The Effects of Conjugated Linoleic Acid Supplements on Biomarkers of Oxidative Stress in Human Studies: A Systematic Review and Meta-Analysis

Background: Oxidative stress is the leading cause of chronic disorders. The aim of the present study is to assess the effects of conjugated linoleic acid (CLA) supplements on oxidative stress biomarkers in adults. Methods: PubMed, Web of Science, Google Scholar, ProQuest, Scopus, and Embase were searched up to December 2020. All clinical trials that evaluated the effect of CLA on malondialdehyde (MDA), GSH-peroxidase (GPX), and 8-IsoprostanesF2α (8-iso-PGF2α) were included. Results: Twelve eligible studies were included in the meta-analysis. A significant increase was observed in 8-iso-PGF2α level (SMD=1.48 nmol/mmol of creatinine; 95% CI: 1.11 to 1.85) with low heterogeneity level (I2= 31.5%, and P=0.199). This effect was also significant in both subgroups of healthy and metabolic disorder individuals. Moreover, after Hartung-Knapp adjustment, the results remained significant. No significant changes were found in MDA (SMD=-0.34 µmol/l; 95% CI: -0.82 to 0.14) and GPX (SMD=0.31 U/gHb; 95% CI: -0.03 to 0.66) levels. However, after Hartung-Knapp adjustment, the results became significant for GPX level (SMD=0.31, 95% CI: 0.04 to 0.59). Conclusion: CLA supplementation could significantly increase some markers of oxidative stress such as 8-iso-PGF2α level and GPX level, without any significant effect on MDA level.