Table 4 Pooled estimates of Vitamin D on T2DM biomarkers according to SMD analysis

Vit D supplementation on FBS levels

Total

17

− 0.26 (− 0.38, − 0.14)

 < 0.001

67.6

 < 0.001

Sample size

 ≤ 500

8

− 0.36 (− 0.60, − 0.12)

0.004

59.0

0.017

500–1000

2

− 0.20 (− 0.43, 0.03)

0.096

54.7

0.137

 > 1000

5

− 0.17 (− 0.38, 0.05)

0.123

79.3

0.001

NR

2

− 0.36 (− 0.54, − 0.18)

 < 0.001

0.0

0.501

Age (year)

 ≤ 50

8

− 0.44 (− 0.62, − 0.26)

 < 0.001

41.7

0.100

 > 50

4

− 0.14 (− 0.31, 0.03)

0.116

59.8

0.059

NR

5

− 0.17 (− 0.36, 0.02)

0.086

65.8

0.020

Gender

Women

7

− 0.38 (− 0.49, − 0.28)

 < 0.001

0.0

0.835

Both

10

− 0.17 (− 0.33, − 0.01)

0.035

70.6

 < 0.001

Health condition

GDM

3

− 0.43 (− 0.62, − 0.25)

 < 0.001

0.0

0.657

PCOS

3

− 0.38 (− 0.55, − 0.22)

 < 0.001

0.0

0.508

NAFLD

1

− 0.23 (− 0.88, 0.42)

0.488

–

–

T2DM and Non-obese

4

− 0.15 (− 0.46, 0.16)

0.330

83.0

 < 0.001

Overweight and Obese

2

− 2.20 (− 6.95, 2.55)

0.365

85.5

0.009

Dialysis patients

1

− 1.13 (− 2.15, − 0.11)

0.030

–

–

Prediabetics

2

− 0.28 (− 0.57, 0.01)

0.056

75.2

0.044

Diabetic Nephropathy

1

− 0.05 (− 0.29, 0.19)

0.689

–

–

Duration (week)

 ≤ 15

8

− 0.34 (− 0.55, − 0.13)

 < 0.001

60.6

0.013

 > 15

6

− 0.10 (− 0.25, 0.05)

0.196

63.4

0.018

NR

3

− 0.39 (− 0.54, − 0.24)

 < 0.001

0.0

0.658

Dose (IU/day)

 ≤ 4000

6

− 0.22 (− 0.42, − 0.03)

0.024

73.0

0.002

 > 4000

7

− 0.25 (− 0.48, − 0.02)

0.030

75.2

 < 0.001

NR

4

− 0.36 (− 0.53, − 0.20)

 < 0.001

0.0

0.400

Vit D supplementation on HbA1c levels

Total

13

− 0.16 (− 0.27, − 0.05)

0.004

74.0

 < 0.001

Sample size

 ≤ 500

4

− 0.12 (− 0.34, 0.11)

0.310

54.8

0.084

500–1000

2

− 0.16 (− 0.50, 0.18)

0.364

92.1

 < 0.001

 > 1000

5

− 0.14 (− 0.28, 0.00)

0.052

77.7

 < 0.001

NR

2

− 1.07 (− 1.71, − 0.42)

 < 0.001

0.0

0.815

Age (year)

 ≤ 50

2

− 0.35 (− 0.49, − 0.20)

 < 0.001

0.0

0.858

 > 50

5

− 0.15 (− 0.28, − 0.02)

0.024

68.9

0.012

NR

6

− 0.09 (− 0.31, 0.13)

0.414

75.0

 < 0.001

Gender

Women

4

− 0.47 (− 0.91, − 0.03)

0.035

49.2

0.117

Both

9

− 0.12 (− 0.23, − 0.02)

0.024

76.3

 < 0.001

Health condition

GDM

3

− 0.31 (− 0.59, − 0.03)

0.029

5.0

0.349

T2DM and Non-obese

6

− 0.16 (− 0.35, 0.02)

0.088

83.4

 < 0.001

Prediabetics

2

− 0.26 (− 0.63, 0.11)

0.165

81.1

0.019

Diabetic Nephropathy

1

0.01 (− 0.09, 0.11)

0.845

–

–

obese

1

− 0.16 (− 0.45, 0.13)

0.280

–

–

Duration (week)

 ≤ 15

4

− 0.25 (− 0.38, − 0.12)

 < 0.001

34.7

0.204

 > 15

6

− 0.04 (− 0.14, 0.06)

0.476

63.1

0.019

NR

3

− 0.67 (− 1.09, − 0.25)

0.002

24.9

0.264

Dose (IU/day)

 ≤ 4000

7

− 0.15 (− 0.32, 0.01)

0.069

83.2

 < 0.001

 > 4000

3

− 0.12 (− 0.19, − 0.06)

