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Table 2 Subgroup analyses for the effect of vitamin E intake on glycemic indices and insulin resistance in patients with diabetes

From: Effect of vitamin E intake on glycemic control and insulin resistance in diabetic patients: an updated systematic review and meta-analysis of randomized controlled trials

 

Effect size, n

WMD (95% CI)a

P-within2

Ib (%)c

P-heterogeneityd

Vitamin E intake on fasting blood glucose

 Overall

34

-3.35 (-8.10, 1.40)

0.16

82.2

 < 0.001

Intervention duration (week)

  < 10

15

-6.04 (-9.88, -2.21)

0.002

19.1

0.24

  ≥ 10

19

-2.86 (-10.39, 4.66)

0.45

89

 < 0.001

Type of vitamin E

 α-tocopherol

21

-3.75 (-11.21, 3.71)

0.32

88.4

 < 0.001

 Tocoterienol

2

-4.44 (-8.91, 0.03)

0.05

0.0

0.62

 Mixed-tocopherols

1

9.00 (-14.72, 32.71)

0.45

0.0

-

 Unclear

10

-5.24 (-9.59, -0.88)

0.01

3.3

0.40

Dosage of vitamin E (mg/day)

  < 500

15

-7.13 (-14.99, 0.73)

0.07

87.3

 < 0.001

  ≥ 500

19

-0.22 (-1.73, 1.29)

0.77

0.0

0.55

Study location

 Western countries

16

-0.33 (-1.85, 1.19)

0.67

0.0

0.52

 Non-Western countries

18

-4.53 (-11.59, 2.53)

0.20

85.1

 < 0.001

Study design

 Crossover

3

-7.07 (-15.46, 1.32)

0.09

30.1

0.23

 Parallel

31

-2.82 (-8.08, 2.44)

0.29

83.4

 < 0.001

 Blinded

25

-3.96 (-9.39, 1.47)

0.15

86.5

 < 0.001

 Non-blinded

9

-2.81 (-9.62, 3.99)

0.41

0

0.49

Type of diabetes

 T2DM

27

-4.42 (-9.63, 0.76)

0.09

85

 < 0.001

 T1DM

6

0.87 (-10.53, 12.27)

0.88

0.0

0.94

 Diabetic nephropathy

1

10.00 (-5.80, 25.80)

0.21

0.0

 

Risk of bias e

 High

28

-4.10 (-9.81, 1.61)

0.16

83.2

 < 0.001

 Low

6

0.04 (-9.71, 9.78)

0.994

79.7

 < 0.001

Vitamin E intake on HbA1c

    

 Overall

36

-0.21 (-0.33, -0.09)

0.001

76.6

 < 0.001

Intervention duration (week)

  < 10

13

-0.24 (-0.48, 0.00)

0.05

75.3

 < 0.001

  ≥ 10

23

-0.24 (-0.48, 0.00)

0.01

78.2

 < 0.001

Type of vitamin E

 α-tocopherol

19

-0.18 (-0.36, 0.01)

0.06

76.3

 < 0.001

 Tocoterienol

6

-0.09 (-0.15, -0.04)

 < 0.001

0.0

0.81

 unclear

11

-0.71 (-1.21, -0.21)

0.005

86

 < 0.001

Dosage of Vitamin E (mg/day)

  ≥ 500

18

-0.41 (-0.68, -0.14)

0.003

80.2

 < 0.001

  < 500

18

-0.10 (-0.22, 0.02)

0.09

62.2

 < 0.001

Study location

 Western countries

16

-0.40 (-0.69, -0.11)

0.007

79.5

 < 0.001

 Non-Western countries

20

-0.12 (-0.24, 0.00)

0.05

66.5

 < 0.001

Study design

 Crossover

6

-0.09 (-0.15, -0.04)

0.001

0

0.54

 Parallel

30

-0.26 (-0.43, -0.10)

0.002

80.1

 < 0.001

 Blinded

27

-0.16 (-0.29, -0.04)

0.01

74.8

 < 0.001

 Non-blinded

9

-0.68 (-1.20, -0.17)

0.01

82.8

 < 0.001

Type of diabetes

 T2DM

23

-0.16 (-0.30, -0.02)

0.02

78.7

 < 0.001

 T1DM

9

-0.76 (-1.37, -0.15)

0.01

80.8

 < 0.001

 Diabetic nephropathy

2

-0.24 (-0.56, 0.07)

