Table 3 Sensitivity analysis for daily supplementation of vitamin D

Sensitivity analysis

 Daily administration [28, 29, 31, 33,34,35, 39, 40, 42, 44, 45, 50, 52, 54, 56,57,58,59,60, 62, 65, 69, 70]

23; 8788

0.94 (0.87–1.02)

0.92 (0.82–1.02)

0.92 (0.84–1.02)

0.92 (0.85–0.99)

Subgroups

 Age group (years)

  < 7 [39, 42, 52, 54, 56, 60, 69]

7; 2614

0.88 (0.79–0.99)

0.87 (0.77–0.98)

0.88 (0.78–0.98)

0.92 (0.84–1.01)

  7–17 [31, 33, 35, 44, 45, 65]

6; 1312

0.70 (0.50–1.00)

0.81 (0.64–1.03)

0.94 (0.77–1.14)

0.87 (0.67–1.12)

  18–65 [28, 29, 34, 40, 50, 57, 59, 70]

8; 2445

0.93 (0.76–1.12)

0.89 (0.72–1.11)

0.88 (0.72–1.06)

0.84 (0.70–1.02)

  > 65 [58, 62]

2; 2417

NA

NA

NA

0.91 (0.85–0.98)

 Gender proportion (%)

  Male > 60[29, 33, 44, 45]

4; 514

NA

NA

NA

0.84 (0.58–1.21)

  Male ≤ 60 [28, 31, 34, 35, 39, 40, 42, 50, 52, 54, 56,57,58,59,60, 62, 65, 69, 70]

19; 8274

0.97 (0.91–1.02)

0.95 (0.88–1.03)

0.95 (0.88–1.02)

0.92 (0.86–0.99)

 Comorbidity

  General [28, 29, 31, 35, 42, 44, 45, 52, 54, 56,57,58, 60, 62, 65, 69, 70]

17; 7078

0.95 (0.86–1.05)

0.93 (0.81–1.07)

0.94 (0.84–1.06)

0.92 (0.85–0.99)

  Disease-specific [33, 34, 39, 40, 50, 59]

6; 1710

0.70 (0.49–1.01)

0.73 (0.53–1.00)

0.75 (0.56–1.00)

0.83 (0.66–1.04)

 Baseline 25-hydroxyvitamin D levels (nmol/L)

  < 50 [35, 50, 54, 57, 70]

5; 1528

0.84 (0.64–1.10)

0.81 (0.60–1.10)

0.79 (0.53–1.20)

0.81 (0.59–1.11)

  > 50 [28, 29, 34, 39, 40, 42, 45, 52, 56, 58,59,60, 62, 65, 66]

15; 6335

0.95 (0.88–1.03)

0.94 (0.84–1.04)

0.94 (0.85–1.03)

0.93 (0.87–0.99)

 Trial duration (months)

  < 4 [28, 35, 44, 45, 57, 58, 69, 70]

8; 1792

0.90 (0.52–1.57)

0.87 (0.41–1.82)

0.87 (0.75–1.69)

0.79 (0.59–1.05)

  4–12 [29, 31, 33, 39, 42, 50, 52, 59, 60, 65]

10; 2651

0.86 (0.76–0.97)

0.84 (0.72–0.97)

0.87 (0.76–1.00)

0.89 (0.79–1.00)

  > 12 [34, 40, 54, 56, 62]

5; 4345

NA

NA

NA

0.99 (0.94–1.04)

 Climatic zone

  Tropical or Subtropical [65, 69, 70]

3; 854

NA

NA

NA

0.45 (0.14–1.48)

  Temperate [28, 29, 31, 33,34,35, 39, 40, 42, 44, 45, 50, 52, 54, 56,57,58,59,60, 62]

20; 7934

0.93 (0.86–1.00)

0.90 (0.81–0.99)

0.91 (0.82–1.00)

0.92 (0.86–0.98)

 Summer

  Summer-inclusive [34, 40, 42, 52, 54, 56,57,58,59, 62, 65, 69, 70]

13; 6824

1.00 (0.96–1.05)

1.00 (0.94–1.06)

0.98 (0.92–1.05)

0.96 (0.90–1.02)

  Summer-sparing [28, 29, 31, 33, 35, 39, 44, 45, 50, 60]

10; 1964

0.75 (0.65–0.87)

0.72 (0.60–0.85)

0.78 (0.67–0.91)

0.83 (0.69–0.99)

 Winter

  Winter-dominant [28, 29, 31, 35, 39, 44, 45, 60]

[28, 29, 31, 35, 39, 44, 45, 60]

8; 1658

0.69 (0.58–0.82)

0.70 (0.59–0.82)

0.80 (0.69–0.93)

0.78 (0.68–0.92)

  Winter-non-dominant [33, 34, 40, 42, 50, 52, 54, 56,57,58,59, 62, 65, 69, 70]

15; 7130

1.00 (0.95–1.04)

0.99 (0.93–1.06)

0.98 (0.92–1.05)

0.96 (0.89–1.02)

Sensitivity analysis

 Type of ARIs

  Mixed upper and lower respiratory tract infections [29, 33,34,35, 42, 54, 56, 60, 62, 65]

10; 4588

0.87 (0.74–1.01)

0.87 (0.74–1.01)

0.90 (0.79–1.02)

0.88 (0.80–0.97)

  Upper respiratory tract infections [28, 39, 40, 45, 50, 52, 54, 57,58,59]

10; 3254

0.91 (0.83–1.00)

0.87 (0.75–1.00)

0.87 (0.74–1.01)

0.97 (0.89–1.05)

  Lower respiratory tract infections [54]

1; 300

NA

NA

NA

0.94 (0.79–1.12)

  Influenza [31, 44, 52, 58, 59, 69]

6; 2125

0.90 (0.71–1.14)

0.87 (0.64–1.18)

0.89 (0.69–1.16)

0.94 (0.80–1.10)