TABLE 1.
Trial characteristics1
| Trials included in the primary analysis (n = 29) | Population | Size | Age | Male | BP medication | Trial design | Trial length2 | Intervention (per day) | Control | Baseline SBP | Baseline DBP | Baseline ascorbic acid3 | BP measurement: position, location, device, no. of measurements |
| n | y | % | wk | mm Hg | mm Hg | μmol/L | |||||||
| Farvid, 2010 (18)4 | T2D | 75 | 52.5 ± 8.55 | 52 | No | P, D | 16 | Vit C 400 mg, vit E 200 mg, Mg 500 mg, zinc 40 mg, thiamine 20 mg, riboflavin 20 mg, vit B-6 20 mg, vit B-12 20 μg, folic acid 2 mg | Placebo | 130.3 ± 15.59 | 82.8 ± 10.00 | 48.8 ± 14.8 | Seated, arm, Powerlab sphygmomanometer, 2 |
| Shargorodsky, 2010 (27)4 | Patients with cardiovascular risk factors | 70 | 62.6 ± 5.7 | 51 | Yes | P, S | 24 | Vit C 1000 mg, vit E 400 IU, coenzyme Q10 120 mg, selenium 200 μg | Placebo | 141.7 ± 23.3 | 77.2 ± 10.0 | — | Supine, NA, NA, NA |
| Wang, 2009 (33)4 | Obese women | 64 | 42.0 ± 6.9 | 0 | Yes | P, D | 26 | Vit C 60 mg, multiple vitamins and minerals | Maize starch | 128.0 ± 22.9 | 85.0 ± 14.2 | — | NA, arm, standard mercury sphygmomanometer, 2 |
| Farah, 2008 (11)4 | Essential hypertension | 16 | 26–576 | 56 | Yes | P, O | 24 | Vit C 500 mg, vit E 600 IU, lercanidipine 10 mg | Lercanidipine 10 mg | 159.6 | 96.2 | — | — |
| Rodrigo, 2008 (12)4 | Essential hypertension | 110 | 45.6 ± 11.5 | 100 | No | P, D | 8 | Vit C 1000 mg, vit E 400 IU | Placebo | 138.7 ± 5.9 | 97.0 ± 6.3 | 37.5 ± 18.9 | NA, arm, oscillometric monitor (Spacelabs 90207), NA |
| Mahajan, 2007 (13)4 | Essential hypertension | 40 | 37.3 ± 7.7 | 100 | Yes | P, O | 12 | Vit C 1000 mg, amlodipine 5 mg | Amlodipine 5 mg | 159.1 ± 8.6 | 96.1 ± 3.9 | — | NA, NA, NA, 1 |
| Nightingale, 2007 (15) | CHF and left ventricular systolic dysfunction | 37 | 63.5 ± 8.6 | 84 | Yes | P, D | 4 | Vit C 4000 mg | Placebo | 130 ± 34 | 75 ± 15 | 39.05 ± 28.19 | NA, thigh and ankle, peripheral pulse waveform recorder (QYLP84), NA |
| Plantinga, 2007 (16) | Essential hypertension | 30 | 50 (42–60)7 | 100 | No | X, D | 8 | Vit C 1000 mg, vit E 400 IU | Placebo | 135 ± 10 | 87 ± 7 | 39.12 ± 22.43 | Supine, arm, automatic device (OMRON-950), 3 |
| Farvid, 2005 (17) | T2D | 76 | 51 ± 9 | 46 | No | F, P, D | 12 | Vit C 200 mg, vit E 100 IU, zinc 15 mg, Mg 100 mg | Placebo, zinc 15 mg, Mg 100 mg | 126 ± 16 | 84 ± 10 | 62.28 ± 18.58 | Seated, NA, NA, 2 |
| Hutchins, 2005 (19) | Healthy postmenopausal women | 10 | 56 ± 8 | 0 | No | F, X, D | 2 | Vit C 500 mg, soy isoflavones 5 mg (per kg/body weight) | Placebo, soy isoflavones 5 mg | — | — | 49.4 ± 11.4 | Seated, arm, sphymomanometer (Sprague Rappaport), 1 |
| Ward, 2005 (20)4 | Hypertension | 38 | 62 ± 7 | 70 | Yes | F, P, D | 6 | Vit C 500 mg | Placebo | 133.8 ± 9.1 | 79.5 ± 7.5 | 40.5 ± 13.5 | Ambulatory, arm, oscillometric ABPM monitor (Spacelabs 90207), 648 |
| Magen, 2004 (21) | Hyperlipidemic subjects with resistant hypertension | 369 | 52.0 ± 12.5 | 52 | Yes | P, S | 8 | Vit C 500 mg | Placebo | 150.8 ± 6.4 | 86.4 ± 4.7 | — | Ambulatory, arm, ABPM monitor (Profilomat), 66 |
| Schutte, 2004 (22)4 | Healthy normotensive white men | 38 | 22.0 ± 2.1 | 100 | No | P, D | 12 | Vit C 1000 mg, vit E 800 mg, folate 10 mg | Placebo | 128.9 ± 9.0 | 79.1 ± 6.2 | — | Fowler's position, finger, Finometer, NA |
| Nightingale, 2003 (14) | CHF and left ventricular systolic dysfunction | 45 | 59.0 ± 8.7 | 74 | Yes | P, D | 4 | Vit C 2000 mg | Placebo | 126 ± 24 | 73 ± 11 | 44.4 ± 18.2 | NA, arm, Finapres (Ohmeda)/Portapres (TNO), NA |
| Block, 2002 (23)4 | Smokers | 1119 | 43.7 ± 13.4 | 38 | No | P, D | 8 | Vit C 515 mg | Placebo | 117.0 ± 11.8 | 75.9 ± 9.5 | 51.7 | Seated, arm, mercury sphygmomanometer, 2 |
