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Table 5 Polyphenol meta-analysis and sub-group analyses

From: Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials

  All polyphenol trials Trials with polyphenols quantified
  k n SMD (95% CIs) p I2 (%) k n SMD (95% CIs) p I2 (%)
Overall 71 1227 0.17 [0.10, 0.25] <0.001 66 45 829 0.20 [0.09, 0.30] <0.001 72
Design    Qb: 0.04 0.548     Qb: 3.53 0.060  
Crossover 52 730 0.16 [0.08, 0.23] <0.001 65 34 481 0.14 [0.04, 0.24] 0.006 66
Parallel 19 497 0.24 [-0.02, 0.49] 0.069 56 12 348 0.47 [0.14, 0.81] 0.006 59
Blinding    Qb: 0.34 0.845     Qb: 0.13 0.714  
Single blind 6 122 0.30 [-0.3, 0.91] 0.329 91 6 122 0.30 [-0.30, 0.91] 0.329 91
Double blind 58 987 0.17 [0.10, 0.24] <0.001 51 38 674 0.19 [0.08, 0.29] <0.001 67
Unclear 7 118 0.10 [-0.27, 0.46] 0.621 76 1 33 -0.18 [-0.8, 0.44] 0.572 -
Supplementation duration    Qb: 0.12 0.733     Qb: 1.46 0.228  
Acute 15 243 0.21 [0.003, 0.41] 0.046 85 5 101 0.56 [-0.07, 1.19] 0.081 95
Multiple days 56 984 0.17 [0.09, 0.25] <0.001 57 40 728 0.17 [0.07, 0.27] 0.001 61
Polyphenol quantification    Qb: 1.13 0.287       
No 26 398 0.14 [0.04, 0.25] 0.009 52      
Yes 45 829 0.2 [0.09, 0.30] <0.001 72      
Sex1    Qb: 7.49 0.024     Qb: 0.31 0.210  
Male 45 729 0.23 [0.15, 0.32] <0.001 42 31 556 0.20 [0.08, 0.32] <0.001 46
Female 4 71 0.01 [-0.19, 0.20] 0.948 0 3 55 0.01 [-0.19, 0.21] 0.942 0
Mixed 19 388 0.05 [-0.09, 0.19] 0.460 78 8 179 0.26 [-0.05, 0.57] 0.098 94
Performance level    Qb: 12.90 0.005     Qb: 1.17 0.558  
PL1 3 89 0.76 [0.37, 1.15] <0.001 0 2 80 0.59 [-0.08, 1.25] 0.083 0
PL1 Females -      -     
PL1 Males: 3 89 0.76 [0.37, 1.15] <0.001 0 2 80 0.59 [-0.08, 1.25] 0.083 0
GXT 2 80 0.59 [-0.08, 1.25] 0.083 0 2 80 0.59 [-0.08, 1.25] 0.083 0
TT 1 9 0.86 [0.38, 1.34] <0.001 - -     
PL2 19 279 0.12 [0, 0.25] 0.059 36 14 207 0.21 [0.09, 0.34] <0.001 0
PL2 Females -      -     
PL2 Males: 17 239 0.21 [0.11, 0.32] <0.001 0 14 207 0.21 [0.09, 0.34] <0.001 0
GXT 6 94 0.23 [-0.02, 0.47] 0.068 16 6 94 0.23 [-0.02, 0.47] 0.068 16
IGXT 1 26 2.54 [0.13, 4.96] 0.039 - 1 26 2.54 [0.13, 4.96] 0.039 -
ITTE 1 13 0.26 [-0.18, 0.7] 0.252 - 1 13 0.26 [-0.18, 0.7] 0.252 -
TT 6 64 0.18 [0.01, 0.35] 0.042 0 5 54 0.21 [0.02, 0.39] 0.028 0
TTE 3 42 0.21 [0.03, 0.4] 0.021 0 1 20 0.12 [-0.21, 0.45] 0.492 -
PL3 18 275 0.22 [0.08, 0.36] 0.002 31 13 219 0.22 [0.06, 0.34] 0.002 36
PL3 Females 2 44 0.05 [-0.17, 0.28] 0.646 0 2 44 0.05 [-0.17, 0.28] 0.646 0
PL3 Males: 16 231 0.28 [0.14, 0.42] <0.001 36 11 175 0.28 [0.08, 0.49] 0.006 39
IGXT 1 13 0.54 [0.1, 0.97] 0.016 - 1 13 0.54 [0.1, 0.97] 0.016 -
TT 11 177 0.24 [0.08, 0.41] 0.004 59 9 152 0.24 [0.03, 0.46] 0.029 42
TTE 4 57 0.35 [-0.01, 0.71] 0.056 20 1 10 1.1 [-1.02, 3.22] 0.314 -
