosapentaenoic acid (EPA) has been studied infrequently in humans under controlled conditions. This 120-d study followed healthy, adult male volunteers who lived in the metabolic research unit (MRU) of the Western Human Nutrition Research Center for the entire study. The basal (low-DHA) diet consisted of natural foods (30 en% fat, 15 en% protein, and 55 en% carbohydrate), containing <50 mg/d of DHA, and met the recommended daily intake for all essential nutrients. The high-DHA (intervention) diet was similar except that 6 g/d of DHA in the form of a triglyceride containing 40% DHA replaced an equal amount of safflower oil in the basal diet. The subjects (ages 20 to 39) were within −10 to +20% of ideal body weight, nonsmoking, and not allowed alcohol in the MRU. Their exercise level was constant, and their body weights were maintained within 2% of entry level. They were initially fed the low-DHA diet for 30 d. On day 31, six subjects (intervention, group A) were placed on the high-DHA diet; the other four subjects (controls, group B) remained on the low-DHA diet. Platelet aggregation in platelet-rich plasma was determined using ADP, collagen, and arachidonic acid. No statistical differences could be detected between the amount of agonist required to produce 50% aggregation of platelet-rich plasma before and after the subjects consumed the high-DHA diet. The prothrombin time, activated partial thromboplastin time, and the antithrombin-III levels in the subjects were determined, and, again, there were no statistically significant differences in these three parameters when their values were compared before and after the subjects consumed the high-DHA diet. In addition, the in vivo bleeding times did not show any significant difference before and after the subjects consumed the high-DHA diet (9.4 ±3.1 min before and 8.0±3.4 min after). Platelets from the volunteers exhibited more than a threefold increase in their DHA content from 1.54±0.16 to 5.48±1.21 (wt%) during the DHA feeding period. The EPA content of the subjects’ platelets increased from 0.34±0.12 to 2.67±0.91 (wt%) during the high-DHA diet despite the absence of EPA in the subjects’ diets. The results from this study on blood clotting parameters and in vitro platelet aggregation suggest that adding 6 g/d of dietary DHA for 90 d to a typical Western diet containing less than 50 mg/d of DHA produces no observable physiological changes in blood coagulation, platelet function, or thrombotic tendencies in healthy, adult males.     

Differential utilization of eicosapentaenoic acid and docosahexaenoic acid in human plasma

It has recently been shown that the ω3 fatty acid status in humans can be predicted by the concentration of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in plasma phospholipids [Bjerve, K.S., Brubakk, A.M., Fougner, K.J., Johnsen, H., Midjthell, K., and Vik, T. (1993)Am. J. Clin. Nutr., in press]. In countries with low intake of ω3 fatty acids, the level of EPA in plasma phospholipids is often only about one-fifth the concentration of DHA. The purpose of this study was to investigate whether this difference in the concentration of these two fatty acids was due to a selective loss of EPA relative to DHA or to a lower dietary intake of EPA. Seven female volunteers ingested four grams of MaxEPA daily for 2 wk and in the following 4 wk they ate a diet almost completely devoid of the long-chain ω3 fatty acids. The concentrations of the ω3 fatty acids in the plasma cholesteryl esters, triglycerides and phospholipids and the high density lipoprotein phospholipids were examined at weekly intervals throughout the study. There was a more rapid rise in the concentration of EPA than in DHA levels in the supplementation period in all lipid fractions, but there was a disproportionate rise in DHA relative to EPA in the plasma lipids compared with the ratio in the supplement. In the depletion phase there was a rapid disappearance of EPA from all fractions, such that pre-trial levels were reached by one week post-supplementation. The disappearance of DHA was slower, particularly for the plasma phospholipids: at 4 wk post-supplementation, the DHA concentration in this fraction was still 40% above the pre-trial value. It is suggested that the low plasma EPA values relative to DHA are the result of increased β-oxidation of EPA and/or low dietary intake, rather than a rapid conversion of EPA to DHA. One practical result of this experiment is that, compared with DHA, the maintenance of increased EPA levels in plasma (and therefore tissues) would require constant inputs of EPA due to its more rapid loss from the plasma.     

