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Meta-Analysis
. 2009 Aug;90(2):288-97.
doi: 10.3945/ajcn.2009.27469. Epub 2009 Jun 10.

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

An Pan  1 , Danxia Yu, Wendy Demark-Wahnefried, Oscar H Franco, Xu Lin
Affiliations
Meta-Analysis

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

An Pan et al. Am J Clin Nutr. 2009 Aug.

Abstract

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 Attempts also were made to access unpublished data.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.

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Figures

FIGURE 1
FIGURE 1
Review flow diagram according to the Quality of Reporting of Meta-analyses (QUOROM) statement.
FIGURE 2
FIGURE 2
Net changes (95% CI) in total cholesterol associated with flaxseed intervention expressed as the change during the intervention with flaxseed or its derivatives minus the change during the control regimens. WMD, weighted mean difference; Random, random-effects model. The horizontal lines denote the 95% CIs, some of which extend beyond the limits of the scales. The square represents the point estimate of each study. The diamond represents the overall pooled estimate of the treatment effect. Overall, total cholesterol decreased by 0.10 mmol/L (95% CI: −0.20, 0.00 mmol/L; P = 0.06) in the intervention groups compared with the control arms.
FIGURE 3
FIGURE 3
Net changes (95% CI) in LDL cholesterol associated with flaxseed intervention expressed as the change during the intervention with flaxseed or its derivatives minus the change during the control regimens. WMD, weighted mean difference; Random, random-effects model. The horizontal lines denote the 95% CIs, some of which extend beyond the limits of the scales. The square represents the point estimate of each study. The diamond represents the overall pooled estimate of the treatment effect. Overall, LDL cholesterol decreased by 0.08 mmol/L (95% CI: −0.16, 0.00 mmol/L; P = 0.04) in the intervention groups compared with the control arms.
FIGURE 4
FIGURE 4
Net changes (95% CI) in HDL cholesterol associated with flaxseed intervention expressed as the change during the intervention with flaxseed or its derivatives minus the change during the control regimens. WMD, weighted mean difference; Fixed, fixed-effect model. The horizontal lines denote the 95% CIs, some of which extend beyond the limits of the scales. The square represents the point estimate of each study. The diamond represents the overall pooled estimate of the treatment effect. Overall, no significant effect of flaxseed intervention on HDL cholesterol was found (−0.02 mmol/L; 95% CI: −0.04, 0.00 mmol/L; P = 0.13).
FIGURE 5
FIGURE 5
Net changes (95% CI) in triglycerides associated with flaxseed intervention expressed as the change during the intervention with flaxseed or its derivatives minus the change during the control regimens. WMD, weighted mean difference; Fixed, fixed-effect model. The horizontal lines denote the 95% CIs. The square represents the point estimate of each study. The diamond represents the overall pooled estimate of the treatment effect. Overall, no significant effect of flaxseed intervention on triglycerides was found (−0.03 mmol/L; 95% CI: −0.08, 0.02 mmol/L; P = 0.29).
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