Table 3.
Use of iodine-containing supplements in pregnancy and risk of child ADHD diagnosis (n = 77,164) 1.
| ADHD Diagnosis | ||||
|---|---|---|---|---|
| n | Crude Model | Adjusted Model 2 | Adjusted Model 2 | |
| Matched Controls | ||||
| Iodine from food <160 µg/day | ||||
| Iodine from supplement: | ||||
| No (reference) | 39,597 (11,057 3) | 1 | 1 | 1 |
| 1–200 µg/day | 16,355 | 1.03 (0.91, 1.17) | 1.13 (0.99, 1.28) | 1.01 (0.86, 1.20) |
| >200 µg/day | 1373 | 1.05 (0.71, 1.55) | 1.07 (0.72, 1.59) | 0.95 (0.63, 1.43) |
| First report of iodine 4 | ||||
| Before pregnancy 5 | 4018 | 1.02 (0.81, 1.28) | 1.24 (0.99, 1.56) | 1.11 (0.86, 1.43) |
| Gestational week 0–12 | 2970 | 1.34 (1.07, 1.68) | 1.47 (1.17, 1.85) | 1.29 (1.00, 1.67) |
| Gestational week ≥13 | 3402 | 1.04 (0.82, 1.32) | 1.11 (0.87, 1.41) | 0.98 (0.75, 1.27) |
| Iodine from food ≥160 µg/day | ||||
| Iodine from supplement: | ||||
| No (reference) | 13,763 (4152 3) | 1 | 1 | 1 |
| 1–200 µg/day | 5585 | 1.11 (0.92, 1.34) | 1.18 (0.98, 1.43) | 1.08 (0.84, 1.37) |
| >200 µg/day | 491 | 1.15 (0.66, 2.00) | 1.16 (0.66, 2.01) | 1.03 (0.58, 1.83) |
| First report of iodine 4 | ||||
| Before pregnancy 5 | 1460 | 0.97 (0.69, 1.37) | 1.21 (0.85, 1.71) | 1.09 (0.74, 1.59) |
| Gestational week 0–12 | 1020 | 1.40 (1.01, 1.95) | 1.50 (1.07, 2.10) | 1.35 (0.93, 1.96) |
| Gestational week ≥13 | 1102 | 0.99 (0.68, 1.44) | 1.04 (0.71, 1.52) | 0.93 (0.61, 1.40) |
1 Values are hazard ratios (95% CIs) unless otherwise indicated. Significant associations (p < 0.05) are highlighted. All models (including crude models) were adjusted for random effects of sibling clusters and for energy intake, to control for measurement error. Models estimating the impact of supplemental iodine (dosage and timing) included interaction terms between iodine from diet and iodine from supplements; 2 The adjusted models were additionally adjusted for maternal age, BMI, parity, education, smoking in pregnancy, fiber intake, folic acid supplement within the interval from 4 weeks beforehand to 8 weeks after conception, and total EPA and DHA intake; 3 Matched controls: controls restricted to mothers who reported the intake of supplemental vitamins and/or minerals other than the recommended; 4 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 timing of supplement use in the general questionnaires; 5 0–26 weeks before conception.