Characteristics of the study population at age 6–7 years, compared with the KOALA birth cohort and the cohort that provided biosamples
| KOALA birth cohort (N=2834) | Cohort with biosamples (N=1356) | Study cohort at 6–7 years (N=436) | |
| Recruitment group conventional | 2343 (82.7%) | 975 (71.9%) | 380 (87.2%) |
| Maternal age at delivery (mean±SD) | 32.0±3.8 | 32.6±3.9 | 32.4±3.6 |
| Maternal education* | |||
| Low | 289 (10.3%) | 101 (7.5%) | 33 (7.6%) |
| Middle | 1060 (37.9%) | 464 (34.5%) | 169 (39.1%) |
| High | 1341 (47.9%) | 737 (54.9%) | 218 (50.5%) |
| Other | 108 (3.9%) | 41 (3.1%) | 12 (2.8%) |
| Maternal smoking during early pregnancy† | |||
| Yes | 200 (7.1%) | 66 (4.9%) | 19 (4.4%) |
| Maternal smoking during late pregnancy‡ | |||
| Yes | 208 (7.3%) | 70 (5.2%) | 22 (5.0%) |
| Maternal alcohol use during early pregnancy† | |||
| Yes | 300 (14.6%) | 163 (13.8%) | 46 (12.5%) |
| Maternal alcohol use during late pregnancy‡ | |||
| Yes | 468 (16.5%) | 254 (18.7%) | 70 (16.1%) |
| Maternal BMI before pregnancy (mean±SD) | 23.6±4.0 | 23.4±3.8 | 23.8±3.7 |
| Gender | |||
| Boy | 1448 (51.2%) | 689 (50.9%) | 198 (45.4%) |
| Birth weight | |||
| <2500 g | 79 (2.8%) | 18 (1.3%) | 3 (0.7%) |
| 2500–4500 g | 2663 (94.7%) | 1288 (95.6%) | 417 (95.6%) |
| >4500 g | 70 (2.5%) | 41 (3.0%) | 16 (3.7%) |
| BMI of child at 2 years (mean±SD) | 16.4±1.4 | 16.4±1.4 | 16.6±1.4 |
| Use of multivitamins/minerals at age 2 years | |||
| Yes | 369 (14.3%) | 202 (16.2%) | 68 (15.7%) |
| Exposure to environmental tobacco smoke in first 6–7 years of life | |||
| Yes | 485 (24.7%) | 178 (17.7%) | 71 (16.3%) |
| Physical activity at age 4–5 years (mean±SD)§ | 13.2±6.3 | 13.0±6.4 | 13.4±6.4 |
| Physical activity at age 6–7 years (mean±SD)§ | 15.3±6.9 | 13.8±6.2 | 14.6±6.3 |
| Maternal plasma level 25(OH)D (mean±SD)¶ | 43.8±18.2 | 43.8±18.2 | 46.0±18.2 |
| Child's plasma level 25(OH)D (mean±SD)** | 72.0±21.6 | 72.1±21.6 | 73.1±22.0 |
| Vitamin D dosage/day during pregnancy | |||
| 0 μg | 1080 (38.1%) | 533 (39.3%) | 177 (40.6%) |
| <10 μg | 346 (12.2%) | 203 (15.0%) | 38 (8.7%) |
| ≥10 μg | 1408 (49.7%) | 620 (45.7%) | 221 (50.7%) |
| Period of multivitamin use during pregnancy†† | |||
| No | 1080 (38.1%) | 533 (39.3%) | 177 (40.6%) |
| First trimester | 359 (12.7%) | 200 (14.8%) | 54 (12.4%) |
| Second and/or third trimester | 706 (24.9%) | 284 (21.0%) | 86 (19.7%) |
| All trimesters | 686 (24.2%) | 337 (24.9%) | 119 (27.3%) |
| Duration of multivitamins during pregnancy †† | |||
| No | 1080 (38.1%) | 533 (39.3%) | 177 (40.6.%) |
| One trimester | 388 (13.7%) | 198 (14.6%) | 57 (13.1%) |
| Two trimesters | 677 (23.9%) | 286 (21.2%) | 83 (19.0%) |
| All trimesters | 686 (24.2%) | 337 (24.9%) | 119 (27.3%) |
| Vitamin D supplement use at age 1 year | |||
| Yes | 1286 (50.1%) | 584 (45.5%) | 221 (50.8%) |
| Vitamin D supplement use at age 2 years | |||
| Yes | 1920 (74.5%) | 890 (71.3%) | 331 (76.4%) |
| Vitamin D dosage/day at age 6–7 years | |||
| 0 μg | 310 (71.6%) | ||
| >0–≤2.5 μg | 82 (18.9%) | ||
| ≥2.5 μg | 41 (9.5%) | ||
Numbers do not always add up to the total because of missing data.
↵* Low: primary school, preparatory vocational or lower general secondary school, middle: vocational, higher general secondary or pre-university education, high: higher vocational or academic education.
↵† Early pregnancy: 14th week of pregnancy.
↵‡ Late pregnancy: 34th week of pregnancy.
↵§ In hours/week based on questionnaires.
↵¶ Measurement during 36th week of pregnancy.
↵** Measurement at age 2 years.
↵†† Vitamin D containing multivitamin supplements.