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Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:3384-3391

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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:3384-3391.)
© 1997 American Heart Association, Inc.

Articles

Dietary Fish Oil (4 g Daily) and Cardiovascular Risk Markers in Healthy Men

Peter Marckmann; Else-Marie Bladbjerg; ; Jørgen Jespersen

From the Research Department of Human Nutrition, Royal Veterinary and Agricultural University, Frederiksberg (P.M.), and the Institute for Thrombosis Research, South Jutland University Centre, Esbjerg (E.-M.B., J.J.), Denmark.

Correspondence to Peter Marckmann, Research Department of Human Nutrition, Rolighedsvej 30, DK-1958 Frederiksberg, Denmark. E-mail pma{at}kvl.dk


*    Abstract
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 *Abstract
down arrowIntroduction
 down arrowMethods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Abstract Some epidemiological observations indicate that 1 to 2 weekly servings of fish prevent ischemic heart disease (IHD). This might be explained by an effect of the very-long-chain n-3 polyunsaturated fatty acids (n-3 VLCPUFA) of fish oil on lipid metabolism and/or the hemostatic system, both involved in IHD development. We studied the effect of incorporating natural fish oil (4 g daily equivalent to 0.91 g n-3 VLCPUFA and corresponding to one to two weekly servings of fatty fish) into the diet in a 4-week parallel, randomized, and double-blind trial of 47 healthy males aged 29 to 60 years. Sunflower oil was used as placebo. The fish oil had no significant effect on plasma lipids, apolipoproteins, lipoprotein(a), blood coagulation FVII, fibrinogen, endogenous fibrinolysis, ß-thromboglobulin, von Willebrand factor, glucose, or insulin in fasting blood samples. In nonfasting samples (n=19), fish oil was associated with an approximately 30% decline in plasma triglycerides (P<.02) and a 9% decline in FVII protein (P<.05), whereas FVII coagulant activity and fibrinolysis were unaffected. In conclusion, our findings indicate that lowering of postprandial triglycerides is the only n-3 VLCPUFA effect that could contribute to primary prevention of IHD in healthy middle-aged men as assessed by currently measurable lipid and hemostatic risk markers.


Key Words: fibrinogen • nutrition • blood coagulation factor VII • triglycerides • fibrinolysis


*    Introduction
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 up arrowAbstract
 *Introduction
down arrowMethods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Western populations are advised to increase their fish intake because of its putative beneficial effect on the risk of ischemic heart disease (IHD).1 The n-3 very-long-chained polyunsaturated fatty acids (n-3 VLCPUFA) of fish oil may be the nutrients that bring about any cardiovascular effect of fish.2 3 4 If so, incorporation of fish oil into high-fat foods present in the habitual diet could be an alternative way to lower the risk of IHD. Soft margarines and vegetable oils are eaten in considerable amounts (25 to 50 g daily) by Western populations. The incorporation of fish oil into such products would be an obvious and appropriate way in which to increase the average n-3 VLCPUFA consumption.

In the present study, we examined the effect of incorporating fish oil (4 g daily) into a sunflower oil–based margarine on a series of important cardiovascular risk markers. The study included measurements of blood lipids, blood coagulation FVII, and the fibrinolytic system in the fasting and the postprandial state and gives a comprehensive impression of the physiological impact of a moderately increased consumption of n-3 VLCPUFA. In addition, the link between dietary fat, plasma triglycerides, and postprandial activation of blood coagulation FVII was elucidated.


*    Methods
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 up arrowIntroduction
 *Methods
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Fifty nonobese, healthy males were recruited for the study. All had a low habitual consumption of fish (inclusion criterion; i.e., hot fish meals not more than once weekly or no daily sandwich topping with fish or fish products). None were taking fish oil capsules or were using pharmaceuticals on a regular basis (exclusion criteria). Two individuals dropped out because of intercurrent disease, and one was excluded because of permanently raised serum concentrations of CRP (inflammatory disease indicator). The average age of the remaining 47 individuals was 41 years (SD 9, range 29 to 60 years). Body weights averaged 77.7 kg (SD 8.8, range 55.6 to 95.7) and body mass indices 24.1 kg/m2 (SD 2.5, range 18.4 to 29.3). Eight participants were light smokers (average, 3 cigarettes per day, range 1 to 7). The protocol was approved by the Ethical Committee of Frederiksberg and Copenhagen, and informed consent was obtained from the volunteers according to the Helsinki declaration.