Differential effects of eicosapentaenoic acid and docosahexaenoic acid on human skin fibroblasts

To better understand the mode of action of ω3 fatty acids in cell membranes, human foreskin fibroblasts were grown in serum-free medium supplemented with 50 μM oleic acid linoleic acid, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), and the effects on membrane composition, fluorescence polarization and enzyme activities were followed. The cells were enriched with EPA and DHA up to 7 and 13% of total lipids, respectively, of which >95% was associated with phospholipids. In addition, the concentration of 22∶5n−3 increased with both EPA and DHA to 7.5, and 2.1% of the total fatty acids, respectively. When compared to controls (oleic acid), cells treated with DHA showed a decrease in cholesterol, phospholipids, arachidonic acid (AA) and free cholesterol/phospholipid ratio (P<0.05). In the presence of EPA, only decreases in AA and cholesterol were significant (P<0.05). Membrane fluidity, assessed by fluorescence anisotropy, was increased 16% in cells enriched with DHA (P<0.05), but showed no change with EPA or linoleic acid. There was an increase in membrane-associated 5′-nucleotidase (+27%) and adenylate cyclase (+19%) activities (P<0.05), in DHA-enriched, but not in EPA-enriched cells, when compared with oleate controls. The studies show that incorporation of DHA, but not EPA, into cell membranes of fibroblasts alters membrane biophysical characteristics and function. We suggest that these two major n−3 fatty acids of fish oils have differential effects on cell membranes, and this may be related to the known differences in their physiological effects.     

Pathophysiologic role of redox status in blood platelet activation. Influence of docosahexaenoic acid

Decrease of platelet glutathione peroxidase activity results in increased life span of lipid hydroperoxides, especially the 12-lipoxygenase product of arachidonic acid, 12-HpETE. Phospholipase A₂ activity is subsequently enhanced with the release of arachidonic acid, which results in higher thromboxane formation and platelet function. Docosahexaenoic acid may either potentiate platelet lipid peroxidation or lower it when used at high or low concentrations, respectively. In the case of slowing down lipid peroxidation, docosahexaenoic acid was specifically incorporated in plasmalogen ethanolamine phospholipids. This could have a relevant pathophysiologic role in atherothrombosis.     

Acylation of docosahexaenoic acid into phospholipids by intact human neutrophils

Docosahexaenoic acid was not only acylated into phospholipids but also into triacylglycerols by intact human neutrophils. The distribution of radiolabeled docosahexaenoic acid among individual phospholipids was dependent on the incubation time. [1-¹⁴C]Docosahexaenoic acid at all concentrations (1 to 8 μM) was acylated mainly into phosphatidic acid after 1–2 min incubation, and the radioactivity of phosphatidic acid started to decline after a longer period of incubation, suggesting the participation of docosahexaenoyl-phosphatidic acid in the synthesis of other glycerolipids. It was acylated primarily into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) after a 2-hr incubation. The labeled phosphatidic acid may be rapidly deacylated and the 22∶6(n−3) moiety is then reacylated into other lysophospholipids. The low levels of [¹⁴C]22∶6(n−3) in 1,2-diacylglycerol suggest that the deacylation-reacylation cycle may be a major pathway in the formation of [¹⁴C]22∶6(n−3)-PC and-PE in intact neutrophils. This n−3 fatty acid was a relatively poor substrate for acylation into phosphatidyl-inositol as compared to arachidonic acid and eicosapentaenoic acid. However, the patterns of distribution of all three polyunsaturated fatty acids among the diacyl-and ether-linked class compositions of PC and PE were similar. These data suggest the potential of increasing the content of docosahexaenoic acid of membrane lipids in neutrophils by dietary supplement of this fatty acid.     

15-hydroperoxyeicosatetraenoic acid inhibits human platelet aggregation

Using human platelets isolated from their plasma, we showed that 15-hydroperoxy-eicosatetraenoic acid (15-HPETE) inhibits platelet aggregation induced either by arachidonic acid or prostaglandin H₂ analog. 15-HPETE does not modify platelet prostaglandin and thromboxane formation from exogenous arachidonic acid but does decrease platelet lipoxygenase activity.     

The docosahexaenoic acid of marine organisms

Preparative gas chromatography has been used for the purification of the highly unsaturated C₂₂ acid present in cod liver. Confirmation that this acid is Δ^{4,7,10,13,16,19} docosahexaenoic acid has been obtained by purely physicochemical means using NMR and mass spectrometry.     

