Table 1. Participants’ baseline characteristics by allocation and overall: main trial, exercise substudy and spirometry substudy.
| Main trial | Exercise substudy | Spirometry substudy | |||||||
| Placebo | Vitamin D | Total | Placebo | Vitamin D | Total | Placebo | Vitamin D | Total | |
| N=4433 | N=4418 | N=8851 | N=330 | N=302 | N=632 | N=677 | N=666 | N=1343 | |
| Mean age, years (SD) (range) | 9.4 (1.6)(5.9–13.7) | 9.4 (1.6)(5.8–14.2) | 9.4 (1.6)(5.8–14.2) | 9.5 (1.5)(6.5–12.8) | 9.5 (1.5)(5.8–13.9) | 9.5 (1.5)(5.8–13.9) | 9.5 (1.5)(6.5–13.0) | 9.5 (1.6)(6.4–13.3) | 9.5 (1.6)(6.4–13.3) |
| Sex, n (%) | |||||||||
| Female | 2224 (50.2) | 2142 (48.5) | 4366 (49.3) | 166 (50.3) | 141 (46.7) | 307 (48.6) | 325 (48.0) | 333 (50.0) | 658 (49.0) |
| Male | 2209 (49.8) | 2276 (51.5) | 4485 (50.7) | 164 (49.7) | 161 (53.3) | 325 (51.4) | 352 (52.0) | 333 (50.0) | 685 (51.0) |
| Ethnic origin | |||||||||
| Khalkh, n (%) | 4103 (92.6) | 4062 (91.9) | 8165 (92.2) | 300 (90.9) | 275 (91.1) | 575 (91.0) | 628 (92.8) | 607 (91.1) | 1235 (92.0) |
| Other, n (%) | 330 (7.4) | 356 (8.1) | 686 (7.8) | 30 (9.1) | 27 (8.9) | 57 (9.0) | 49 (7.2) | 59 (8.9) | 108 (8.0) |
| Parental education* | |||||||||
| Secondary school or lower, n (%) | 2457 (55.4) | 2401 (54.3) | 4858 (54.9) | 201 (60.9) | 171 (56.6) | 372 (58.9) | 417 (61.6) | 398 (59.8) | 815 (60.7) |
| University/polytechnic, n (%) | 1976 (44.6) | 2017 (45.7) | 3993 (45.1) | 129 (39.1) | 131 (43.4) | 260 (41.1) | 260 (38.4) | 268 (40.2) | 528 (39.3) |
| Type of residence | |||||||||
| House with central heating, n (%) | 1083 (24.4) | 1110 (25.1) | 2193 (24.8) | 62 (18.8) | 54 (17.9) | 116 (18.4) | 100 (14.8) | 99 (14.9) | 199 (14.8) |
| Ger (Yurt), n (%) | 1628 (36.7) | 1643 (37.2) | 3271 (37.0) | 112 (33.9) | 106 (35.1) | 218 (34.5) | 277 (40.9) | 290 (43.5) | 567 (42.2) |
| House without central heating, n (%) | 1722 (38.8) | 1665 (37.7) | 3387 (38.3) | 156 (47.3) | 142 (47.0) | 298 (47.2) | 300 (44.3) | 277 (41.6) | 577 (43.0) |
| Home ownership, n (%) | |||||||||
| No | 963 (21.7) | 925 (20.9) | 1888 (21.3) | 77 (23.3) | 55 (18.2) | 132 (20.9) | 164 (24.2) | 157 (23.6) | 321 (23.9) |
| Yes | 3470 (78.3) | 3493 (79.1) | 6963 (78.7) | 253 (76.7) | 247 (81.8) | 500 (79.1) | 513 (75.8) | 509 (76.4) | 1022 (76.1) |
| Mean monthly household income, US dollars (SD)† | 845.8 (603.7) | 850.6 (553.8) | 848.2 (579.3) | 769.5 (411.6) | 844.1 (515.3) | 805.1 (465.2) | 751.5 (441.2) | 778.0 (427.8) | 764.6 (434.7) |
| Calcium intake† | |||||||||
| <500 mg/day, n (%) | 2628 (64.6) | 2599 (63.7) | 5227 (64.2) | 190 (63.8) | 179 (63.3) | 369 (63.5) | 423 (63.4) | 435 (66.1) | 858 (64.8) |
| ≥500 mg/day, n (%) | 1437 (35.4) | 1481 (36.3) | 2918 (35.8) | 108 (36.2) | 104 (36.7) | 212 (36.5) | 244 (36.6) | 223 (33.9) | 467 (35.2) |