Two margarines were produced for the study and delivered in 15-g units with a color-coding lid. SUN was a conventional margarine based on sunflower oil with a 16% water content. FISH was similar to SUN except for the replacement of 2 g of sunflower oil per 15 g of margarine with 2 g of fish oil (Aarhus Olie). The fatty acid composition of the two margarines is presented in Table 1Down.


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  		Table 1. Fatty Acid Composition (g/100 g Fat) of the Two Margarines, SUN and FISH, According to the Manufacturer (Aarhus Olie, Aarhus, Denmark)

Study Design
The study was parallel, randomized, and double blind. Its total duration was 7 weeks: a 3-week run-in period and a 4-week intervention period. The participants ate 30 g (2 units) margarine per day all 7 weeks and were instructed to use it solely as a spread. SUN was the only margarine used during the run-in period. Volunteers were randomly allocated to SUN (n=24) or FISH (n=23) margarine during the intervention period. Each 30 g of FISH contained 0.91 g n-3 VLCPUFA (C20:5+C22:5+C22:6). Fasting blood samples were drawn from all participants immediately before and after the 4-week intervention. A subgroup of volunteers participated in meal tests in the last week of the run-in and the intervention period. Besides consuming the margarines, the participants were free to eat according to their personal preferences. They were asked, however, not to undertake conscious dietary changes during the study period.

Test Meals
Nineteen participants took part in the meal tests (9 from the SUN group, 10 from the FISH group). On each of the two test days near the end of the run-in and intervention periods, breakfast was served at 9 AM (required to be consumed within 20 minutes) and lunch at 11 AM (required to be eaten within 30 minutes).

The breakfast consisted of white bread (90 g), black currant marmalade (20 g), hard cheese (40 g), whole milk (150 g), test margarine (30 g SUN/FISH), and water ad lib. The total energy content was 3.3 MJ, with 56% coming from fat (49 g). Saturated fatty acids contributed 44%, monoenes 30%, and polyenes 26% of all fatty acids.

The lunch was composed of white bread (75 g), butter (45 g), liver paste (50 g), hard cheese (40 g), cheese spread (30 g), cucumber, green salad, tomatoes, and green pepper (total 90 g), vanilla ice cream (100 g), whipped cream (30 g), black currant marmalade (25 g), and water ad lib. The total energy content was 5.6 MJ, and the total fat content 99 g, or 67% of energy. Saturated fatty acids contributed 64%, monoenes 30%, and polyenes 6% of all fatty acids.

Participants were bled at 0800 (fasting), 1030, 1200, 1315, 1430, and 1600 hours on test days. They were allowed to leave the department between the scheduled activities, but no food or beverages besides what was served by us were allowed. The participants abstained from coffee, tea, and tobacco on test days.

Blood Sampling
Subjects refrained from the use of any occasional drugs, including aspirin and other nonsteroid anti-inflammatory medications, for at least 1 week before blood sampling. Intake of alcohol and participation in sports were not allowed during the day before sampling. Finally, the volunteers fasted (no food, beverages, or tobacco apart from 1/2 L of water) from 10 PM the day before sampling.

