Effects of Flaxseed on Lipids and Bone Metabolism in Postmenopause

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Reviewed: Lucas E, Wild R, Hammond L, et al. Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women. Journal of Clinical Endocrinology & Metabolism 2002;87(4):1527-1532.

This three-month study examined the effects of flaxseed supplementation on lipids and bone metabolism in post-menopausal women. Flaxseed (Linum usitatissimum L., Linaceae) is the richest known food source of lignans, a type of phytoestrogen, and is being incorporated into human diets because of its health benefits. It has been reported that phytoestrogens reduce serum cholesterol. Lignans may also have estrogenic and/or anti-estrogenic and antioxidant properties. Due to the structural similarities between lignans and estrogen, the authors postulate that flaxseed may play a role in maintaining skeletal health. Estrogen is efficacious at preventing bone loss.

This randomized, controlled, double-blind, parallel trial is based on 36 postmenopausal women (less than 65 years old), who were not taking conventional hormone replacement therapy or any prescription medications known to influence lipid or bone metabolism. Subjects consumed 40 g of either ground whole flaxseed or wheat-based control regimen daily for 3 months. All subjects were provided with 1,000 mg elemental calcium plus 400 IU vitamin D for daily consumption. Food questionnaires and physical and gynecological examinations were conducted at the beginning and upon completion of the study. Serum total cholesterol and triglyceride concentrations, levels of sex hormones, and markers of bone metabolism were assessed.

Both groups had similar dietary intakes before and after the study. Consumption of flaxseed, but not wheat-based regimen, for 3 months resulted in a significant decrease (6%) in both serum total and non-HDL cholesterol concentrations. Flaxseed, but not wheat-based regimen, reduced serum levels of apolipoprotein A-1 and apolipoprotein B — markers of heart disease risk. This finding suggests a cardioprotective effect. There were no significant changes in measures of bone metabolism. Neither flaxseed nor wheat-based regimen produced estrogenic effects.

In this study, LDL-cholesterol was lowered by 4.7%, whereas in a previous study by the same authors, it was reduced by 14.7%.[ 1] The authors believe that feeding subjects whole ground flaxseed, rather than incorporating it into baked goods as was done in the previous trial, may have contributed to the difference. It is not clear whether all constituents of flaxseed that influence lipid metabolism are bioavailable when flaxseed is consumed in the raw form. However, this requires further investigation.

The authors conclude that the findings of this study suggest that flaxseed consumption by postmenopausal women is effective in reducing known risk factors of coronary heart disease. Flaxseed did not exert any estrogenic properties and had no role in maintaining skeletal health.

However, an HerbalGram reviewer noted that the high dropout rate in this trial may invalidate the authors conclusions. The trial started with 58 women with a greater number of flax subjects than wheat subjects 920 vs. 16, respectively) completing the study. Thus, with 22 women (38% of the initial group) not completing the study, there is more than a 33% dropout rate. Usually, in the evaluation of clinical trials, a dropout rate of over one-third invalidates the outcomes.

For more on the actions and potential benefits of flaxseed, see the extensive monograph in The ABC Clinical Guide to Herbs.[ 2]
References:

1. Arjmandi BH, Khan DA, Juma S, Drum ML, Venkaresh S, Sohn E, Wei L, Derman R. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res 1998;18:1203-14.

2. Blumenthal M, Hall T, Goldberg A, Kunz T, Dinda K, Brinckmann J, et al., editors. The ABC Clinical Guide to Herbs. Austin, TX: American Botanical Council; 2003:143-52.

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By Heather S. Oliff, PhD

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