| Brody, 2002 (28) | Healthy young recruits | 120 | 25.0 ± 4.2 | 39 | No | P, D | 2 | Sustained-release vit C 3000 mg | Placebo | — | — | 82.6 | NA, arm, self-inflating sphygmomanometer, 1 |
| Darko, 2002 (24) | Uncomplicated T2D | 35 | 56.0 ± 6.5 | 66 | Yes | P, D | 3 | Vit C 1500 mg | Placebo | 140 ± 19 | 78 ± 11 | 55 ± 23 | Supine, arm, automated measuring device (Dynamap), 3 |
| Mullan, 2002 (25)4 | T2D | 30 | 59.5 ± 6.6 | 73 | Yes | P, D | 4 | Vit C 500 mg | Placebo | 141.6 ± 12.6 | 83.9 ± 5.1 | 43.3 ± 19.3 | Supine, arm, oscillometric sphygmomanometer (OMRON HEM 705CP), 3 |
| Singh, 2002 (26) | Healthy older subjects | 36 | 67 ± 7 | 50 | No | P, D | 6 | Vit C 1000 mg | Placebo | 135 ± 19 | 79 ± 11 | 83 ± 19 | Seated, arm, oscillometric sphygmomanometer (OMRON HEM 705CP), 3 |
| Duffy, 2001 (29)4 | Healthy patients with hypertension | 45 | 33.9 ± 12.1 | 49 | Yes | P, D | 4 | Vit C 500 mg | Placebo | 156 ± 21 | 88 ± 12 | 48.9 ± 17.7 | Semirecumbent, arm, automated monitor (Dinamap), 3 |
| Gaede, 2001 (30) | T2D | 30 | 58.7 ± 7.3 | 69 | Yes | X, D | 4 | Vit C 1250 mg, vit E 680 IU | Placebo | 155 ± 18 | 91 ± 10 | 41.9 ± 18.4 | Supine, arm, Hawksley Random Zero Sphygmomanometer, 4 |
| Fotherby, 2000 (31)4 | Normotensive and hypertensive older adults | 40 | 72 ± 4 | 50 | No | X, D | 12 | Vit C 500 mg | Placebo | 135 ± 15 | 79 ± 9 | 49 ± 14 | Ambulatory, arm, oscillometric ABPM monitor (Spacelabs 90207), 60 |
| Title, 2000 (32) | Coronary artery disease | 50 | 58.0 ± 10.7 | 76 | Yes | P, D | 16 | Vit C 2000 mg, vit E 800 IU, folic acid 5 mg | Folic acid 5 mg | 133 ± 18 | 81 ± 11 | — | — |
| Gokce, 1999 (35) | Coronary artery disease | 55 | 55 ± 10 | 91 | Yes | P, D | 4 | Vit C 500 mg | Placebo | 138 ± 22 | 77 ± 9 | 42 ± 17 | — |
| Galley, 1997 (36)4 | Normotensive and hypertensive outpatients | 40 | 25–73 | — | Yes | X, D | 8 | Vit C 500 mg, α-tocopherol 600 mg, β-carotene 30 mg, zinc sulfate 200 mg | Placebo | 107–207 | 67.0–110.010 | — | Supine, arm, mercury sphygmomanometer, 3 |
| Ghosh, 1994 (37)4 | Elderly patients with hypertension | 48 | 73.8 ± 5.1 | 38 | No | P, D | 6 | Vit C 500 mg | Placebo | 175.3 ± 16.0 | 90.7 ± 11.6 | 51.7 ± 17.5 | Seated, arm, Hawksley Random Zero Sphygmomanometer, 3 |
| Salonen, 1994 (38)4 | Normotensive male smokers | 40 | 30–58 | 100 | No | P, D | 12 | Vit C 400 mg, selenium 100 μg, d-α-tocopheryl acetate 200 mg, β-carotene 30 mg | Placebo | 140.9 ± 15.5 | 84.5 ± 9.9 | 49.0 ± 20.7 | Seated, arm, mercury sphygmomanometer, 2 |
| Osilesi, 1991 (39)4 | Hypertensive and normotensive outpatients | 20 | 57.8 ± 14.3 | 25 | No | X, D | 6 | Vit C 1000 mg | Placebo | 139 ± 18 | 81 ± 12 | 7411 | Supine and seated, arm, mercury sphygmomanometer, 4 |
| Keith, 1982 (34) | Smoking and nonsmoking men | 22 | 29.2 ± 4.2 | 100 | No | X, D | 3 | Vit C 300 mg | Citric acid | 125 ± 10 | 73 ± 7 | 44.08 ± 15.02 | Supine, arm, 112 |
1
ABPM, ambulatory blood pressure monitoring; BP, blood pressure; CHF, congestive heart failure; D, double-blind; DBP, diastolic blood pressure; F, factorial trial; NA, not available; O, no blinding; P, parallel trial; S, single blind; SBP, systolic blood pressure; T2D, type 2 diabetes; Vit/vit, vitamin; X, crossover trial.
2
Months were converted to weeks by using 1 mo = 4 wk; years were converted by using 1 y = 52 wk.
3
Values were multiplied by 56.78 to convert mg/dL to μmol/L.
4
Trial reported a significant end-baseline reduction in SBP or DBP.
5
Mean ± SD (all such values).
6
Range (all such values).
7
Mean; range in parentheses.
8
Estimated assuming an 8-h night, 16-h day.
9
Size approximated because of unknown randomization of dropouts.
10
Range of normotensive subjects only.
11
Based on end-placebo values.
12
Obtained from a previously published trial design article (52).