After at least 10 minutes of supine rest, blood was sampled in a series of evacuated tubes filled in the same fixed order as they are now mentioned. Blood was collected in EDTA tubes for the analysis of plasma lipids and apolipoproteins, in ice-bathed acidified Stabilyte tubes (Biopool) for plasma fibrinolytic variables, in ice-bathed Diatubes (Becton Dickinson) for plasma ß-TG, in ice-bathed citrated tubes for plasma vWF and Lp(a), in ice-bathed EDTA 5-mL tubes to which 10 µL D-Phe-Pro-Arg chloromethyl ketone (2.63 g/L) was immediately added for plasma FbdP and F1+2, in citrated tubes at ambient temperature for plasma FVII and fibrinogen, in heparin tubes with sodium fluoride (Becton Dickinson) for plasma glucose, in tubes without additives for serum insulin and CRP, and in EDTA tubes for analyses of LDL fatty acid composition and oxidation resistance (to be presented separately).

All tubes were spun at the relevant temperature and 3000g for 15 minutes, and aliquots of plasma/serum were then snap-frozen and stored at -80°C until analysis. Plasma for the LDL analyses was stored under an atmosphere of nitrogen.

Blood Analyses
All analyses were performed in one series for each participant. Plasma total cholesterol, HDL cholesterol, and triglyceride concentrations were determined by enzymatic methods (Boehringer Mannheim GmbH) on Cobas Mira+ (Roche Diagnostic Systems, Inc). HDL cholesterol was estimated after precipitation of apolipoprotein B lipoproteins with phosphotungstic acid–MgCl2. Apolipoproteins A-I and B were assayed by turbidimetry (Roche) on Cobas Mira+.

Plasma FVIIc was measured in a one-stage clotting assay using FVII-deficient plasma (Biopool) and human brain tissue factor.5 In the clot assay for FVIIa, mutant recombinant tissue factor was used (Diagnostica Stago). Plasma fibrinogen concentrations were assessed by a modified Clauss assay.6 Plasma tPA activity was determined by a chromogenic microtiter assay (Chromolize, Biopool). Commercially available ELISA was used for the assessment of FVIIag and ß-TG (both from Diagnostica Stago) and for tPA and PAI-1 antigen in plasma (both from Biopool). Plasma FbdP (Organon Teknika), F1+2 (Behringwerke AG), and Lp(a) (Biopool AB) were also determined with ELISA methods. Plasma vWF was assessed with an ELISA as described earlier.7 Plasma glucose was measured by the hexokinase method (Gluco-quant, Boehringer Mannheim GmbH), and serum insulin with RIA (Insi-Pr, CIS). Serum concentrations of CRP were determined by immunoturbidimetry. Samples with elevated levels (>10 mg/L) were omitted from the statistical analyses.

The intraserial analytical variations (expressed as coefficients of variation) were: blood lipids, apolipoproteins, glucose, and CRP <2%; FVIIc, FVIIa, FVIIag, fibrinogen, Lp(a), and FbdP <5%; insulin <6%; tPA and PAI-1 antigen, ß-TG, F1+2, and vWF <9%; and tPA activity <12%.

The fatty acid composition of LDL lipids was determined by gas chromatography after LDL separation by ultracentrifugation. A 50-µL LDL sample was extracted twice with chloroform:methanol (2:1), the solvent was evaporated, and the sample reconstituted in 0.5 mol/L NaOH in methanol. The fatty acids were saponified using BF3 and reconstituted in 1 mL hexane. The fatty acid composition was determined using an HP5880A gas chromatograph (Hewlett Packard) with a flame ionization detector, a Supelco SP2380 column, 30 m, 0.32 µ ID fused silica (Supelco). Aliquots of 5 µL were injected using an HP 7673 autoinjector with a flow of 10 mL/50 s and a split ratio of 1.17:10. Helium was used as a carrier gas. Fatty acids were determined by comparison with commercial standards (Nu-Chek). Results were initially expressed in percentages of total peak area and then converted to mole percent.

Dietary Assessments
Three 24-hour dietary recall interviews were conducted at weeks 0 (study entry), 3 (end of run-in), and 7 (end of intervention). Portion sizes were assessed in terms of household and photographic measures. The calculation of energy and nutrient intakes was based on the official Danish food composition table.8 Habitual consumption of fish was also assessed by a diet history interview covering the preceding 3 months.

