Association between Serum Vitamin C and the Blood Pressure: A Systematic Review and Meta-Analysis of Observational Studies

Table 2

The outcomes of subgroup analysis and adjustment of confounders.

Subgroups		SBP					DBP
		Studies ()	Fisher’s	95% CI	(%)		Studies ()	Fisher’s	95% CI	(%)
All studies		11	-0.17	(-0.20, -0.15)	37	0.10	10	-0.15	(-0.20, -0.10)	51	0.02
Sex	Male	5	-0.20	(-0.28, -0.12)	60	0.03	6	-0.15	(-0.24, -0.06)	65	0.01
	Female	2	-0.13	(-0.17, -0.09)	0	0.63	2	-0.12	(-0.20, -0.04)	73	0.05
Hypertension	Yes	2	-0.16	(-0.36,0.03)	86	0.008	2	-0.23	(-0.42, -0.03)	57	0.13
	No	6	-0.24	(-0.32, -0.17)	0	0.54	5	-0.20	(-0.28, -0.13)	11	0.34
Antihypertensive drugs	Unclear	4	-0.15	(-0.18, -0.12)	18	0.30	4	-0.10	(-0.14, -0.06)	0	0.69
	No	7	-0.22	(-0.27, -0.16)	14	0.32	7	-0.17	(-0.23, -0.12)	35	0.16
Level of vitamin A and vitamin E	Normal	2	-0.53	(-0.79, -0.28)	0	0.69	2	-0.26	(-0.51, -0.00)	59	0.12
	Abnormal	3	-0.19	(-0.25, -0.13)	45	0.16	3	-0.18	(-0.24, -0.12)	57	0.10
Area	America	3	-0.31	(-0.42, -0.20)	55	0.08	3	-0.23	(-0.34, -0.11)	0	0.45
	Europe	2	-0.17	(-0.21, -0.13)	0	0.67	2	-0.16	(-0.20, -0.12)	0	0.38
	Asia	6	-0.17	(-0.20, -0.13)	22	0.26	5	-0.13	(-0.20, -0.05)	61	0.02
Sample size	<100	4	-0.37	(-0.50, -0.25)	32	0.21	3	-0.16	(-0.30, -0.02)	53	0.09
	100-500	4	-0.21	(-0.28, -0.14)	0	0.99	4	-0.21	(-0.28, -0.14)	20	0.29
	>500	3	-0.16	(-0.19, -0.13)	4	0.37	3	-0.13	(-0.16, -0.10)	54	0.09
Adjusted Confounders
Age	Male	2	-0.12	(-0.17, -0.07)	75	0.04	2	-0.12	(-0.16, -0.07)	51	0.15
	Female	2	-0.10	(-0.14, -0.06)	14	0.28	2	-0.09	(-0.14, -0.05)	46	0.17
Age+sex		2	-0.11	(-0.14, -0.08)	0	0.65	2	-0.11	(-0.14, -0.08)	0	0.85
Age+BMI	Male	2	-0.11	(-0.16, -0.07)	78	0.03	2	-0.10	(-0.15, -0.06)	67	0.08
	Female	2	-0.09	(-0.13, -0.04)	0	0.52	2	-0.09	(-0.13, -0.05)	6	0.30
Age+sex+BMI		2	-0.09	(-0.12, -0.06)	0	0.50	2	-0.10	(-0.13, -0.07)	0	0.72

: value of heterogeneity.