Flaxseed Reduces Total and LDL Cholesterol Concentrations in Native American Postmenopausal Women

The cardiovascular effects of flaxseed and its omega-3 fatty acid, alpha-linolenic acid

Preventing the occurrence of cardiovascular disease (CVD) with nutritional interventions is a therapeutic strategy that may warrant greater research attention. The increased use of omega (ω)-3 fatty acids is a powerful example of one such nutritional strategy that may produce significant cardiovascular benefits. Marine food products have provided the traditional dietary sources of ω-3 fatty acids. Flaxseed is an alternative to marine products. It is one of the richest sources of the plant-based ω-3 fatty acid, alpha-linolenic acid (ALA). Based on the results of clinical trials, epidemiological investigations and experimental studies, ingestion of ALA has been suggested to have a positive impact on CVD. Because of its high ALA content, the use of flaxseed has been advocated to combat CVD. The purpose of the present review was to identify the known cardiovascular effects of flaxseed and ALA and, just as importantly, what is presently unknown.

Flaxseed lignan lowers blood cholesterol and decreases liver disease risk factors in moderately hypercholesterolemic men

The effects of flaxseed lignan (secoisolariciresinol diglucoside [SDG]) intake on hypercholesterolemia and liver disease risk factors in moderately hypercholesterolemic men were investigated. In a previous study, we reported that SDG attenuates high-fat, diet-induced hypercholesterolemia in mice. Here, we report a double-blinded, randomized, and placebo-controlled study in moderately hypercholesterolemic men in which we investigated the hypothesis that oral administration of SDG (20 or 100 mg) would decrease the level of blood cholesterol and liver disease risk factors induced by hypercholesterolemia in humans. Thirty men with total cholesterol levels of 4.65 to 6.21 mmol/L (180-240 mg/dL) were randomly assigned to 3 groups; 2 groups received flaxseed lignan capsules (SDG, 20 or 100 mg/d) and the other received placebo capsules for 12 weeks. We found that, compared to the subjects who received placebo, those who received 100 mg of SDG exhibited a significant reduction in the ratio of low-density lipoprotein/high-density lipoprotein cholesterol at baseline (P < .05) and at week 12 (P < .05). In addition, in SDG-treated subjects, we also observed a significant percentage decrease in the levels of glutamic pyruvic transaminase and gamma-glutamyl transpeptidase relative to the levels at baseline (P < .01) and a significant percentage decrease in the level of gamma-glutamyl transpeptidase relative to the placebo-treated group (P < .05). These results suggest that daily administration of 100 mg SDG can be effective at reducing blood level of cholesterol and hepatic diseases risk in moderately hypercholesterolemic men.

What should medical practitioners know about the role of alternative medicines in cardiovascular disease management?

Alternative medications as a term call up many different meanings, significance, and perceptions to various medical practitioners. Some are good; others are bad. A wide range of alternative medications with relevance or connection to cardiovascular (CV) disease have been considered. While many are worthless, others have definite benefit, and at least one, chelation therapy, is associated with definite harm, significant risk, no benefit, and enrichment of the practitioners who prescribe it. The issues concerning alternative therapies will likely never be studied with randomized clinical trials due to the lack of a profit motive on the part of pharmaceutical companies--only rarely do other institutions, such as the National Institutes of Health, support medicinal studies. Basic knowledge of alternative therapies is essential for the CV specialist and other practicing physicians and other practitioners, since at least a few of their patients will take these medications regardless of medical advice. The result is that a number of these alternative medications will then interact with conventional CV medications, many times unfavorably.

Experimental and clinical research findings on the cardiovascular benefits of consuming flaxseed

Functional foods and nutraceuticals are becoming popular alternatives to pharmacological treatments by providing health benefits and (or) reducing the risk of chronic diseases. Flaxseed is a rich source of 3 components with demonstrated cardioprotective effects: the omega-3 fatty acid α-linolenic acid (ALA), dietary fibre, and phytoestrogen lignans. Multiple clinical dietary intervention trials report that consuming flaxseed daily can modestly reduce circulating total cholesterol (TC) by 6%–11% and low-density lipoprotein (LDL) cholesterol by 9%–18% in normolipemic humans and by 5%–17% for TC and 4%–10% for LDL cholesterol in hypercholesterolemic patients, as well as lower various markers associated with atherosclerotic cardiovascular disease in humans. Evidence to date suggests that the dietary fibre and (or) lignan content of flaxseed provides the hypocholesterolemic action. The omega-3 ALA found in the flaxseed oil fraction also contributes to the antiatherogenic effects of flaxseed via anti-inflammatory and antiproliferative mechanisms. Dietary flaxseed may also protect against ischemic heart disease by improving vascular relaxation responses and by inhibiting the incidence of ventricular fibrillation.

Meta-analysis of the effects of flaxseed interventions on blood lipids

BACKGROUND

Several clinical trials have investigated the effects of flaxseed and flaxseed-derived products (flaxseed oil or lignans) on blood lipids; however, the findings have been inconsistent.

OBJECTIVE

We aimed to identify and quantify the effectiveness of flaxseed and its derivatives on blood lipid profiles.

DESIGN

A comprehensive literature search was performed on the basis of English reports of randomized controlled trials of flaxseed or its derivatives on lipid profiles in adults, which were published from January 1990 to October 2008. Attempts also were made to access unpublished data. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted.

RESULTS

Twenty-eight studies were included. Flaxseed interventions reduced total and LDL cholesterol by 0.10 mmol/L (95% CI: -0.20, 0.00 mmol/L) and 0.08 mmol/L (95% CI: -0.16, 0.00 mmol/L), respectively; significant reductions were observed with whole flaxseed (-0.21 and -0.16 mmol/L, respectively) and lignan (-0.28 and -0.16 mmol/L, respectively) supplements but not with flaxseed oil. The cholesterol-lowering effects were more apparent in females (particularly postmenopausal women), individuals with high initial cholesterol concentrations, and studies with higher Jadad scores. No significant changes were found in the concentrations of HDL cholesterol and triglycerides.

CONCLUSIONS

Flaxseed significantly reduced circulating total and LDL-cholesterol concentrations, but the changes were dependent on the type of intervention, sex, and initial lipid profiles of the subjects. Further studies are needed to determine the efficiency of flaxseed on lipid profiles in men and premenopausal women and to explore its potential benefits on other cardiometabolic risk factors and prevention of cardiovascular disease.