Thirteen trials of 14 separate study populations were included (n=284). There were 5 double-blind randomised controlled trials (RCTs; n=95), 2 single-blind RCTs (n=25), 3 double-blind crossover trials (n=97), 1 single-blind crossover trial (n=20) and 2 baseline comparison studies (n=47).
The weighted mean baseline and post-treatment systolic BPs were 149.6 (± 11.1) mmHg and 145.7 (± 11.0) mmHg, respectively, representing a decrease of 3.9 mmHg. Seven of the 14 study populations showed a significant difference between baseline and post-treatment systolic BP (p-value ranged from p<0.001 to p<0.05).
The weighted mean baseline and post-treatment diastolic BPs were 84.6 (± 4.4) mmHg and 82.5 (± 4.1) mmHg, respectively, representing a decrease of 2.1 mmHg. Only 2 studies found a significant reduction in diastolic BP between baseline and post-treatment (p=0.003, p=0.03).
Plasma vitamin C levels significantly increased in all 7 studies that measured it. The average change across all trials was 40.7 μmol.
A subgroup analysis comparing the 4 diabetic populations with the other 10 group populations found no significant differences between these groups on any of the outcome measures.