Effect of Flaxseed Intervention on Inflammatory Marker C-Reactive Protein: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Functional food-flaxseed and its derivatives (flaxseed oil or lignans) are beneficial for human health, possibly because of their anti-inflammatory effects. C-reactive protein (CRP), a sensitive marker of inflammation was chosen to evaluate the anti-inflammatory effects of flaxseed. We searched randomized controlled trials from PubMed and the Cochrane Library in October 2015 and conducted a meta-analysis to evaluate the effectiveness of flaxseed and its derivatives on CRP. The mean differences (net change) in CRP (mg/L) concentrations were pooled with a random- or a fixed-effects model depending on the results of heterogeneity tests. Overall, flaxseed interventions had no effects on reduction of CRP (p = 0.428). The null effects were consistent in the subgroup analysis with multiple studies and population characteristics. Significant heterogeneity was observed in most of the analyses. Meta-regression identified baseline body mass index (BMI) as a significant source of heterogeneity (P-interaction = 0.032), with a significant reduction in CRP of 0.83 mg/L (95% confidence interval -1.34 to -0.31; p = 0.002) among subjects with a BMI of ≥30 kg/m². In conclusion, our meta-analysis did not find sufficient evidence that flaxseed and its derivatives have a beneficial effect on reducing circulating CRP. However, they may significantly reduce CRP in obese populations.