Elsevier

The Lancet

Volume 361, Issue 9356, 8 February 2003, Pages 477-485
The Lancet

Mechanisms of Disease
Association of n-3 polyunsaturated fatty acids with stability of atherosclerotic plaques: a randomised controlled trial

https://doi.org/10.1016/S0140-6736(03)12468-3Get rights and content

Summary

Background

N-3 polyunsaturated fatty acids (PUFAs) from oily fish protect against death from cardiovascular disease. We aimed to assess the hypothesis that incorporation of n-3 and n-6 PUFAs into advanced atherosclerotic plaques increases and decreases plaque stability, respectively.

Methods

We did a randomised controlled trial of patients awaiting carotid endarterectomy. We randomly allocated patients control, sunflower oil (n-6), or fish-oil (n-3) capsules until surgery. Primary outcome was plaque morphology indicative of stability or instability, and outcome measures were concentrations of EPA, DHA, and linoleic acid in carotid plaques; plaque morphology; and presence of macrophages in plaques. Analysis was per protocol.

Findings

188 patients were enrolled and randomised; 18 withdrew and eight were excluded. Duration of oil treatment was 7–189 days (median 42) and did not differ between groups. The proportions of EPA and DHA were higher in carotid plaque fractions in patients receiving fish oil compared with those receiving control (absolute difference 0·5 [95% CI 0·3–0·7], 0·4 [0·1–0·6], and 0·2 [0·1–0·4] g/100 g total fatty acids for EPA; and 0·3 [0·0–0·8], 0·4 [0·1–0·7], and 0·3 [0·1–0·6] g/100 g total fatty acids for DHA; in plaque phospholipids, cholesteryl esters, and triacylglycerols, respectively). Sunflower oil had little effect on the fatty acid composition of lipid fractions. Fewer plaques from patients being treated with fish oil had thin fibrous caps and signs of inflammation and more plaques had thick fibrous caps and no signs of inflammation, compared with plaques in patients in the control and sunflower oil groups (odds ratio 0·52 [95% CI 0·24–0·89] and 1·19 [1·02–1·57] vs control; 0·49 [0·23–0·90] and 1·16 [1·01–1·53] vs sunflower oil). The number of macrophages in plaques from patients receiving fish oil was lower than in the other two groups. Carotid plaque morphology and infiltration by macrophages did not differ between control and sunflower oil groups.

Interpretation

Atherosclerotic plaques readily incorporate n-3 PUFAs from fish-oil supplementation, inducing changes that can enhance stability of atherosclerotic plaques. By contrast, increased consumption of n-6 PUFAs does not affect carotid plaque fatty-acid composition or stability over the time course studied here. Stability of plaques could explain reductions in non-fatal and fatal cardiovascular events associated with increased n-3 PUFA intake.

Introduction

Consumption of long-chain n-3 polyunsaturated fatty acids (PUFAs)—found in oily fish and fish oils—protects against cardiovascular disease in people in developed countries.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 Long-chain n-3 PUFAs reduce fasting plasma triacylglycerol concentrations and decrease post-prandial lipaemic responses.12, 13 Dietary fish oil has been shown to reduce atherosclerosis in animals,14, 15, 16 which might be attributable to lipid-lowering, a fall in growth-factor production,17, 18 decreased inflammation,19 or a combination of these effects. Secondary prevention studies, in which long-chain n-3 PUFAs were given to patients who had had a myocardial infarction, showed significant benefit on cardiovascular outcomes.20, 21, 22 N-3 PUFAs are especially effective in reduction of sudden death,6, 7, 8, 20, 21, 22 which happens without great lipid-lowering.22 This effect might be attributable to antithrombotic and antiarrhythmic actions of these fatty acids,12, 13, 23 although n-3 PUFAs could contribute to stabilisation of atherosclerotic plaques through their anti-inflammatory actions.19 By contrast, the n-6 PUFA linoleic acid, which is present in vegetable oils such as sunflower oil, has been suggested to promote inflammation.24 If so, then increased intake of linoleic acid might contribute to plaque instability.