Study compliance was assessed by a combination of records of margarine use kept by the volunteers and determinations of the n-3 VLCPUFA content of LDL lipids. The LDL n-3 VLCPUFA content is not the best plasma marker of the dietary n-3 VLCPUFA intake, but it was selected because it was available from a substudy of fish oil and LDL oxidation based on the same blood samples (to be presented separately). A significant positive association between fish intake (grams per day ), as assessed from the diet history interviews, and the DHA content of LDL before intervention was demonstrated (r=.29, P<.05).

Statistics
Fasting blood samples were compared by multivariate analysis of variance (repeated measurements) of untransformed (for Gaussian distributions) or log-transformed (if non-Gaussian) data. Individual postprandial profiles of plasma triglycerides, FVII measures, tPA activity, glucose, and serum insulin were expressed in terms of nonfasting peak and mean values. Nonparametric methods (Wilcoxon's matched-pairs signed rank test and Mann-Whitney U test) were applied to allow for the limited number of test meal participants and the non-Gaussian distribution of most postprandial variables. A value of P<.05 (two-tailed) was considered significant. A package for the personal computer (SPSS/PC+, V4.0) was used for all statistical analyses.


*    Results
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 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 *Results
down arrowDiscussion
 down arrowReferences
 
The habitual fish and n-3 VLCPUFA intake was low. On average, fish was used for sandwich topping once weekly. Fish dinners were eaten twice every month. According to the three 24-hour dietary recalls, the habitual intake of n-3 VLCPUFA from fish was minimal (median: 46 mg/d, 25th to 75th percentile: 0 to 432 mg/d). The contribution of n-3 VLCPUFA from other sources than fish (animal meat) was estimated to be <25 mg/d. The macronutrient composition of habitual diets is shown in Table 2Down.


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  		Table 2. Calculated Energy Content and Nutrient Composition of Habitual Diets According to 24-Hour Dietary Recalls at Study Entry (n=47)

The introduction of 30 g/d of SUN margarine during run-in caused an expected change in the diet. The intake of polyenes increased from 6% to 8% of energy (P=.007), the intake of monoenes from 11% to 13% of energy (P=.046), and the total fat intake from 39% to 43% of energy (P<.01). The carbohydrate content of the diet changed oppositely, from 44% to 41% of energy (P=.005). No other changes were observed. The diet did not change during the intervention period, except for the change in fatty acid composition caused by the replacement of SUN with FISH margarine in the FISH group.

Study Compliance
The participants' margarine records showed almost perfect compliance. A few volunteers reported to have omitted or forgotten 1 to 3 units of 15 g during the total study duration of 7 weeks. The LDL content of EPA increased from 0.78 (SD 0.06) to 1.51 (SD 0.08) mol % (P<.001) and of DHA from 1.95 (SD 0.09) to 2.63 (0.09) mol % (P<.001) during intervention in the FISH group. In the SUN group, EPA rose from 0.96 (SD 0.11) to 0.99 (SD 0.08) mol %, and DHA from 1.97 (SD 0.09) to 2.12 (SD 0.11) mol % (insignificant changes).

The participants were unable to differentiate between the two margarines with regard to taste, smell, color, and texture according to questionnaires filled in at the end of the study. Blinding was thus complete.

Observations After Run-in and Before Intervention
Average age, weight, body mass index, and dietary habits were similar in the FISH and SUN groups. Biochemically, they were also similar, except for FVIIa (89 versus 72 U/L, P<.05; Table 3Down).


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  		Table 3. Fasting Plasma Lipids, Apolipoproteins, and Hemostatic Variables Before and After 4 Weeks of Intervention in Two Groups Consuming Either Fish Oil–Enriched Margarine (FISH, n=23) or Conventional Sunflower Oil Margarine (SUN, n=24)

Fig 1Down shows postprandial profiles of blood coagulation FVII, plasma triglycerides, insulin, and tPA activity before intervention (n=19). All variables varied significantly postprandially. Plasma FVIIc increased from 100% (fasting) to 117% at 1600 hours. Plasma FVIIa rose dramatically from 82 to 130 U/L. Plasma FVIIag varied only slightly around fasting levels. Plasma triglycerides more than doubled, from a fasting level of 0.92 to 2.13 mmol/L at 1315 hours. Serum insulin peaked simultaneously and then started to decline. Plasma tPA activity increased from a fasting level of 0.47 IU/mL to a maximum of 0.87 IU/mL at 1430 hours.



