The healthy Nordic dietary pattern has no effect on inflammatory markers: A systematic review and meta-analysis of randomized controlled clinical trials

Objectives: The Nordic diet (ND) is regarded as a healthy dietary pattern that might beneficially affect systemic chronic inflammation; however, the results of published studies are conflicting. The present systematic review and meta-analysis aimed to summarize the published evidence by randomized controlled clinical trials with regard to the effect of the ND pattern on circulating inflammatory markers such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha). Methods: PubMed, ISI Web of Science, Scopus, and Google Scholar were searched up to October 2017 to identify relevant studies. The risk of bias in the included studies was assessed using Cochrane's collaboration tool. The overall effects were calculated using the random effects model. Results: Seven studies were eligible to be included in the systematic review. All studies were conducted in Nordic countries. The meta-analysis of six eligible clinical trials included 613 adult participants and showed that adherence to the ND does not significantly affect circulating CRP levels (weighted mean difference [WMD]: -0.17 mg/L; 95% confidence interval [CI], -0.69 to 0.35; P=0.529). The meta-analysis of three studies that reported on the effect on other inflammatory makers also failed to find any significant effect on TNF-alpha (WMD: 0.23 mg/L; 95% CI, -0.75 to 1.21; P=0.645) and IL-6 (WMD: 0.13 mg/L, 95% CI, -0.29 to 0.56; P=0.539) concentrations. Conclusions: Adherence to the ND pattern does not seem to affect circulating CRP, IL-6, and TNF-alpha levels. Clinical trials with longer follow-up periods and including participants in other regions are highly recommended. (C) 2018 Elsevier Inc. All rights reserved.