0.12

0

0.90

 T2DM & T1DM

1

0.00 (-0.34, 0.34)

1.00

0

-

 Diabetic neuropathy

1

-0.18 (-0.66, 0.30)

0.45

0

-

Risk of bias e

 High

30

-0.28 (-0.42, -0.13)

 < 0.001

79.4

 < 0.001

 Low

6

0.01 (-0.17, 0.18)

0.95

25.3

0.24

Vitamin E intake on fasting Insulin concentrations

 Overall

18

-1.05 (-1.53, -0.58)

 < 0.001

52.7

0.005

Intervention duration (week)

  < 10

8

-0.88 (-1.27, -0.49)

 < 0.001

0.0

0.80

  ≥ 10

10

-1.06 (-1.86, -0.26)

0.009

57.8

0.01

Type of vitamin E

 α-tocopherol

12

-0.87 (-1.60, -0.14)

0.01

53.5

0.01

 Tocoterienol

1

-0.88 (-1.33, -0.43)

 < 0.001

100

-

 Mixed-tocopherols

1

-1.40 (-5.94, 3.14)

0.54

100

-

 Unclear

4

-1.54 (-2.79, -0.29)

0.01

23.1

0.27

Dosage of Vitamin E (mg/day)

  < 500

9

-1.06 (-1.73, -0.39)

0.002

15.1

0.30

  ≥ 500

9

-1.00 (-1.68, -0.32)

0.004

66.1

0.003

Study location

 Western countries

6

-1.28 (-1.92, -0.64)

 < 0.001

61.1

0.02

 Non-Western countries

12

-0.87 (-1.56, -0.19)

0.01

35.3

0.10

Study design

 Blinded

16

-1.02 (-1.53, -0.52)

 < 0.001

56.6

0.003

 Non-blinded

2

-0.18 (-6.53, 6.18)

0.05

28.1

0.23

Type of diabetes

 T2DM

17

-1.03 (-1.55, -0.51)

 < 0.001

55.1

0.003

 Diabetic nephropathy

1

-1.20 (-2.31, -0.09)

0.03

0

-

Risk of bias e

 High

12

-1.05 (-1.85, -0.24)

0.011

44.6

0.047

 Low

6

-0.89 (-1.27, -0.51)

 < 0.001

0

0.46

Vitamin E intake on HOMA-IR

 Overall

12

-0.44 (-0.82, -0.05)

0.02

83.4

 < 0.001

Intervention duration (week)

  < 10

4

-0.18 (-0.43, 0.07)

0.15

6.5

0.36

  ≥ 10

8

-0.73 (-1.36, -0.08)

0.02

87.6

 < 0.001

Type of vitamin E

 α-tocopherol

8

-0.72 (-1.29, -0.15)

0.01

87.5

 < 0.001

 Tocoterienol

1

-0.10 (-0.39, 0.19)

0.49

0

-

 Unclear

3

0.0 (-0.57, 0.58)

0.98

0

0.67

Dosage of Vitamin E (mg/day)

  < 500

7

-0.98 (-1.83, -0.13)

0.02

88.7

 < 0.001

  ≥ 500

5

-0.17 (-0.55, 0.20)

0.36

69.5

0.01

Study location

 Western countries

2

-0.33 (-0.74, 0.08)

0.11

86.0

0.007

 Non-Western countries

10

-0.59 (-1.26, 0.08)

0.08

84.6

 < 0.001

Type of diabetes

 T2DM

11

-0.47 (-0.88, -0.05)

0.02

84.8

 < 0.001

 Diabetic nephropathy

1

-0.20 (-1.03, 0.63)

0.63

0

-

Risk of bias e

 High

7

-0.95 (-1.93, 0.02)

0.054

88.8

 < 0.001

 Low

5

-0.18 (-0.38, 0.02)

0.084

0

0.518

  1. Abbreviations: HbA1C Hemoglobin A1c, WMD weighted mean difference, HOMA-IR homeostatic model assessment for insulin resistance
  2. aObtained from the random-effects model
  3. bRefers to the mean (95% CI)
  4. cInconsistency, percentage of variation across studies due to heterogeneity
  5. dObtained from the Q-test
  6. eIf a trial had “low risk” for all domains of the Cochrane Risk of Bias Assessment tool, it was considered a high-quality study with a totally low risk of bias