Blood lipid docosahexaenoic and arachidonic acid in term gestation infants fed formulas with high docosahexaenoic acid,low eicosapentaenoic acid fish oil

The effect of fish oil high in docosahexaenoic acid (22∶6n−3) and low in eicosapentaenoic acid (20∶5n−3) in formula on blood lipids and growth of full-term infants was studied. Infants were fed formula with about 15% oleic acid (18∶1), 32% linoleic acid (18∶2n−6), 4.9% linolenic acid (18∶3n−3) and 0, 0.10 or 0.22% 22∶6n−3, or 35% 18∶1, 20% 18∶2n−6, 2.1% 18∶3n−3 and 0, 0.11 or 0.24% 22∶6n−3 from 3 d to 16 wk of age (n=16, 18, 17, 21, 17, 16, respectively). The formulae had <0.1% 20∶5n−3 and no arachidonic acid (20∶4n−6). Breast-fed infants (n=26) were also studied. Plasma phospholipid and red blood cell (RBC) phosphatidylcholine (PC) and phosphatidylethanolamine (PE) fatty acids were determined at 3 d and 4, 8, and 16 wk of age. These longitudinal analyses showed differences in blood lipid 22∶6n−3 between breast-fed and formula-fed infants depending on the feeding duration. At 16 wk, infants fed formula with 0.10, 0.11% 22∶6n−3, or 0.22% 22∶6n−3 had similar 22∶6n−3 levels in the plasma phospholipid and RBC PC and PE compared with breast-fed infants and higher 22∶6n−3 than infants fed formula without 22∶6n−3. Formula with 0.24% 22∶6n−3, however, resulted in higher plasma phospholipid 22∶6n−3 than in breast-fed infants at 16, but not 4 or 8 wk of age. Plasma and RBC phospholipid 20∶4n−6 was lower in formula-fed than breast-fed infants, but no differences in growth were found. Higher blood lipid C₂₀ and C₂₂ n−6 and n−3 fatty acids in infants fed formula with 20% 18∶2n−6 and 2.4% 18∶3n−3 compared with 32% 18∶2n−6 and 4.9% 18∶3n−3 show the increase in blood lipid 22∶6n−3 in response to dietary 22∶6n−3 depending on other fatty acids in the formula.     

Enrichment of eicosapentaenoic acid and docosahexaenoic acid in saponified menhaden oil

Eicosapentaenoic acid (EPA, 20∶5n−3) and docosahexaenoic acid (DHA, 22∶6n−3) in free fatty acids (FFA) derived from saponified menhaden oil were concentrated by the solubility differences of FFA-salts in organic solvent. FFA-salts were formed by adding NaOH to a solution containing FFA. A Buchner funnel was used to separate solid phases from liquids containing FFA-salts. FFA that are rich in EPA and DHA can be recovered from the liquid phase by the addition of 12 N HCl. The effects of reaction time, the amount of NaOH, and solvent used on the concentration of EPA and DHA were systematically investigated. With a total volume of 112 mL, made up of 1.85% 15 N NaOH, 88.1% acetone, and 10.0% FFA, a reaction temperature of 30°C, and a reaction time of 1 h, the resulting liquid phase contained 65.4 wt% EPA and DHA, with a corresponding yield of 41.5%. By replacing the acetone with a mixture of 45% acetone and 55% acetonitrile and then storing the liquid phase at −70°C overnight, the content and yield of EPA and DHA in the final liquid phase were 61.4 wt% and 66.2%, respectively.     

Preparation of highly purified concentrates of eicosapentaenoic acid and docosahexaenoic acid

Because of the complexity of marine lipids, polyunsaturated fatty acid (PUFA) derivatives in highly purified form are not easily prepared by any single fractionation technique. The products are usually prepared as the ethyl esters by esterification of the body oil of fat fish species and subsequent physicochemical purification processes, including short-path distillation, urea fractionation, and preparative chromatography. Lipase-catalyzed transesterification has been shown to be an excellent alternative to traditional esterification and short-path distillation for concentrating the combined PUFA-content in fish oils. At room temperature in the presence of Pseudomonas sp. lipase and a stoichiometric amount of ethanol without any solvent, efficient transesterification of fish oil was obtained. At 52% conversion, a concentrate of 46% eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) was obtained in excellent recovery as a mixture of mono-, di-, and triacylglycerols. The latter can be easily separated from the saturated and monounsaturated ethyl esters and converted into ethyl esters either by conventional chemical means or enzymatically by immobilized Candida antarctica lipase. Urea-fractionation of such an intermediary product can give an EPA+DHA content of approximately 85%.     

