Table 5.

Subgroup analysis for SMD of circulating vitamin E level in MetS vs. control subjects.

Stratification	Number of studies	Pooled SMD	95% CI	P-value	Heterogeneity
All studies	10	−0.58	−1.04, −0.13	P = 0.01	P < 0.001; I2 = 99%
Assessment of outcome
HPLC	9	−0.24	−0.64, 0.12	P = 0.17	P < 0.001; I2 = 99%
Spectrophotometric method	1	−4.67	−5.14, −4.20	/	/
Study quality
High quality	8	−1.00	−1.54, −0.45	P < 0.001	P < 0.001; I2 = 99%
Low quality	2	0.44	−0.15, 1.02	P = 0.14	P = 0.01; I2 = 73%
Type of tocopherol
α-tocopherol	3	0.08	−0.16, 0.33	P = 0.50	P = 0.03; I2 = 72%
γ-tocopherol	2	0.54	−1.03, 2.11	P = 0.50	P = 0.004; I2 = 88%