If PUFAs are to affect plaque stability then they must first be incorporated into the plaque. Results of a study by Rapp and colleagues25 showed that this incorporation can take place for n-3 PUFAs. Patients waiting to undergo endarterectomy consumed fish oil for a period before surgery, and concentrations of n-3 PUFAs (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) in plaques removed at surgery were much higher than in those removed from controls.25 However, Rapp gave patients a very high dose of fish oil: 48–64 g/day, providing 16–21 g EPA and DHA per day. By comparison, habitual consumption of long-chain n-3 PUFAs in most Western diets is less than 0·3 g/day,13 and secondary prevention studies show protective effects with less than or equal to 1·8 g EPA and DHA per day.20, 21, 22 Furthermore, the study by Rapp and colleagues25 was not placebo-controlled or masked, included a heterogeneous group of atherosclerotic plaques (carotid, femoral, aorta, iliac) from 11 patients, and provided no structural details of plaques.

We postulated that consumption of fish oil providing a modest dose of n-3 PUFAs would result in incorporation of EPA and DHA into LDL and atherosclerotic-plaque lipid fractions and therefore in improved atherosclerotic-plaque stability, shown by the degree of macrophage infiltration and by plaque morphology. Further, we postulated that increased intake of sunflower oil would result in incorporation of the n-6 PUFA linoleic acid into LDL and atherosclerotic-plaque lipids and therefore in reduced atherosclerotic-plaque stability, also shown by degree of macrophage infiltration and by plaque morphology. Therefore, we aimed to assess dietary intervention with sunflower and fish oils in patients waiting to undergo carotid endarterectomy.

Section snippets

Patients

Between May, 1997, and December, 1999, we undertook a double-blind, randomised controlled trial in all patients waiting to undergo carotid endarterectomy at Southampton University Hospitals NHS Trust. We enrolled all patients who agreed to participate. Permission for all procedures entailing patients was obtained from the Southampton and South West Hampshire Research Ethics Committee, and all patients gave written informed consent.

Procedures

We randomly allocated patients, in a double-blind manner, to

Patients' characteristics

We enrolled 188 patients to the study. 18 of these withdrew, 13 for clinical reasons (too ill for surgery [n=3]; had surgery elsewhere [1]; death [1]; repeat doppler normal so no need for surgery [3]; refused to have surgery [1]; vessel occlusion [1]; missing operation [1]; developed leg pain ascribed [by patient] to capsules [1]; developed nausea and diarrhoea ascribed [by patient] to capsules [1]) and five because they could not adhere to the study protocol (figure 1). A further eight

Discussion

Supplementation of the diet of patients with sunflower oil, providing 3·6 g linoleic acid per day, had very little effect on primary outcomes measured, probably because these patients were already consuming a substantial quantity of linoleic acid in their diet; this intake accords with that reported for adults in the UK.12, 13 Our observations suggest that increasing linoleic acid intake by up to 40% in patients with advanced carotid atherosclerosis and consuming typical amounts of this fatty

GLOSSARY

fatty-acid composition
A description of the absolute or relative content of different fatty acids present in a particular biological sample.
immunohistochemical staining
A laboratory technique whereby antigens can be visualised in sectioned tissue by exposure to antibodies and subsequent development of colour due to a series of chemical reactions.
plaque morphology
A description of the gross microscopic appearance of a cross-section of an atherosclerotic plaque. The classification of plaque

References (35)

  • CM Albert et al.

    Blood levels of long-chain n-3 fatty acids and risk of sudden death

    N Engl J Med

    (2002)
  • DS Siscovick et al.

    Dietary intake and cell membrane levels of long-chain n-3 polyunsaturated fatty acids and the risk of primary cardiac arrest

    JAMA

    (1995)
  • A Tavani et al.

    N-3 polyunsaturated fatty acids, fish, and nonfatal acute myocardial infarction

    Circulation

    (2001)
  • JI Pedersen et al.

    Adipose tissue fatty acids and risk of myocardial infarction: a case-control study

    Eur J Clin Nutr

    (2000)
  • British Nutrition Foundation

    Unsaturated fatty acids: nutritional and physiological significance—task force report

    (1992)
  • British Nutrition Foundation

    Briefing Paper: N-3 fatty acids and health

    (1999)
  • BH Weiner et al.

    Inhibition of atherosclerosis by cod liver oil in a hyperlipidaemic swine model

    N Engl J Med

    (1986)
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