Key Findings:
The ability of flaxseed on blood pressure (BP) lowering was invetiaged in this systematic meta-analysis of data from 15 eligible trials with 19 treatment arms. The results showed significant reductions in both systolic (SBP) and diastolic (DBP) after supplementation with flaxseed products. There was a greater effect on SBP in subset of trials with >12 weeks of duration versus a subset lasting <12 weeks. With respect to DBP, there was a similar effect of treatment duration. Reduction of SBP was significant with milled flaxseed but not oil and lignan extract. DBP was significantly reduced with milled seed and oil but not lignan extract. The authors speculate that the hypotensive effects of flaxseed may be caused by synergistic action of potent antioxidants as lignans and/or by different bioactive ingredients such as SDG and ALA.
ABSTRACT:
Background & aims: Many experimental and clinical trials suggested that flaxseed might be a potent antihypertensive, but the evidences concerning the effects of flaxseed supplements on blood pressure (BP) has not been fully conclusive. We aimed to assess the impact of the effects of flaxseed supplements on blood pressure through systematic review of literature and meta-analysis of available randomized controlled trials (RCTs). Methods: The literature search included PUBMED, Cochrane Library, Scopus, and EMBASE up to February2015 to identify RCTs investigating the effect of flaxseed supplements on plasma blood pressure. Effect size was expressed as weighed mean difference (WMD) and 95% confidence interval (CI).
Results: 15 trials (comprising 19 treatment arms) with 1302 participants were included in this meta-analysis. Random-effects meta-analysis suggested significant reductions in both systolic BP (SBP) (WMD: -2.85 mmHg, 95%CI: -5.37 to -0.33, p = 0.027) and diastolic BP (DBP) (WMD: -2.39 mmHg, 95%CI: -3.78 to -0.99, p = 0.001) following supplementation with flaxseed products. When the studies were stratified according to their duration, there was a greater effect on both SBP and DBP in the subset of trials with -12 weeks of duration (WMD: -3.10 mmHg, 95%CI: -6.46 to 0.27, p = 0.072 and -2.62 mmHg, 95%CI: -4.39 to -0.86, p = 0.003, respectively) vs the subset lasting <12 weeks (WMD: -1.60 mmHg, 95%CI: -5.44 to 2.24, p = 0.413, and -1.74 mmHg, 95%CI: -4.41 to 0.93, p = 0.202, respectively). Another subgroup analysis was performed to assess the impact of flaxseed supplement type on BP. Reduction of SBP was significant with flaxseed powder (WMD: -1.81 mmHg, 95% CI: -2.03 to -1.59, p < 0.001) but not oil (WMD: -4.62 mmHg, 95%CI: -11.86 to 2.62, p = 0.211) and lignan extract (WMD: 0.28 mmHg, 95% CI: -3.49 to 4.04, p = 0.885). However, DBP was significantly reduced with powder and oil preparations (WMD: -1.28 mmHg, 95% CI: -2.44 to -0.11, p = 0.031, and -4.10 mmHg, 95%CI: -6.81 to -1.39, p = 0.003, respectively), but not with lignan extract (WMD: -1.78 mmHg, 95% CI: -4.28 to 0.72, p = 0.162). Conclusions: This meta-analysis of RCTs showed significant reductions in both SBP and DBP following supplementation with various flaxseed products. (Authors abstract)
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