The effect of beetroot juice (BRJ) supplementation on exercise-induced muscle damage (EIMD): a systematic review and dose-response meta-analysis of randomized controlled trials.

OBJECTIVE: This systematic review and meta-analysis was conducted to quantify the effect of beetroot juice (BRJ) supplementation on exercise-induced muscle damage (EIMD), inflammatory biomarkers, muscle function, and muscle soreness. METHODS: The Robvis tool was used for assessing the risk of bias. The mean differences (MD) and 95% confidence intervals (CI) of creatine kinase (CK) levels (IU/L), C-reactive protein (CRP), interleukin (IL)-6, and tumor necrosis factor-alpha (TNF-α) (pg/ml), maximal voluntary isometric contraction (MVIC), counter movement jump (CMJ), and pressure pain threshold (PPT) (% change from baseline) were pooled using either a fixed- or random-effects model. Between-study heterogeneity was assessed using the χ2 or I 2 statistic. RESULTS: Seven trials met the eligibility criteria and were included in the pooled analysis. Meta-analysis indicated that BRJ supplementation significantly reduced serum CK levels [weighted mean difference (WMD) = -98.67 IU/L, 95% CI (-122.14 to -75.21), I 2 = 74.2%]. Significant improvement was also observed in MVIC [WMD = 8.93%, 95% CI (7.59-10.28), I 2 = 81.2%], CMJ [WMD = 4.72%, 95% CI (4.14-5.30), I 2 = 46.3%], and PPT [WMD = 7.22%, 95% CI (5.30-10.93), I 2 = 49.4%] from baseline in the intervention group compared to the placebo group. However, no significant change in CRP, IL-6, and TNF-α levels was found. Dose-response analysis revealed that there is a significant non-linear association between the daily dose and antioxidant content (Trolox) of BRJ and the final effect size regarding CK. CONCLUSION: BRJ supplementation may improve some aspects of EIMD, including muscle damage, muscle function, and recovery.