| Mean BMI-for-age z-score (SD)† | 0.2 (1.1) | 0.2 (1.0) | 0.2 (1.1) | 0.2 (1.1) | 0.1 (1.1) | 0.2 (1.1) | 0.1 (1.0) | 0.1 (1.1) | 0.1 (1.0) |
| Mean height-for-age z-score (SD)† | −0.3 (1.0) | −0.3 (1.0) | −0.3 (1.0) | −0.3 (1.0) | −0.3 (1.1) | −0.3 (1.0) | −0.4 (0.9) | −0.3 (1.0) | −0.4 (1.0) |
| Mean serum 25(OH)D, nmol/L (SD)2 3 | 29.7 (10.5) | 29.5 (10.5) | 29.7 (10.5) | 28.6 (11.5) | 27.5 (10.5) | 28.1 (11.0) | 28.5 (10.5) | 28.1 (10.7) | 28.3 (10.6) |
| Serum 25(OH)D category†‡ | |||||||||
| <25 nmol/L, n (%) | 1424 (32.1) | 1395 (31.6) | 2819 (31.8) | 126 (38.2) | 116 (38.4) | 242 (38.3) | 253 (37.4) | 232 (34.8) | 485 (36.1) |
| 25–49.9 nmol/L, n (%) | 2809 (63.4) | 2827 (64.0) | 5636 (63.7) | 189 (57.3) | 174 (57.6) | 363 (57.4) | 399 (58.9) | 408 (61.3) | 807 (60.1) |
| 50–74.9 nmol/L, n (%) | 193 (4.4) | 187 (4.2) | 380 (4.3) | 14 (4.2) | 11 (3.6) | 25 (4.0) | 25 (3.7) | 26 (3.9) | 51 (3.8) |
| ≥75 nmol/L, n (%) | 7 (0.2) | 9 (0.2) | 16 (0.2) | 1 (0.3) | 1 (0.3) | 2 (0.3) | – | – | – |
| Mean maximal grip strength, kg (SD)† | 12.0 (4.0) | 12.0 (4.0) | 12.0 (4.0) | 12.2 (3.9) | 12.4 (3.8) | 12.3 (3.9) | 12.0 (3.9) | 12.3 (4.1) | 12.1 (4.0) |
| Mean standing long jump distance, m (SD)† | 107.9 (21.8) | 108.2 (22.6) | 108.0 (22.2) | 106.7 (21.6) | 108.8 (21.2) | 107.7 (21.5) | 107.4 (21.7) | 107.9 (23.0) | 107.6 (22.4) |
| Mean VO2peak, mL/kg/min (SD)† | – | – | – | 43.8 (3.1) | 44.2 (3.3) | 44.0 (3.2) | – | – | – |
Highest educational level attained by either parent;.
Missing values: monthly household income missing for 2 participants in the main trial (1 randomised to placebo, 1 to vitamin D); calcium intake missing for 706 participants in the main trial (368 randomised to placebo, 338 to vitamin D), 51 participants in the exercise substudy (32 randomised to placebo, 19 to vitamin D) and 18 participants in the spirometry substudy (18 randomised to placebo, 10 to vitamin D); BMI-for-age z-score missing for one1 participant in the main trial (randomised to placebo); height-for-age z-score missing for one1 participant in the main trial (randomised to placebo); 25(OH)D missing for 5 participants in the main trial (4 randomised to placebo, and 1 to vitamin D); grip strength missing for 6 participants in the main trial (2 randomised to placebo, 4 to vitamin D) and 1 participant in the spirometry substudy (randomised to placebo); long jump distance missing for 38 participants in the main trial (23 randomised to placebo, 15 to vitamin D), 2 participants in the exercise substudy (both randomised to placebo) and 3 participants in the spirometry substudy (2 randomised to placebo, and 1 to vitamin D); VO2 peak missing for 17 participants in the exercise substudy (11 randomised to placebo, and 6 to vitamin D).
Baseline 25(OH)D values deseasonalised.
BMIbody mass index25(OH)D25-hydroxyvitamin DSOSspeed of soundVO2peakpeak oxygen consumption