Table 2.
Sample characteristics and breast milk iodine concentration by maternal characteristics in lactating women (n = 175).
| Characteristics | Mean (±SD) | BMIC Median | p-Value a |
|---|---|---|---|
| Age mother, years | 32 ± 4.2 | ||
| Infant age, weeks | 11 ± 6.6 | ||
| BMI, kg/m2 | 25 ± 4.7 | ||
| Maternal age, categories | n (%) | ||
| ≤30 years | 66 (37.7) | 66 | 0.220 |
| >30 years | 109 (62.3) | 69 | |
| Infant age, categories | |||
| 2–10 weeks | 89 (50.9) | 70 | 0.034 |
| 11–19 weeks | 54 (30.9) | 71 | |
| 20–28 weeks | 32 (18.3) | 48 | |
| BMI categories | |||
| <24.9 | 108 (61.7) | 69 | 0.098 |
| ≥25–29.9 | 47 (26.9) | 52 | |
| ≥30 | 20 (11.4) | 84 | |
| Number of children | |||
| One child | 106 (60.6) | 70 | 0.382 |
| More than one child | 69 (39.4) | 66 | |
| Lactation | |||
| Exclusive breastfeeding | 140 (80.0) | 80 | 0.096 |
| Partial breastfeeding | 35 (20.0) | 66 | |
| Education | |||
| ≤12 years (high school) | 32 (18.3) | 52 | 0.487 |
| 1–4 years higher education | 53 (30.3) | 70 | |
| >4 years of higher education | 90 (51.4) | 68 | |
| Country of birth | |||
| Norway | 113 (64.6) | 68 | 0.414 |
| Other | 62 (35.4) | 64 | |
| HDI birth country b | |||
| Very high HDI | 134 (76.6) | 67 | 0.808 |
| High HDI | 13 (7.4) | 70 | |
| Medium HDI | 11 (6.3) | 75 | |
| Low HDI | 17 (9.7) | 71 | |
| Smoking | |||
| No | 170 (97.1) | 68 | 0.305 |
| Daily | 5 (2.9) | 57 | |
| Thyroid disease | |||
| No | 164 (93.7) | 67 | 0.130 |
| Yes c | 11 (6.3) | 82 | |
| Iodine supplement use habitually | |||
| No | 124 (70.9) | 60 | <0.001 |
| Yes | 51 (29.1) | 99 | |
| Iodine supplement use last 24 h | |||
| No | 144 (82.3) | 61 | <0.001 |
| Yes | 31 (17.7) | 140 |
a p-value for difference between groups using Mann-Whitney U-test (two groups) or Kruskall Wallis test (more than two groups); b HDI: Human Development Index, includes country of origin of all study participants; c Includes both hypothyroidism (10 women) and hyperthyroidism (one woman). BMIC: iodine concentrations in breast milk; BMI: body mass index.