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  		Figure 1. Postprandial profiles of plasma FVIIc, FVIIa, FVIIag, triglycerides, insulin, and tPA activity in response to high-fat test meals (M) served at 9 AM and 11 AM (n=19). Values are medians and 25th to 75th percentile ranges.

Observations After Intervention in Fasting Blood Samples
In multivariate analyses, there was no significant effect of fish oil on fasting levels of any variable (Table 3Up). Plasma HDL cholesterol and apolipoprotein A-I concentrations increased during intervention in the FISH group, but similar changes were seen also in the SUN group. Plasma triglycerides decreased significantly in the FISH group, but a similar insignificant trend was observed also in the SUN group.

Observations After Intervention: Effects on Nonfasting Samples
Fish oil had a significant effect on postprandial triglycerides (Table 4Down and Fig 2Down). In the FISH group, nonfasting triglycerides declined by 16% to 18% during intervention, whereas a 10% to 13% increase was observed in the SUN group. The decline in postprandial triglyceride concentrations attributable to the substitution of sunflower oil with fish oil was thus around 30%. The strong influence on postprandial triglycerides was not associated with concomitant effects on nonfasting FVIIa levels (Table 4Down).


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  		Table 4. Nonfasting Plasma Triglycerides, FVII, Glucose, and Serum Insulin Measured Before Intervention and the Percentage Change After Intervention in Two Groups Consuming Fish Oil–Enriched Margarine (FISH, n=10) or Conventional Sunflower Oil Margarine (SUN, n=9) for 4 weeks



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  		Figure 2. Individual postprandial peak concentrations (mmol/L, log10 scale) of plasma triglycerides after high-fat test meals consumed before and after eating a fish oil–enriched margarine (FISH, n=10) or a conventional sunflower oil margarine (SUN, n=9) for 4 weeks.

A fish oil–attributable 9% lowering of the postprandial mean FVIIag concentration was demonstrated (Table 4Up). Fish oil had a borderline significant (P=.06) effect on nonfasting insulin. There was no significant effect of fish oil on nonfasting FVIIc, the FVIIa:FVIIag ratio, tPA activity, or glucose.

Associations Between Variables
The relationship between pairs of biochemical variables was assessed in linear correlation analyses. Only associations statistically significant at a value of P<.001 before (week 3) and after intervention (week 7) were considered of true relevance. These strongly and consistently associated pairs of variables are presented in Table 5Down.


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  		Table 5. Pairs of Biochemical Variables Strongly (P<.001) and Consistently Associated in Fasting Blood Samples Collected Before and After a 4-Week Intervention Period (n=47)


*    Discussion
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 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 *Discussion
down arrowReferences
 
Whether fish and n-3 VLCPUFA protect against IHD is still debated. Very recent studies reached diverging conclusions.9 10 11 12 Any protective effect of fish appears to be achieved at low intakes (1 to 2 servings per week, corresponding to 0.5 to 1.0 g of VLCPUFA per day).13 14 In the present study, we tested whether 0.91 g/d had any effect on key components of lipid metabolism and the hemostatic system. These components are of pathogenetic importance in IHD. The only n-3 VLCPUFA effect we observed that could contribute to the putative cardioprotective effects of moderate fish consumption was a lowering of postprandial triglycerides.

