Effect of flaxseed supplementation on markers of inflammation and endothelial function: A systematic review and meta-analysis

Objectives: The rationale for the current study was to evaluate the efficacy of flaxseed supplementation on important adhesion molecules and inflammatory cytokines in adults. Methods: We conducted searches of published literature in PubMed, Scopus, Web of Science, and Google Scholar databases from inception until May 2019. All randomized controlled trials (RCTs) which investigated the effects of flaxseed supplementation on the circulating concentrations of C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), vascular cell adhesion protein 1 (VCAM-1), E-selectin, and intercellular adhesion molecule 1 (ICAM-1) were included in our analysis. Results were summarized using weighted mean differences (WMDs) by random-effects model. Results: Forty eligible RCTs, including 2520 participants were identified. The results of the meta-analysis revealed flaxseed supplementation reduced the concentrations of CRP (WMD = - 0.387 mg/L; 95% CI: - 0.653, - 0.121, p = 0.004), IL-6 (WMD = - 0.154 pg/Ml; 95% CI: - 0.299, - 0.010, p = 0.036), and VCAM-1 (WMD = -22.809 ng/ml; 95% CI: - 41.498, - 4.120, p = 0.017) but had no significant effect on TNF-alpha (WMD = -0.077 pg/mL; 95% CI: - 0.317, 0.163, p = 0.530), ICAM-1 (WMD = - 8.610 ng/ml; 95% CI: - 21.936, 4.716, p = 0.205), and E-selectin (WMD = - 1.427 ng/ml; 95% CI: - 4.074, 1.22, p = 0.291). Conclusions: These findings showed that flaxseed supplementation may improve some circulating concentrations of specific adhesion molecules and inflammatory cytokines. However, well-designed trials are needed to confirm the range of non-significant and/or equivocal findings.