Table 2.
Characteristics of included infants categorized by low and high (median split) iodine (urinary concentrations, UIC) and selenium (erythrocyte concentrations, Ery-Se) status.
| Characteristics | n (% within group) and/or median (5–95th percentile) | ||||||
|---|---|---|---|---|---|---|---|
| All | UIC1 | p | Ery-Se2 | p | |||
| Infants | n = 604 | Low n = 185 | High n = 184 | Low n = 115 | High n = 114 | ||
| Birth weight (grams) | 3565 (2720–4510) | 3580 (2681–4501) | 3543 (2730–4504) | 0.281 | 3540 (2921–4568) | 3575 (2524–4455) | 0.887 |
| Missing | 6 | – | 2 | – | 1 | ||
| Sex (boy) | 280 (47) | 93 (50) | 84 (46) | 0.405f | 58 (50) | 46 (40) | 0.145f |
| Missing | 2 | – | – | – | – | ||
| Gestational age at birth (days) | 281 (260–295) | 281 (261–295) | 281 (254–295) | 0.985 | 283 (262–297) | 281 (260–294) | 0.188 |
| Missing | 5 | – | 2 | – | – | ||
| Season of birth | |||||||
| October to March | 277 (46) | 85 (46) | 89 (49) | 0.602f | 54 (47) | 37 (33) | 0.031f |
| April to September | 321 (54) | 100 (54) | 93 (51) | 61 (53) | 76 (67) | ||
| Missing | 6 | – | 2 | – | 1 | ||
| ≥1 older sibling at home (yes) | 298 (49) | 92 (50) | 90 (49) | 0.917f | 54 (47) | 54 (47) | 1.000f |
| Allergic heredity (yes) | 358 (70) | 126 (74) | 119 (68) | 0.239f | 74 (69) | 67 (62) | 0.316f |
| Missing | 90 | 14 | 8 | 8 | 6 | ||
| Allergy, 12 months (yes) | |||||||
| Food allergy | 41 (7) | 11 (6) | 14 (8) | 0.677f | 11 (10) | 7 (6) | 0.326f |
| Atopic eczema | 35 (6) | 11 (6) | 10 (5) | 1.000f | 11 (10) | 7 (6) | 0.326f |
| Asthma | 34 (6) | 11 (6) | 12 (7) | 1.000f | 3 (3) | 5 (4) | 0.724f |
| Missing3 | 105 | 18 | 12 | 12 | 8 | ||
| Breastfeeding4 | |||||||
| None | 71 (13) | 13 (7) | 34 (20) | <0.001t | 16 (14) | 17 (16) | 0.619t |
| Partially | 117 (22) | 33 (19) | 38 (23) | 27 (24) | 18 (17) | ||
| Exclusively | 342 (65) | 128 (74) | 96 (57) | 68 (61) | 73 (68) | ||
| Missing | 74 | 11 | 16 | 4 | 6 | ||
Divided into two groups with median split of urinary iodine concentrations at 4 months of age. Low includes values ≤ 113.8 μg/L and high >113.8 μg/L.
Divided into two groups with median split of erythrocyte selenium concentrations at 4 months of age. Low includes values ≤ 96.51 μg/kg and high >96.51 μg/kg.
Uncertain diagnoses were coded as missing, meaning the number of missing observations is not due to lack of data.
Extent of breastfeeding at the time of sampling (i.e., between three and 4 months of age).
Differences in distribution between low and high groups were tested with Fisher's exact test and Pearson Chi-Square for categorical variables, and Mann-Whitney U test for continuous variables.
Linear-by-Linear association.
Fisher's exact test.