The habit of consuming 30 g margarine per day was established during the run-in period of our study. As expected, it led to a change in the macronutrient composition of the overall diet. Changes were not seen during the intervention period. The use of margarine as carrier of the fish oil prevented group differences in total energy and fat intake during intervention. It may be argued that our intervention period was too short to assess the long-term impact of fish oil because steady state conditions not are reached within 4 weeks. This may be true, but on the other hand, we want to emphasize that the n-3 VLCPUFA incorporation into plasma fatty acids, including phospholipid subclasses, and platelets seems to be almost complete after 3 weeks, in particular at lower intakes.15 16 17 These aspects of metabolism are those most closely related to the IHD risk factors of our interest. In addition, dietary effects on blood lipids, FVII, and the fibrinolytic system can be demonstrated after intervention periods of only 10 to 14 days,18 19 and one long-term strictly controlled trial indicated that the early (4- to 8-week) influence does not differ from late (8 months) effects of a dietary change.20 Still, we cannot exclude that we might have had a different study outcome with a longer intervention period.

Fish oil had no significant effects on fasting plasma concentration of blood lipids and apolipoproteins A-I and B. We did see the expected decline in triglycerides and increase in HDL cholesterol,21 but similar trends were seen in the SUN group, and the changes did not differ in multivariate analyses. Postprandial triglyceride concentrations were dramatically reduced by fish oil, however. The fish oil–attributable decline came close to 30%. Changes of this magnitude were also observed in earlier trials using higher dosages of fish oil or longer treatment periods.22 23 24 25 26 According to some epidemiological observations, a lowered nonfasting triglyceride concentration may imply a reduced risk of IHD.27 28 It is debated, though, whether nonfasting triglycerides are independently related to IHD risk.29 30 The coexistence of elevated triglycerides with hypercoagulability and low HDL cholesterol levels may explain the relation.31 32 Others argue that triglyceride-rich lipoproteins and their remnants are causally related to atherogenesis.33 34 35 36 37 So far, the clinical consequences of lowered nonfasting triglycerides remain controversial.

How are nonfasting triglycerides lowered by fish oil? One possibility is that fish oil enhances the clearance of chylomicrons by hepatic and endothelial lipases. This effect could be explained by a reduced competition for the lipolytic enzymes due to an attenuated hepatic output of VLDLs or by an increased specific activity of lipoprotein lipase caused by an altered fatty acid composition of the cellular membranes in which the enzyme is embedded.21 24 25 38 A decreased chylomicron entry into the plasma pool might also explain the findings, and this possibility cannot be ruled out.39 The stable body weights of the participants consuming FISH argues against a fish oil–induced reduction in the intestinal fat absorption, which could also theoretically explain the lowering of nonfasting triglycerides.

Blood coagulation FVII, fibrinogen (both predictors of IHD in epidemiological studies),40 41 42 and F1+2 (a marker of coagulation activation) were all unaffected by fish oil when measured in the fasting state. In fact, the only significant finding within the blood coagulation system was a lowering of nonfasting FVIIag concentrations by fish oil. The latter effect was not sufficiently strong to affect FVII clotting activities and may not have any physiological impact. Our present findings confirm earlier fish diet and fish oil supplementation studies reporting FVII clotting activity and fibrinogen not to be affected.43 44 45 It is unlikely that any effect of fish consumption on IHD is mediated via modifications of these hemostatic risk markers.

The mechanisms behind postprandial FVII activation have been studied by different groups.5 46 47 48 49 50 51 The nonfasting triglyceride concentration was proposed as the essential determinant, except for individuals with lipoprotein lipase deficiency.48 49 This hypothesis was based on the consistent observation of higher plasma triglycerides and accentuated FVII activation after high-fat meals. We found no fixed links between triglycerides and FVII activation in two earlier studies, however.5 46 The present study confirmed that high-fat meals lead to extensive FVII activation (FVIIa increased almost 50% from fasting levels; Fig 1Up) but also showed that fish oil may induce significant changes in nonfasting triglyceride profiles without concomitant effects on FVIIa. Another recent study showed that the consumption of medium-chained fatty acids does not lead to FVII activation.51 These fatty acids are transported to the liver via the portal vein and thus bypass the lipoprotein route of distribution. Therefore, FVII activation seems to be determined rather by the mass of dietary fat processed by the endothelial lipoprotein lipase than by the triglyceride concentration. A high flux of lipolytic products of triglyceride-rich lipoproteins may thus be a key factor in FVII activation. We suggest that a high flux may lead to an increase in the expression of tissue factor on the surface of monocytes and/or endothelial cells and promote FVII activation in that way.52 According to an earlier hypothesis, micelles of free fatty acids formed during lipolysis cause factor XII activation and subsequent FVII activation by activated factor XII.49 A recent study showed that dietary fat also causes FVII activation in factor XII–deficient patients, however.53 At present, it therefore seems unlikely that factor XII contributes to the link from high-fat meals to FVII activation.

