Table 1. Characteristics of 975 Participants in the Vitamin D Intervention in Infants Studya.
| Characteristic | All (N = 975) | 400-IU Group (n = 489) | 1200-IU Group (n = 486) |
|---|---|---|---|
| Child | |||
| Sex, female, No. (%) | 485 (49.7) | 242 (49.5) | 243 (50.0) |
| Birth weight, mean (SD), g | 3539 (395) | 3514 (379) | 3565 (410) |
| Birth length, mean (SD), cm | 50.3 (1.7) | 50.3 (1.7) | 50.4 (1.8) |
| Apgar score at 1 min, mean (SD) | 9 (1) | 9 (1) | 9 (1) |
| Gestational age, mean (SD), wk | 40.2 (1.1) | 40.1 (1.1) | 40.2 (1.1) |
| Mode of birth, vaginal, No. (%) | 911 (93.4) | 456 (93.3) | 455 (93.6) |
| Season of birth, No. (%) | |||
| Winter | 189 (19.4) | 100 (20.4) | 89 (18.3) |
| Spring | 400 (41.0) | 197 (40.3) | 203 (41.8) |
| Summer | 217 (22.3) | 108 (22.1) | 109 (22.4) |
| Autumn | 169 (17.3) | 84 (17.2) | 85 (17.5) |
| Older siblings (n = 892), No. (%) | 331 (37.1) | 153 (34.5) | 178 (39.7) |
| Breastfeeding (n = 854), No. (%) | |||
| 0-3 mo | 72 (8.4) | 39 (9.1) | 33 (7.7) |
| 3.1-6 mo | 108 (12.6) | 59 (13.8) | 49 (11.5) |
| >6 mo | 674 (78.9) | 330 (77.1) | 344 (80.8) |
| Daily dietary intake of vitamin D at age 12 mo (n = 730), mean (SD), IU | 248 (148) | 252 (144) | 240 (148) |
| Daily dietary intake of calcium at age 12 mo (n = 730), mean (SD), mg | 613 (308) | 627 (310) | 599 (307) |
| Day care attendance, No. (%) | |||
| At age 12 mo (n = 866) | 38 (4.4) | 15 (3.4) | 23 (5.3) |
| At age 24 mo (n = 796) | 491 (61.7) | 243 (61.4) | 248 (62.0) |
| Age at baseline, mean (SD), mo | 16.3 (3.4) | 16.3 (3.5) | 16.3 (3.3) |
| Influenza vaccination (n = 889), No. (%) | 353 (39.7) | 190 (42.7) | 163 (36.7) |
| Mother | |||
| Age at delivery, mean (SD), y | 31.5 (4) | 31.2 (4) | 31.8 (5) |
| BMI before pregnancy (n = 891), mean (SD) | 23.2 (3.7) | 23.1 (3.7) | 23.3 (3.7) |
| Use of vitamin D supplements during pregnancy (n = 863), No. (%) | 813 (94.2) | 407 (94.7) | 406 (93.7) |
| Daily vitamin D supplemental dose during pregnancy (n = 863), IU, mean (SD) | 620 (640) | 660 (760) | 580 (520) |
| Socioeconomic | |||
| Maternal educational level (n = 883), No. (%)b | |||
| Low | 226 (25.6) | 119 (27.2) | 107 (24.0) |
| High | 657 (74.4) | 318 (72.8) | 657 (76.0) |
| Paternal educational level (n = 870), No. (%)b | |||
| Low | 328 (37.7) | 164 (37.8) | 164 (37.6) |
| High | 542 (62.3) | 270 (62.2) | 272 (62.4) |
| Household annual income (n = 750), No. (%)c | |||
| Low | 135 (18.0) | 64 (16.8) | 71 (19.2) |
| Medium | 544 (72.5) | 281 (73.9) | 263 (71.1) |
| High | 71 (9.7) | 35 (9.2) | 36 (9.7) |
| Maternal smoking before pregnancy (n = 878), No. (%) | 130 (14.8) | 64 (14.8) | 66 (14.8) |
| Maternal smoking after delivery (n = 869), No. (%) | 32 (3.7) | 17 (4.0) | 15 (3.4) |
| Mother or father smoking after delivery (n = 837), No. (%) | 137 (16.4) | 65 (15.7) | 72 (17.0) |
Abbreviation: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared).
a
Infants were randomized to receive vitamin D3, 400 IU/d or 1200 IU/d.
b
For educational level, low indicates less than a bachelor’s degree; high, at least a bachelor’s degree.
c
For annual income, low indicates less than €40 000 (<$48 316); medium, €40 000 to €109 999 ($48 316-$132 868); and high, €110 000 ($132 869) or more.