Characteristics of trials and participants included in individual participant data meta-analysis
| Study first author and year | Setting | Mean age, years (SD) [range] | Male:female | GOLD spirometric grade, N (%) | Ethnic origin | 25(OH)D assay | Mean baseline 25(OH)D, nmol/L (SD) [range] | Baseline 25(OH)D <25 nmol/L (%) | Intervention: control, all participants (participants with baseline 25(OH)D <25 nmol/L) | Oral dose of vitamin D3, intervention arm | Study duration | N with available outcome data/N randomised (%) |
| Lehouck 201213 | Secondary care, Belgium | 67.9 (8.3) [48–86] | 145:37 | 1: 2/182 (1.1). 2: 47/182 (25.8). 3: 91/182 (50.0). 4: 42/182 (23.1). | 182/182 (100.0%) white European. | RIA | 49.8 (29.2) [9.0–159.7] | 31/182 (17.0) | 91:91 (15:16) | 2.5 mg (100 000 IU) bolus monthly* | 12 months | 182/182 (100.0) |
| Martineau 201514 | Primary and secondary care, UK | 64.7 (8.5) [40–85] | 144:96 | 1: 61/240 (25.4). 2: 113/240 (47.1). 3: 52/240 (21.7). 4: 14/240 (5.8). | 227/240 (94.6%) white European† | LC-MS/MS | 46.1 (25.7) [undetectable −160.0] | 50/240 (20.8) | 122:118 (29:21) | 3 mg (120 000 IU) bolus once every 2 months‡ | 12 months | 240/240 (100.0) |
| Rafiq 201715 | Secondary care, Netherlands | 62.5 (5.6) [48–71] | 26:24 | 1: 10/50 (20.0). 2: 22/50 (44.0). 3: 13/50 (26.0). 4: 5/50 (10.0). | 49/50 (98.0%) white European§ | LC-MS/MS | 41.4 (16.0) [17.0–90.0] | 6/50 (12.0) | 24:26 (4:2) | 30 µg (1200 IU) daily | 6 months | 47/50 (94.0) |
GOLD grade 1: FEV1 ≥80% predicted; grade 2, FEV1 50.0%–79.9% predicted; grade 3, FEV1 30.0%–49.9% predicted; grade 4, FEV1 <30.0% predicted. 40 international units (IU) vitamin D3 = 1 µg; 25(OH)D concentrations reported in ng/ml were converted to nmol/L by multiplying by 2.496.
*Approximately equivalent to a daily dose of 83 µg (3320 IU) vitamin D3.
†Other participants classified ethnic origin as black African (n=1), Caribbean (n=1), Filipino (n=1), Indian (n=1), Pakistani (n=2), mixed white and Asian (n=1), mixed white and black African (n=1), mixed white and black Caribbean (n=2), Mauritian (n=1) and other (n=2).
‡Approximately equivalent to a daily dose of 50 µg (2000 IU) vitamin D3.
§Other participant classified ethic origin as Indian.
25(OH)D, 25-hydroxyvitamin D; mo, month; yr, year; wk, week. DEQAS, Vitamin D External Quality Assessment Scheme; LC-MS/MS, liquid chromatography tandem-mass spectrometry, RIA, radio-immunoassay.