TABLE 2.

Subgroup analyses of mean change in BP¹

	Change in SBP				Change in DBP
Subgroup	No. of trials	Effect	95% CI	P	No. of trials	Effect	95% CI	P
		mm Hg	mm Hg			mm Hg	mm Hg
Hypertension
Yes	13	−4.85	−7.50, −2.20	0.28	12	−1.67	−4.05, 0.72	0.85
No	18	−3.11	−4.52, −1.71		17	−1.37	−3.10, 0.35
Diabetes
Yes	5	−4.71	−8.73, −0.68	0.63	5	−4.06	−6.72, −1.40	0.08
No	26	−3.70	−5.28, −2.11		24	−0.94	−2.45, 0.57
Baseline ascorbic acid
<49.0 μmol/L	11	−4.95	−7.96, −1.93	0.28	11	−2.43	−5.30, 0.44	0.53
≥49.0 μmol/L	11	−3.09	−4.66, −1.52		11	−1.61	−2.82, −0.40
Mean age
<50 y	12	−5.07	−7.22, −2.92	0.04	11	−2.44	−4.87, −0.01	0.19
50–60 y	13	−3.59	−6.23, −0.94		12	−1.43	−3.99, 1.13
>60 y	6	−1.85	−2.94, −0.77		6	0.03	−1.49, 1.55
Duration
<8 wk	15	−2.89	−4.43, −1.36	0.43	15	−0.60	−2.15, 0.94	0.37
≥8 wk	16	−4.45	−6.63, −2.27		14	−2.34	−4.55, −0.14
Vitamin C dose
<500 mg/d	6	−4.79	−7.25, −2.33	0.26	6	−2.96	−6.76, 0.85	0.72
500 mg/d	11	−2.89	−4.50, −1.29		9	−0.27	−2.24, 1.71
>500 mg/d	14	−2.96	−5.58, −0.34		14	−1.50	−3.56, 0.56
Study design
Crossover	9	−2.96	−4.34, −1.57	0.51	7	−0.10	−1.59, 1.39	0.17
Parallel	22	−4.17	−6.27, −2.07		22	−2.07	−3.91, −0.23
Vitamin C administered as the only intervention
Yes	16	−2.59	−3.81, −1.38	0.06	16	−0.52	−2.07, 1.04	0.12
No	15	−4.98	−7.30, −2.65		13	−2.73	−5.03, −0.42
Antihypertensive medication use
Yes	15	−3.58	−5.78, −1.37	0.79	14	−0.78	−2.68, 1.12	0.41
No	16	−3.93	−5.86, −2.00		15	−2.01	−3.84, −0.18
No. of BP measurements
1–2	10	−4.02	−5.57, −2.47	0.01	10	−2.37	−4.64, −0.10	0.05
3–4	10	−3.46	−6.01, −0.90		8	−1.28	−2.90, 0.35
60–66 (ABPM)	3	−1.69	−2.75, −0.62		3	1.38	−1.17, 3.93
Trial size
<38 participants	14	−2.76	−4.60, −0.91	0.12	12	0.49	−1.48, 2.47	0.01
≥38 participants	17	−4.68	−6.74, −2.63		17	−2.69	−4.49, −0.88

¹If a trial reported effects in 2 distinct subgroups, it was counted twice. As a result, the total number may exceed the 29 trials included in the primary analysis. P represents whether or not the groups were different and was determined by meta-regression of the subgroups. ABPM, ambulatory blood pressure monitoring; BP, blood pressure; DBP, diastolic blood pressure; SBP, systolic blood pressure.