PL4 2 19 0.49 [0.21, 0.77] <0.001 0 1 9 0.41 [0.08, 0.75] 0.015 -
PL4 Females -      -     
PL4 Males: 2 19 0.49 [0.21, 0.77] <0.001 0 1 9 0.41 [0.08, 0.75] 0.015 -
TT 2 19 0.49 [0.21, 0.77] <0.001 0 1 9 0.41 [0.08, 0.75] 0.015 -
PL5 -      -     
Exercise mode    Qb: 6.32 0.097     Qb: 10.15 0.006  
Cycling 39 589 0.15 [0.06, 0.24] 0.001 54 27 431 0.14 [0.04, 0.23] 0.004 40
Incline Walk/Run 4 83 0.54 [0.21, 0.87] 0.001 0 2 60 0.63 [0.02, 1.24] 0.043 0
Rowing 2 37 -0.32 [-1.34, 0.71] 0.556 63 1 19 -0.84 [-1.74, 0.05] 0.064 -
Running 24 489 0.22 [0.10, 0.33] <0.001 62 13 290 0.44 [0.17, 0.71] 0.001 82
Swimming 1 11 -0.18 [-0.63, 0.27] 0.434 - 1 11 -0.18 [-0.18, 0.27] 0.112 -
Climbing 1 18 -0.62 [-1.0, -0.25] 0.001 - 1 18 -0.62 [-1.0, -0.25] 0.001 -
Test type    Qb: 10.29 0.016     Qb: 11.46 0.009  
GXT 17 352 0.14 [-0.001, 0.28] 0.052 23 11 249 0.22 [0.04, 0.39] 0.016 37
IGXT 4 73 1.09 [0.50, 1.68] <0.001 66 4 73 1.09 [0.50, 1.68] <0.001 66
ITTE 1 13 0.26 [-0.18, 0.70] 0.252 - 1 13 0.26 [-0.18, 0.70] 0.252 -
TT 35 549 0.12 [0.03, 0.21] 0.011 59 24 370 0.10 [0.01, 0.20] 0.037 41
TTE 14 240 0.16 [0.01, 0.31] 0.037 63 5 124 0.17 [-0.39, 0.72] 0.563 88
Test duration    Qb: 2.40 0.663     Qb: 5.57 0.135  
<5 mins: 4 49 0.26 [-0.08, 0.59] 0.133 91 1 12 -0.08 [-0.21, 0.06] 0.257 -
TT 2 21 0.36 [-0.55, 1.27] 0.446 93 1 12 -0.08 [-0.21, 0.06] 0.257 -
TTE 2 28 0.20 [0.07, 0.33] 0.002 0 -     
5-10 mins: 9 124 0.08 [-0.14, 0.30] 0.472 73 4 56 -0.11 [-0.43, 0.22] 0.532 76
TT 3 36 -0.01 [-0.16, 0.14] 0.873 0 2 18 -0.02 [-0.17, 0.13] 0.807 0
TTE 6 88 0.11 [-0.23, 0.45] 0.532 80 2 38 -0.25 [-0.97, 0.48] 0.516 88
10-30 mins: 19 339 0.19 [0.12, 0.26] <0.001 0 12 234 0.22 [0.1, 0.33] <0.001 14
TT 16 264 0.21 [0.1, 0.32] <0.001 27 10 176 0.21 [0.06, 0.36] 0.006 35
TTE 3 75 0.18 [0.02, 0.34] 0.031 0 2 58 0.21 [0.03, 0.4] 0.024 0
30-60 mins: 9 122 0.12 [0.03, 0.21] 0.008 0 6 77 0.11 [0.01, 0.2] 0.036 0
TT 7 101 0.12 [0.03, 0.21] 0.008 0 6 77 0.11 [0.01, 0.2] 0.036 0
TTE 2 21 0.04 [-0.32, 0.41] 0.828 19 -     
>60 mins: 5 104 0.14 [-0.38, 0.66] 0.608 83 3 64 0.52 [-0.2, 1.4] 0.206 71
TT 4 76 -0.08 [-0.46, 0.29] 0.673 65 2 36 0.33 [-0.61, 1.27] 0.506 75
TTE 1 28 0.97 [0.21, 1.73] 0.013 - 1 28 0.97 [0.21, 1.73] 0.013 -
Overall (TT & TTE) 46 738 0.14 [0.06, 0.21] <0.001 59 26 443 0.11 [0.01, 0.21] 0.038 61
  1. 1 Sex not specified in three trials. Abbreviations – GXT, graded exercise test; IGXT, intermittent graded exercise test; ITTE, intermittent time to exhaustion; k, number of trials; LCI, lower confidence interval; n, pooled sample size; PL, performance level; Qb, between-group Q-statistic; SMD, standardised mean difference (Hedge’s g); TT, time-trial; TTE, time to exhaustion; UCI, upper confidence interval