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Table 3 Subgroup analysis to assess the effect of grape polyphenols supplementation on different biomarkers of oxidative stress levelsa

From: The effect of grape products containing polyphenols on oxidative stress: a systematic review and meta-analysis of randomized clinical trials

Serum enzyme Number of trials WMD 95% CI (upper limit, lower limit) P value
SOD
 Health status
  Unhealthy 4 < 0.001 (−0.001, 0.001) 0.99
  Healthy 4 0.450 (0.23, 0.66)b < 0.001
Duration of study
 10 wk. or more 4 0.085 (−0.01, 0.18)b 0.09
 lower than 10 wk 4 0.001 (−0.006, 0.007) 0.86
Dose of grape polyphenols
 400 mg/d or more 4 0.539 (0.24, 0.82)b < 0.001
 Lower than 400 mg/d 4 < 0.001 (−0.001, 0.001) 0.75
Type of study
 Cross-over 4 0.539 (0.24, 0.82)b < 0.001
 Parallel 4 < 0.001 (−0.001, 0.001) 0.75
Study quality
 Good 4 0.085 (−0.01, 0.18) 0.08
 Fair 3 < -0.001 (−0.001, 0.001) 0.75
 Weak 1 2.399 (2.01, 2.78)b <  0.001
TAC
 Health status
  Unhealthy 2 −0.254 (−0.65, 0.14) 0.21
  Healthy 4 2.829 (0.13, 5.52)b 0.04
Duration of study
 More than 6 wk 3 3.814 (−4.14, 11.77) 0.34
 6 wk. or lower 3 0.084 (−0.36, 0.52) 0.71
Dose of grape polyphenols
 More than 650 mg/d 2 −0.058 (−0.22, 0.11) 0.49
 650 mg/d or lower 4 2.595 (−2.53, 7.72) 0.32
Type of study
 Cross-over 3 2.785 (0.01, 5.55)b 0.04
 Parallel 3 −0.164 (−0.65, 0.33) 0.51
Study quality
 Good 3 −0.145 (−1.18, −0.10)c <  0.001
 Fair 2 0.266 (−0.22, 0.75) 0.28
 Weak 1 8.01 (7.54, 8.49)b <  0.001
ORAC
Health status
 Abnormal wt.d 2 −0.030 (−0.46, 0.40) 0.89
 Healthy 3 0.524 (0.42, 0.62)b <  0.001
Duration of study
 10 wk. or more 2 0.543 (0.43, 0.64)b <  0.001
 Lower than 10 wk 3 0.089 (−0.26, 0.44) 0.62
Dose of grape polyphenols
More than 400 mg/d  2 0.377 (0.08, 0.67)b 0.01
 400 mg/d or lower 3 0.161 (−0.26, 0.58) 0.46
Type of study
 Cross-over 4 0.210 (−0.15, 0.57) 0.25
 Parallel 1 −140.0 (−651.9, 371.9) 0.59
Study quality
 Good 2 0.365 (0.01, 0.71)b 0.03
 Fair 2 − 0.251 (−0.36, −0.13)c <  0.001
 Weak 1 0.377 (0.08, 0.67)b 0.01
MDA
  Health status
Unhealthy  3 − 0.092 (−0.50, 0.32) 0.66
Healthy   4 −0.214 (−0.62, 0.19) 0.30
Duration of study
8 wk. or more  5 −0.149 (−0.47, 0.17) 0.36
Lower than 8 wk.  2 0.096 (−1.14, 1.33) 0.88
Dose of grape polyphenols
600 mg/d or more  4 −0.237 (−0.58, 0.11) 0.18
Lower than 600 mg/d  3 −0.034 (−0.88, 0.81) 0.93
Type of study
Cross-over  2 0.003 (−0.05, 0.05) 0.90
Parallel  5 −0.328 (−0.79, 0.14) 0.17
Study quality
 Good 4 −0.072 (−0.55, 0.40) 0.77
 Fair 3 −0.313 (−0.67, 0.05) 0.09
GPX
 Health status
  Unhealthy 2 0.009 (−0.02, 0.04) 0.60
  Healthy 3 0.044 (−0.03, 0.12) 0.30
Duration of study
 More than 10 wk 3 −0.002 (−0.01, 0.01) 0.83
 10 wk. or lower 2 0.068 (−0.07, 0.20) 0.33
Dose of grape polyphenols
 400 mg/d or more 3 0.063 (−0.02, 0.15) 0.16
 Lower than 400 mg/d 2 < 0.001 (−0.001, 0.001) 0.80
Type of study
 Cross-over 3 0.063 (−0.02, 0.15) 0.16
 Parallel 2 < 0.001 (−0.001, 0.001) 0.80
Study quality
 Good 3 0.063 (−0.02, 0.15) 0.16
 Fair 2 < 0.001 (−0.001, 0.001) 0.80
  1. a CI confidence interval, GPX Glutathione Peroxidase, MDA malondialdehyde, ORAC Oxygen Radical Absorbance Capacity, SE standard error, SOD Superoxide Dismutase, TAC Total Antioxidant Capacity, WMD weighted mean difference, wt weight
  2. b Significant increase in the outcome was observed
  3. c Significant decrease in the outcome was observed
  4. d Abnormal weight that is, participants were obese or overweight