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

January 1, 2009 Human Health and Nutrition Data 0 Comments

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

Year: 2009
Authors: Pan, A. Yu, D. Demark-Wahnefried, W. Franco, O.H. Lin, X.
Publication Name: Am. J. Clin. Nutr.
Publication Details: Volume 90; Pages 288 – 297.


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. We aimed to identify and quantify the effectiveness of flaxseed and its derivatives on blood lipid profiles. 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 Attempts also were made to access unpublished data.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. Twenty-eight studies were included. Flaxseed interventions reduced total and LDL cholesterol by 0.10 mmol/L (95% CI: 20.20, 0.00 mmol/L) and 0.08 mmol/L (95% CI: 20.16, 0.00
mmol/L), respectively; significant reductions were observed with whole flaxseed ( 20.21 and 20.16 mmol/L, respectively) and lignan (20.28 and 20.16 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. 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. (Authors abstract)
Previous animal studies suggest that flaxseed reduces both total and LDL cholesterol. Flaxseed lignans also have cholesterol-lowering effect and could regress the atherosclerotic process. The findings from many clinical trials on flaxseed are inconsistent, and the discrepancies could be attributed to small sample size, insufficient study duration, variation in study designs, and diversity of the test product. The objective of this meta-analysis was to evaluate whether administration of flaxseed or its derivatives could improve blood lipids (total, LDL, and HDL cholesterol and triglycerides). Overall, flaxseed supplementation was associated with a decrease in blood total and LDL-cholesterol concentrations but did not substantially affect HDL cholesterol and triglycerides. These changes varied substantially depending on the treatment form of flaxseed, quality of the study, sex, and initial lipid profile of the subjects. Whole flaxseed interventions were associated with significant reductions in total and LDL cholesterol, whereas flaxseed oil interventions were not. It appears that initial cholesterol profiles exert a powerful moderating effect on changes in lipid concentrations: the beneficial effects of flaxseed and its derivatives were only observed among those with relatively high initial cholesterol concentrations.  The cholesterol-lowering effect of flaxseed and its products was more remarkable in women than in men. This difference was more striking in postmenopausal women, who tended to experience increased total and LDL-cholesterol concentrations as a result of estrogen decline. No significant effects of flaxseed or its derivatives on HDL cholesterol and triglycerides was noted. The effects of flaxseed on dyslipidemia appear to be clinically significant. However, the effects of flaxseed on lipid profiles are not uniform because of the substantial heterogeneity among individual studies, ie, the studies were conducted in a variety of populations and had different study designs, methods, and criteria. The cholesterol-lowering effects were related to the type of intervention, study quality, sex, and initial lipid profiles. The authors suggest that flaxseed consumption may be a worthwhile dietary approach for preventing hypercholesterolemia, particularly in specific patient subgroups.  Further studies are needed with large sample sizes, adequate durations, and solid study designs to investigate the effectiveness of flaxseed supplementation on cardiometabolic risk factors other than blood lipids, on various chronic diseases (eg, the metabolic syndrome and diabetes), and ultimately on CVD-related morbidity and mortality. (Editors comments)

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