Table 4.
Use of iodine-containing supplements in pregnancy and maternally reported ADHD symptoms at eight years of age (n = 27,945) 1.
| N | ADHD Score | Inattention Score | Hyperactivity Score | |||||
|---|---|---|---|---|---|---|---|---|
| Crude Model | Adjusted Model | Adjusted Model | Crude Model | Adjusted Model | Crude Model | Adjusted Model | ||
| Matched Controls 2 | ||||||||
| Iodine from food <160 µg/day | ||||||||
| Iodine from supplement: | ||||||||
| No (reference) | 14,089 (4133) | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1–200 µg/day | 6115 | 0.06 (0.04, 0.09) | 0.05 (0.03, 0.08) | 0.02 (−0.01, 0.05) | 0.06 (0.03, 0.08) | 0.05 (0.02, 0.07) | 0.06 (0.03, 0.10) | 0.06 (0.03, 0.10) |
| >200 µg/day | 457 | 0.07 (−0.00, 0.15) | 0.06 (−0.02, 0.13) | 0.02 (−0.06, 0.10) | 0.07 (−0.00, 0.15) | 0.06 (−0.02, 0.13) | 0.07 (−0.03, 0.17) | 0.06 (−0.03, 0.16) |
| First report of iodine supplement 3: | ||||||||
| Before pregnancy 4 | 1650 | 0.04 (0.00, 0.09) | 0.04 (0.00, 0.08) | 0.01 (−0.04, 0.05) | 0.06 (0.02, 0.10) | 0.05 (0.01, 0.09) | 0.02 (−0.03, 0.08) | 0.03 (−0.02, 0.08) |
| Gestational week 0–12 | 1203 | 0.12 (0.07, 0.17) | 0.10 (0.05, 0.15) | 0.06 (0.01, 0.11) | 0.11 (0.06, 0.15) | 0.07 (0.03, 0.12) | 0.14 (0.08, 0.20) | 0.13 (0.07, 0.19) |
| Gestational week ≥13 | 1264 | 0.06 (0.01, 0.11) | 0.05 (0.00, 0.10) | 0.01 (−0.04, 0.07) | 0.05 (0.01, 0.10) | 0.04 (−0.01, 0.09) | 0.07 (0.01, 0.14) | 0.07 (0.01, 0.13) |
| Iodine from food ≥160 µg/day | ||||||||
| Iodine from supplement: | ||||||||
| No (reference) | 4997 (1593) | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1–200 µg/day | 2133 | 0.02 (−0.02, 0.06) | 0.02 (−0.02, 0.07) | 0.02 (−0.04, 0.07) | 0.02 (−0.02, 0.07) | 0.02 (−0.02, 0.06) | 0.02 (−0.04, 0.07) | 0.02 (−0.03, 0.08) |
| >200 µg/day | 154 | 0.00 (−0.13, 0.14) | 0.01 (−0.11, 0.13) | 0.01 (−0.11, 0.13) | 0.02 (−0.11, 0.15) | 0.05 (−0.07, 0.17) | −0.02 (−0.20, 0.17) | −0.04 (−0.21, 0.13) |
| First report of iodine supplement 3: | ||||||||
| Before pregnancy 4 | 611 | 0.06 (−0.02, 0.13) | 0.08 (0.00, 0.15) | 0.07 (−0.02, 0.15) | 0.05 (−0.02, 0.13) | 0.06 (−0.01, 0.14) | 0.06 (−0.03, 0.16) | 0.09 (−0.00, 0.19) |
| Gestational week 0–12 | 397 | 0.03 (−0.05, 0.12) | 0.02 (−0.07, 0.10) | 0.00 (−0.09, 0.10) | 0.04 (−0.04, 0.13) | 0.02 (−0.06, 0.10) | 0.02 (−0.09, 0.13) | 0.02 (−0.09, 0.13) |
| Gestational week ≥13 | 439 | 0.02 (−0.07, 0.10) | 0.01 (−0.07, 0.09) | 0.00 (−0.09, 0.09) | 0.01 (−0.07, 0.09) | 0.00 (−0.08, 0.08) | 0.03 (−0.08, 0.14) | 0.02 (−0.09, 0.13) |
1 Values are standardized beta coefficients (95% CIs) unless otherwise indicated. Significant associations (p < 0.05) are highlighted. Models included interaction terms between iodine from diet and iodine from supplements. All models (including crude models) were adjusted for random effects of sibling clusters and for energy intake, to control for measurement error. The adjusted models were additionally adjusted for maternal age, BMI, parity, education, smoking in pregnancy, fiber intake, child sex, and birth season, folic acid supplement within the interval from 4 weeks beforehand to 8 weeks after conception, and total EPA and DHA intake; 2 Matched controls: controls restricted to mothers who reported the intake of supplemental vitamins and/or minerals other than the recommended; 3 Restricted to participants who reported taking up to 200 µg/day of supplemental iodine in the food frequency questionnaire and who also gave information on the timing of supplement use in the general questionnaires; 4 0–26 weeks before conception.