The consumption of fish diets and fish oil supplements equivalent to a daily dosage of 1.8 g n-3 VLCPUFA or more is associated with a rise in PAI levels and an inhibition of the fibrinolytic system.18 44 45 54 55 56 This prothrombotic effect was not seen with the lower n-3 VLCPUFA intake of the present trial. The absent influence on FbdP (a marker of ongoing fibrinolysis) and Lp(a) also suggests that endogenous fibrinolysis was unaffected.

Several trials have investigated the effect of fish or fish oil on platelet aggregation.16 45 55 57 58 59 60 Such studies have had diverging results which may be due to analytical difficulties. Plasma ß-TG, a protein released from platelet granules during activation, may be a more reliable indicator of in vivo platelet activation. The present study showed no effect on ß-TG concentrations in plasma and thus gives no support for an antithrombotic effect of moderate fish oil consumption on platelet function.

Strong and consistent associations between some of the analyzed variables were demonstrated. In agreement with a recent Finnish study, apolipoprotein B concentrations correlated positively with total cholesterol, triglycerides, and FVIIc.61 The observed inverse relationship between tPA antigen and tPA activity is explained by the well-known augmented fibrinolytic inhibition (high PAI-1 levels) at high plasma concentrations of tPA antigen.62 These associations help to explain why tPA antigen concentrations are positively associated with IHD risk.62 63

In conclusion, this study showed that the consumption for 4 weeks of 0.91 g n-3 VLCPUFA per day lowers nonfasting triglycerides in healthy middle-aged men. Other more critical aspects of lipid metabolism and a wide range of thrombogenic factors were not affected. A lowering of postprandial triglycerides was thus the only n-3 VLCPUFA effect that could contribute to primary prevention of IHD, as assessed by currently measurable and well-established lipid and hemostatic risk markers. It is possible that the putative benefit of moderate fish consumption in primary prevention of IHD comes rather from fish replacing foods that are atherogenic and prothrombotic than from specific n-3 VLCPUFA effects. The impact of n-3 VLCPUFA in secondary prevention of IHD may be very different and cannot be determined from the present study.


*    Selected Abbreviations and Acronyms
 
CRP = C-reactive protein
ELISA = enzyme-linked immunosorbent assay
F1+2 = prothrombin fragment 1+2
FbdP = fibrin degradation products
FVII = factor VII
FVIIa = activated FVII
FVIIag = FVII antigen
FVIIc = FVII coagulant activity
IHD = ischemic heart disease
Lp(a) = lipoprotein(a)
PAI-1 = plasminogen activator inhibitor type 1
ß-TG = ß-thromboglobulin
tPA = tissue-type plasminogen activator
VLCPUFA = very-long-chain n-3 polyunsaturated fatty acids
vWF = von Willebrand factor


*    Acknowledgments
 
This study was supported by a grant from MD Foods, Denmark. PhD student Nina Skall Sørensen and her supervisor, Associate Prof Carl-Erik Høy, the Danish Technical University, are thanked for performing the fatty acid composition analyses of LDL particles. The study technicians Klara Jørgensen, Johannes Sidelmann, Mette Toft, and Katrine Overgaard Sørensen were, as always, excellent collaborators. The contribution of dietitian Lena Theilgaard Andersen was important and much appreciated.

Received November 5, 1996; accepted April 10, 1997.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 up arrowDiscussion
 *References
 

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