Dietary docosahexaenoic acid and immunocompetence in young healthy men

The purpose of this study was to examine the effect of dietary docosahexaenoic acid (DHA), in the absence of eicosapentaenoic acid, on human immune response (IR). A 120-d study with 11 healthy men was conducted at the Metabolic Research Unit of the Western Human Nutrition Research Center. Four subjects (control group) were fed the stabilization or basal diet (15, 30, and 55% energy from protein, fat, and carbohydrate, respectively) throughout the study; the remaining seven subjects (DHA group) were fed the basal diet for the first 30 d, followed by 6 g DHA/d for the next 90 d. DHA replaced an equivalent amount of linoleic acid; the two diets were comparable in their total fat and all other nutrients. Both diets were supplemented with 20 mg d-α-tocopherol acetate per day. Indices of IR were examined on study day 22, 30, 78, 85, 106, and 113. Addition of DHA at moderately high levels did not alter the proliferation of peripheral blood mononuclear cells cultured with phytohemag-glutinin or concanavalin A, or the delayed hypersensitivity skin response. Also, additional DHA did not alter the number of T cells producing interleukin 2 (IL2), the ratio between the helper/suppressor T cells in circulation, or the serum concentrations of immunoglobulin G, C3, and interleukin 2 receptor (IL2R). DHA supplementation, however, caused a significant (P=0.0001) decrease in the number of circulating white blood cells which was mainly due to a decrease in the number of circulating granulocytes. The number of lymphocytes in peripheral circulation was not affected by Dietary DHA enrichment, but the percentage of lymphocytes in white blood cells increased because of a reduction in granulocyte numbers. None of these indices was changed in the control group. Our results show that when total fat intake is low and held constant, DHA consumption does not inhibit many of the lymphocyte functions which have been reported to be inhibited by fish oil consumption.     

Eicosapentaenoic acid and docosahexaenoic acid production potential of microalgae and their heterotrophic growth

Twenty microalgal strains were investigated in photoautotrophic flask cultures for their potential for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) production. The highest EPA proportion (% of total fatty acids) was produced by Monodus subterraneus UTEX 151 (34.2%), followed by Chlorella minutissima UTEX 2341 (31.3%) and Phaeodactylum tricornutum UTEX 642 (21.4%). The highest DHA proportion (% of total fatty acids) was obtained in Crypthecodinium cohnii UTEX L1649 (19.9%), followed by Amphidinium carterae UTEX LB 1002 (17.0%) and Thraustochytrium aureum ATCC 28211 (16.1%). Among the 20 strains screened, the EPA yield was high in M. subterraneus UTEX 151 (96.3 mg/L), P. tricornutum UTEX 642 (43.4 mg/L), Chl. minutissima UTEX 2341 (36.7 mg/L), and Por. cruentum UTEX 161 (17.9 mg/L) owing to their relatively high biomass concentrations. The DHA yield was high in C. cohnii UTEX L1649 (19.5 mg/L) and A. carterae UTEX LB 1002 (8.6 mg/L). Heterotrophic growth of these 20 microalgae was also tested on two different carbon sources, acetate and glucose. All microalgae except Nannochloropsis oculata UTEX LB 2164 showed growth on glucose (5 g/L) under heterotrophic conditions. Twelve of them could grow heterotrophically when acetate (1 g/L) was used as their sole carbon and energy source.     

Potentiating effect of 5,8,11-eicosatrienoic acid on human platelet aggregation

5,8,11-Eicosatrienoic acid (20∶3ω9), a fatty acid increased in the platelet phospholipids of man and animals fed saturated fats, was either added to human platelets simultaneously with the aggregating agents, or incorporated into the platelet phospholipids by preincubation. 20∶3ω9 markedly increased the response of platelets to all aggregating agents tested when added simultaneously with the agent, but solely to thrombin and ionophore, after incorporation into the platelet phospholipids. The potentiating effects of 20∶3ω9 on thrombin aggregation do not appear to be related to prostaglandin formation, but rather to the production of a monohydroxy derivative through the lipoxygenase pathway.     

