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Cardiovascular Disease

Read on for detailed information about how various oils contribute to your cardiovascular health. If you'd like to read research on a specific product, click on the product name below:
Flaxseed Oil
Flaxseed
Evening Primrose Oil
Borage

Flaxseed Oil
Alpha-linolenic acid (ALA), the main fatty acid constituent in flaxseed oil, is the precursor to eicosapentaenoic acid (EPA) and docasahexaenoic acid (DHA), both of whose beneficial effects in cardiovascular disease have been well documented. These effects include reduction of plasma triglycerides and VLDL cholesterol (1,2,3,4) protection against coronary heart disease (CHD) and acute myocardial infarction (MI) (5,6,7) reduction of hypertension (8,9,10, 11) and improvement in vascular response and blood-flow(2, 11).

As such, it has been hypothesized that through its conversion to EPA and DHA, ALA itself may also be of benefit in the treatment and prevention of heart disease. Additionally, some researchers hypothesize that ALA in its own right may be an anti-thrombotic and anti-arrhythmic agent (12, 13, 14) therefore reducing the risk of blood clotting and arrhyhtmias (irregular heart rhythm), respectively. The mechanisms by which these effects may occur have not been confirmed.

A number of epidemiological and clinical observational trials have investigated the effects of increased ALA consumption on the incidence of MI and CHD. The incidences of CHD in Japanese and Cretan populations are among the lowest in the world, and these populations also consume comparatively high levels of ALA in their normal diets (14. Some observational cohort studies have shown correlations between higher intakes of ALA and reduced risk of fatal CHD in women (with a stronger correlation found for those also having higher vitamin E intake) (14) and non-fatal MI in men(15). Alternatively, other observational cohort studies (16, 17) have not found any significant correlation between ALA intake/serum concentration and coronary event development.

Dietary interventional trials involving ALA-rich Mediterranean diets have reported protective effects against primary and secondary prevention of CHD (13, 18). Although these interventional were multi-factorial and may have featured a variety of confounding dietary variables, the extended follow up (19) of one of these studies (13) noted that ALA was the only plasma fatty acid measured that had an association with reduced risk of non-fatal MI or cardiac death.

Studies of the effects of flaxseed oil supplementation on serum lipid profiles have yielded inconsistent results. Two randomized controlled trials, one investigating flaxseed oil (20) and the other investigating increased dietary ALA, (18) have shown significant improvements in serum triglyceride and cholesterol parameters. Another non-controlled trial reported that ALA had approximately the same reductive effect on total serum cholesterol as oleic and linoleic acid (21). However, some controlled trials have not reproduced the triglyceride-lowering effects of fish oil using flaxseed oil (22, 23) or non-flaxseed oil ALA supplementation (24, 25). In general, improvements in serum cholesterol generally have not been demonstrated (13, 22, 23, 25, 26).

Subtle improvements in blood pressure (18, 20, 27) have been associated with increased dietary/serum ALA, although not all studies confirm these findings(13). There have been reported positive correlations between increased plasma ALA levels and endothelial-dependent blood vessel response and blood vessel function in general, both of which are known to be compromised in early development of atherosclerosis (28). Arterial compliance has been shown to improve as a result of flaxseed oil treatment ([jump footnote 23:23]), and reduced blood vessel thickening in the internal carotid artery has been associated with increased intake of linolenic acid (29).

It is important to consider that some of the results may not have clearly assessed the potential benefits of ALA since many of the sources of ALA investigated in these studies also provided significant amounts of potentially confounding substances, such as the trans-fatty acids found in partially-hydrogenated oils (12, 17), which increase risk for cardiovascular disease.

Flaxseed
Increased risk of cardiovascular disease, specifically coronary heart disease, is by far the greatest menopause-related issue in terms of mortality (30). Currently, there is limited clinical research focusing specifically on the effects of flaxseed consumption on cardiovascular disease in postmenopausal women. One randomized, controlled clinical trial involving postmenopausal women showed that 40 grams per day of ground flaxseed for 3 months was associated with significant reductions in total cholesterol, non-HDL cholesterol, and apolipoprotein-B (a cardiovascular disease risk factor), while levels of LDL cholesterol and serum triglycerides remained unchanged (31). However, another randomized clinical trial compared the effects of the same dosage of ground flaxseed with those of standard hormone replacement therapy (HRT) treatment in postmenopausal women, and found that, while HRT improved several lipid parameters over the course of 2 months, flaxseed had no effect on serum cholesterol or triglyceride levels over the same time period (32). Although these results do not provide a clear understanding of the cardiovascular effects of flaxseed consumption in postmenopausal women, flaxseed has been reported to have lipid-lowering effects in other population groups both with and without hyperlipidemia (33, 34, 35).