 < 0.001

0.0

0.702

NR

3

− 0.62 (− 1.47, 0.24)

0.157

64.8

0.058

Vit D supplementation on HOMA− IR levels

Total

19

− 0.31 (− 0.46, − 0.16)

 < 0.001

75.9

 < 0.001

Sample size

 ≤ 500

9

− 0.44 (− 0.71, − 0.17)

 < 0.001

65.4

0.003

500–1000

5

− 0.13 (− 0.35, 0.08)

0.213

68.1

0.014

 > 1000

2

− 0.29 (− 0.47, − 0.11)

 < 0.001

0.0

0.392

NR

3

− 0.43 (− 0.97, 0.11)

0.118

81.9

0.004

Age (year)

 ≤ 50

9

− 0.25 (− 0.42, − 0.08)

0.004

53.5

0.028

 > 50

2

− 0.43 (− 0.68, − 0.18)

 < 0.001

0.0

0.555

NR

8

− 0.33 (− 0.62, − 0.04)

0.027

86.9

 < 0.001

Gender

Women

6

− 0.35 (− 0.60, − 0.09)

0.009

54.4

0.052

Both

13

− 0.30 (− 0.48, − 0.12)

 < 0.001

80.4

 < 0.001

Health condition

GDM

2

− 0.57 (− 0.89, − 0.24)

 < 0.001

0.0

0.605

PCOS

3

− 0.17 (− 0.36, 0.02)

0.082

4.6

0.350

Prediabetes

2

− 0.29 (− 0.47, − 0.11)

 < 0.001

0.0

0.392

T2DM

7

− 0.40 (− 0.73, − 0.07)

0.019

88.8

 < 0.001

NAFLD

2

− 1.43 (− 2.31, − 0.55)

 < 0.001

0.0

0.614

Overweight and obese

3

− 0.10 (− 0.23, 0.03)

0.116

0.0

0.442

Duration (week)

 ≤ 15

8

− 0.44 (− 0.72, − 0.17)

0.002

68.5

0.002

 > 15

7

− 0.15 (− 0.32, 0.02)

0.087

57.1

0.030

NR

4

− 0.38 (− 0.74, − 0.03)

0.035

80.3

0.002

Dose (IU/day)

 ≤ 4000

8

− 0.37 (− 0.64, − 0.10)

0.007

84.4

 < 0.001

 > 4000

7

− 0.21 (− 0.37, − 0.05)

0.009

21.6

0.264

NR

5

− 0.48 (− 0.94, − 0.02)

0.039

81.8

 < 0.001

Vit D supplementation on Insulin levels

Total

12

− 0.33 (− 0.56, − 0.11)

0.004

81.8

 < 0.001

Sample size

 ≤ 500

8

− 0.80 (− 1.58, − 0.02)

0.045

82.6

 < 0.001

 > 500

2

− 0.24 (− 0.59, 0.11)

0.185

82.5

0.017

NR

2

− 0.12 (− 0.34, 0.09)

0.273

87.6

0.005

Age (year)

 ≤ 50

8

− 0.57 (− 1.01, − 0.13)

0.010

83.8

 < 0.001

 > 50

1

− 0.84 (− 1.67, − 0.00)

0.049

–

–

NR

3

− 0.03 (− 0.12, 0.06)

0.497

0.0

0.718

Gender

Women

5

− 0.85 (− 1.69, − 0.02)

0.046

86.7

 < 0.001

Both

7

− 0.20 (− 0.39, 0.00)

0.053

74.7

 < 0.001

Health condition

GDM

2

− 2.13 (− 5.90, 1.64)

0.268

95.5

 < 0.001

PCOS

3

− 0.29 (− 0.62, 0.05)

0.091

26.6

0.256

Diabetes

2

− 0.32 (− 1.10, 0.47)

0.428

73.2

0.053

NAFLD

2

− 1.04 (− 2.14, 0.05)

0.061

49.6

0.159

Dialysis Patients

1

1.32 (− 0.15, 2.79)

0.078

–

–

Overweight and Obese

1

− 0.07 (− 0.23, 0.09)

0.406

–

–

Prediabetes

1

− 0.23 (− 0.34, − 0.13)

 < 0.001

–

–

Duration (week)

 ≤ 15

7

− 0.75 (− 1.46, − 0.04)

0.039

84.9

 < 0.001

 > 15

5

− 0.15 (− 0.30, 0.01)

0.064

68.4

0.013

Dose (IU/day)

 ≤ 4000

7

− 0.47 (− 0.80, − 0.14)

0.005

86.6

 < 0.001

 > 4000

4

− 0.13 (− 0.55, 0.29)

0.543

46.0

0.135

NR

1

− 0.25 (− 1.02, 0.52)

0.527

–

–