The effect of peroxidized arachidonic acid upon human platelet aggregation

Human platelet aggregation was studied in vitro following exposure to free arachidonic acid and peroxidized arachidonic acid. A slow aggregation response was caused by free arachidonic acid, whereas a rapid, marked response resulted from exposure to peroxidized free arachidonic acid. Aggregation resulting from peroxidized arachidonic acid was not counteracted by adenosine nor by prostaglandin E₁, both in high concentrations. Peroxide-induced platelet aggregation required the presence of added calcium ions in vitro. The aggregation resulting from exposure to peroxidized arachidonic acid was abolished by prior treatment of the lipid peroxide with tocopherol and butylated hydroxy toluenne.     

Increased docosahexaenoic acid levels in human newborn infants by administration of sardines and fish oil during pregnancy

In rhesus monkeys, maternal n-3 fatty acid deficiency during pregnancy produces infant monkeys deficient in n-3 fatty acids at birth. These results stimulated current experiments to find out if n-3 fatty acids from fish in the diets of pregnant women would influence the concentration of docosahexaenoic acid (DHA, 22:6 n-3) in the newborn human infant. Fifteen healthy pregnant women were enrolled to receive a 9-wk dietary supplementation of n-3 fatty acids from the 26th to the 35th wk of pregnancy. Sixteen pregnant women were not supplemented and served as controls. n-3 Fatty acid supplementation consisted of sardines and additional fish oil, which provided a total of 2.6 g of n-3 fatty acids per day (d) for the 9-wk period of supplementation. This included 1.01 g DHA. The end point of this study was the blood concentrations of DHA in the newborn infant. DHA in maternal red blood cells increased from 4.69% of total fatty acids to 7.15% at the end of the supplement period and at the time of delivery decreased (as expected) to 5.97% of total fatty acids. Maternal plasma showed a similar change from 2.12 to 3.51% of total fatty acids and then decreased to 2.35%. Levels of DHA in plasma and red blood cells of unsupplemented mothers did not change during the same time period. Levels of DHA in blood of newborn infants differed greatly in infants born from n-3-supplemented mothers compared with control infants. In red blood cells, DHA was 7.92% of total fatty acids compared with 5.86% (control infants). Plasma values showed a similar difference: 5.05% vs. 3.47% (controls). In n-3-supplemented infants, DHA concentrations were 35.2% higher than in control infants in red blood cells and 45.5% higher in plasma. These data indicate the importance of maternal dietary n-3 fatty acids and, in particular, maternal dietary DHA in promoting higher concentrations of DHA in the blood of the newborn infant.     

Monitoring the oxidation of docosahexaenoic acid in lipids

The oxidation of free DHA, DHA mixed with PC, and DHA incorporated into PC, PE, or TG was evaluated to determine which lipid provided DHA with the best protection against oxidation. DHA was either situated at the sn-1 position, sn-2 position, or both positions of the phospholipid, whereas the TG contained DHA at all positions. All lipids were incubated as bulk lipids, in chloroform, or as an emulsion in contact with air at 25–30°C for 28 d. Since DHA, which is highly sensitive to oxidation, has a great impact on our health and is desired as a food additive, the stability of this FA is of great importance. This study was mainly focused on the primary oxidation products, which were monitored as eight monohydroperoxy-DHA isomer groups, the total amount of polyhydroperoxides, and the PV. However, a measure of secondary oxidation products, the carbonyl value, was also monitored. We found that DHA was most protected against hydroperoxide formation when it was incorporated at one position of either PC or PE. In these lipids, hydroperoxide formation at carbon atoms 4, 7, 8, and 11 was completely prevented. DHA mixed with PC was also protected, although to a lesser extent, and all hydroperoxide isomers were detected. In contrast, PC and TG containing DHA at all positions should be avoided, since they were highly oxidized.     