The potential mechanisms by which flaxseed may have an effect upon cardiovascular disease are at least threefold:
  • The high content of alpha-linolenic acid (ALA) in flaxseed may have lipid-modifying and anti-platelet aggregating effects on its own or via its metabolites, eicosapentaenoic acid (EPA) and docasahexaenoic acid (DHA).
  • The large amounts of dietary fiber in flaxseed may have the ability to lower blood lipids, potentially through the ability of fiber to increase cholesterol excretion (30, 31, 32).
    [list:The plant lignans in flaxseeds are known to be potent antioxidants, with the lignan secoisolariciresinol diglycoside (SDG) suggested to have even greater antioxidant activity than vitamin E (33). Therefore, plant lignans may be able to help prevent atherosclerotic plaque formation, which involves oxidation of lipids in the blood. In addition, flaxseed lignans may benefit cardiovascular disease patients by altering the activity of an enzyme, cholesterol 7-hydroxylase, which is involved in the metabolism of cholesterol.

    • Several clinical trials have investigated the effect of flaxseed supplementation on lipid levels. In general, a daily intake of 20-50 grams of ground flaxseed has led to significant reductions in total cholesterol (31, 32, 34, 35) and LDL-cholesterol (31, 34, 35); two additional studies showed benefit but the reductions were found to only occur over a short period of time (30, 36). Based upon findings from clinical trials to date, flaxseeds do not seem to have any significant effect on HDL-cholesterol and serum triglycerides (30, 31, 32, 34, 35). Reductions in both apolipoprotein A1 (Apo-A1), a cardioprotective factor, and apolipoprotein B (Apo-B), a risk factor for cardiovascular health, have been noted in two studies (31, 32) with the reduction of Apo-B outweighing that of Apo-A1 (thus a theoretically cardioprotective effect) in one of these trials (32). All of the above results were similar in healthy young patients and older hyperlipidemic patients, with one study (31) also reporting no major differences between effects in men and women. It is not clear whether the observed changes in lipid levels are attributable to fiber, ALA, lignans, or a combination of factors.

    Although an animal study reported that flaxseed supplementation led to a reduction in the number and distribution of atherosclerotic plaques as well as a reduced oxidative activity of inflammatory cells (37), clinical studies in humans have suggested that flaxseed supplementation may be associated with increased oxidative activity (30, 31, 34). More research needs to be done in this area in order to clarify whether flaxseed contributes to lipid oxidation and, if so, what impact this actually has on health, and whether supplementation with an antioxidant, such as vitamin E, can mitigate any pro-oxidant effects, if they exist.

    Evening Primrose Oil
    There are several potential effects of evening primrose oil (EPO) in the treatment of various cardiovascular conditions. Human and animal studies have been conducted to test the efficacy and mechanisms of the effect of EPO on cholesterol and other lipid modification, vascular reactivity, atherogenesis, coronary heart disease, hypertension and hemostasis (blood clotting). The theoretical underpinnings of these trials have been largely related to the fact that prostaglandin E1 (PGE1) and prostacyclin (PGI2), two of the ultimate metabolites of gamma-linolenic acid (GLA), which is one of the main ingredients of EPO, have vasodilatory, anti-platelet aggregatory and cholesterol reducing properties.

    Borage Oil
    Borage oil contains a relatively high concentration of gamma-linolenic acid (GLA), typically in the range of 22-23% by weight.1, 2 GLA-concentrated ingredients, notably evening primrose oil, have been tested as a modifier of several cardiovascular disease parameters, including serum lipids, 3, 4, 5, 6, 7 hypertension8, 9, 10 and platelet aggregation.4, 11 The theoretical underpinnings of these trials have been largely related to the fact that two of the ultimate metobolites of GLA, prostaglandin E1 (PGE1) and prostacyclin (PGI2), have vasodilatory, anti-platelet aggregatory and cholesterol reducing properties. Theoretically, these GLA-related mechanisms are as applicable to borage oil and other sources of GLA as they are to evening primrose oil.

    The information presented here is for educational purposes only and is not intended as curative or prescriptive advice.

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