Table 2. Follow-up Characteristics of the Participants by the Intervention Groupa.
| Characteristic | 400-IU group (n = 404), mean (SD) | No. | 1200-IU group (n = 397), mean (SD) | No. | χ2 or MD | P value |
|---|---|---|---|---|---|---|
| At 12-mo follow-up | ||||||
| Breastfed, mo | 10.5 (5.7) | 396 | 10.9 (5.6) | 392 | MD = 1.05 | .29 |
| 25(OH)D concentration | ||||||
| Mean (SD) [range], ng/mL | 33.3 (7.9) [14.8-56.0] | 373 | 46.2 (11.0) [20.7-96.4] | 373 | MD = 12.9 | <.001 |
| ≤20 ng/mL, No. (%) | 8 (2.1) | 373 | 0 | 373 | χ2 = 8.09 | .004 |
| Age at completing ASQ, mo | 11.6 (0.4) | 342 | 11.6 (0.4) | 325 | MD = 0.03 | .31 |
| ASQ total scoreb,c | 45.4 (7.3) | 336 | 46.1 (7.7) | 322 | NA | NA |
| ASQ subscale score, median (IQR) | ||||||
| Communication skills | 45 (35-50) | 337 | 45 (35-50) | 322 | NA | NA |
| Gross motor skills | 50 (35-60) | 337 | 50 (35-60) | 322 | NA | NA |
| Fine motor skills | 50 (45-60) | 341 | 50 (45-60) | 325 | NA | NA |
| Problem solving skills | 55 (45-60) | 341 | 55 (45-60) | 325 | NA | NA |
| Personal social skills | 40 (35-50) | 341 | 40 (35-50) | 325 | NA | NA |
| At 24-mo follow-up | ||||||
| 25(OH)D concentration | ||||||
| Mean (SD) [range], ng/mL | 34.8 (7.8) [17.0-61.4] | 386 | 47.3 (10.6) [22.6-83.0] | 381 | MD = 12.5 | <.001 |
| ≤20 ng/mL, No. (%) | 4 (1.0) | 386 | 0 | 381 | χ2 = 3.97 | .05 |
| Age at completing ASQ, mo | 23.5 (0.4) | 324 | 23.5 (0.4) | 312 | MD = 0.01 | .71 |
| ASQ total scoreb,c | 51.0 (5.2) | 323 | 51.3 (5.5) | 311 | NA | NA |
| ASQ subscale score, median (IQR) | ||||||
| Communication skills | 55 (50-60) | 323 | 55 (50-60) | 312 | NA | NA |
| Gross motor skills | 60 (50-60) | 324 | 60 (50-60) | 312 | NA | NA |
| Fine motor skills | 55 (50-60) | 324 | 55 (50-60) | 312 | NA | NA |
| Problem solving skills | 50 (40-55) | 324 | 50 (40-55) | 311 | NA | NA |
| Personal social skills | 50 (45-55) | 324 | 50 (45-55) | 312 | NA | NA |
| Age at completing ITSEA, mod | 25.9 (2.4) | 321 | 25.7 (2.3) | 322 | MD = −0.15 | .43 |
| ITSEA domain scoresc | ||||||
| Externalizing domain | 0.49 (0.22) | 325 | 0.51 (0.23) | 327 | NA | NA |
| Internalizing domain | 0.48 (0.22) | 325 | 0.48 (0.20) | 328 | NA | NA |
| Dysregulation domain | 0.44 (0.23) | 326 | 0.45 (0.23) | 330 | NA | NA |
| Competencies | 1.45 (0.22) | 325 | 1.45 (0.22) | 328 | NA | NA |
Abbreviations: 25(OH)D, serum 25-hydroxyvitamin D; ASQ, Ages and Stages Questionnaire; IQR, interquartile range; ITSEA, Infant-Toddler Social and Emotional Assessment; MD, mean difference; NA, not applicable.
SI conversion factor: To convert 25(OH)D to nanomoles per liter, multiply by 2.496.
a
Sample with data available on developmental milestones or social-emotional problems and competencies.
b
Total score calculated as a mean of ASQ domain scores.
c
Mean differences are shown in Tables 3 and 4.
d
Missing values are replaced with a mean of the sample in the analyses.