Enzymatic and chemical synthesis of phosphatidylcholine regioisomers containing eicosapentaenoic acid or docosahexaenoic acid

Regioselective incorporation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into phosphatidylcholine (PC) was carried out using enzymatic and chemical synthesis. Incorporation at the sn‐1 position was successfully achieved by lipase‐catalysed esterification of 2‐palmitoyl‐lysophosphatidylcholine (LPC), although in most cases, the enzymes incorporated EPA and DHA at lower rates than other fatty acids. For the incorporation of DHA, Candida antarctica lipase B was the only useful enzyme, while incorporation of EPA was efficiently carried out using either this enzyme or Rhizopus arrhizus lipase. The highest yields in the lipase‐catalysed reactions were obtained at the lowest water activity (close to 0). However, by carrying out the reactions at a higher water activity of 0.22, more EPA and DHA were incorporated. Esterification of 2‐palmitoyl‐LPC with pure EPA at this water activity converted 66 mol‐% of LPC to PC using Rhizopus arrhizus lipase as catalyst. When the fatty acid was DHA and the catalyst Candida antarctica lipase B, 45 mol‐% of PC was obtained. For incorporation of EPA and DHA at the sn‐2 position, phospholipase A₂ was used, but the reaction was very slow. Chemical coupling of 1‐palmitoyl‐LPC and EPA or DHA was more efficient, resulting in complete conversion of LPC.     

The role of docosahexaenoic acid in retinal function

An important role for docosahexaenoic acid (DHA) within the retina is suggested by its high levels and active conservation in this tissue. Animals raised on n-3-deficient diets have large reductions in retinal DHA levels that are associated with altered retinal function as assessed by the electroretinogram (ERG). Despite two decades of research in this field, little is known about the mechanisms underlying altered retinal function in n-3-deficient animals. The focus of this review is on recent research that has sought to elucidate the role of DHA in retinal function, particularly within the rod photoreceptor outer segments where DHA is found at its highest concentration. An overview is also given of human infant studies that have examined whether a neonatal dietary supply of DHA is required for the normal development of retinal function.     

Effects of an eicosapentaenoic and docosahexaenoic acid concentrate on a human lung carcinoma grown in nude mice

The effects of the n−3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on the growth of a human lung mucoepidermoid carcinoma (HLMC) in athymic mice were studied. The mice were divided into three groups which were given either a control chow diet (C), a chow diet supplemented with EPA/DHA (P) (25 or 50 mg of free n−3 fatty acids/g of pellet/day), or chow diet supplemented with palmitic acid (S) (isocaloric with P). Two independent experimental schedules were followed: i) host mice bearing either tumors that were allowed to reach 4000 mm³, or only 35 mm³, were fed C, P or S for 21 or 41 days; ii) animals were fed C, P and S for 9 days before tumor implant and were maintained on these diets throughout tumor growth. Food consumption, mouse weight and liver/body weight ratio showed no significant differences between supplemented diets and chow. Tumor growth was markedly inhibited (45%) in both experiments by the EPA/DHA supplemented diet. In Experiment 2, only 60% of mice fed diet P had tumors. The fatty acid composition of neutral and polar lipids of host liver and tumor reflected the dietary intake of n−3 fatty acids; the content of arachidonic acid was reduced by 50%, and EPA/DHA was increased 3-to 5-fold. Tumor prostaglandin E₂ levels were reduced 7.4-fold in the P group. The reduced PGE₂ content may be a factor in tumor growth inhibition. Preliminary data were presented at the Annual Meeting of the American Oil Chemists' Society, (1990), Baltimore, MD, (de Antueno, R.J., Bravo, M.G. de, Toledo, J., De Tomas, M.E., Mercuri, O., Quintans, C. (1990)INFORM 1, 328 (Abstract HH1).     

Dietary docosahexaenoic acid as a source of eicosapentaenoic acid in vegetarians and omnivores

The utilization of dietary docosahexaenoic acid (DHA; 22:6n−3) as a source of eicosapentaenoic acid (EPA; 20:5n−3) via retroconversion was investigated in both vegetarians and omnivores. For this purpose, an EPA-free preparation of DHA was given as a daily supplement (1.62 g DHA) over a period of 6 wk. The dietary supplement provided for a marked increase in DHA levels in both serum phospholipid (from 2.1 to 7.1 mol% in vegetarians and 2.2 to 7.6 mol% in omnivores) and platelet phospholipid (from 1.1 to 3.4 mol% in vegetarians and 1.4 to 3.9 mol% in omnivores). EPA levels rose to a significant but much lesser extent, while 20:4n−6, 22:5n−6, and 22:5n−3 all decreased. Based on the serum phospholipid data, the retroconversion of DHA to EPA in vivo was estimated to be 9.4% overall with no significant difference between omnivores and vegetarians.