Recommended Dietary Allowance (RDA) for Iodine
The recommended dietary allowance (RDA) for iodine is 150 μg/day for adults, 220 μg/day for pregnant women, and 290 μg/day for lactating women according to the World Health Organization (WHO) and most international guidelines. 1, 2
Age-Specific Iodine Requirements
Iodine requirements vary by age and physiological state:
| Age Group | WHO/FAO Recommendation | US IoM | EFSA | UK DoH |
|---|---|---|---|---|
| Preschool children (0-59 months) | 90 μg/day | 90 μg/day | 70-90 μg/day | 60-70 μg/day |
| School children (6-12 years) | 120 μg/day | 90-120 μg/day | 90-120 μg/day | 100-130 μg/day |
| Adolescents/Adults | 150 μg/day | 150 μg/day | 150 μg/day | 140 μg/day |
| Pregnancy | 250 μg/day | 220 μg/day | 200 μg/day | 140 μg/day |
| Lactation | 250 μg/day | 290 μg/day | 200 μg/day | 140 μg/day |
Physiological Importance of Iodine
Iodine is essential for:
- Thyroid hormone synthesis (T3 and T4)
- Regulation of metabolic rate
- Brain development, particularly during pregnancy and early childhood
- Normal growth and development
The thyroid gland stores 70-80% of the body's total 15-20 mg iodine content, with daily thyroid hormone synthesis requiring approximately 60-95 μg of iodine 2.
Consequences of Inadequate Intake
Inadequate iodine intake can lead to:
- Impaired thyroid hormone synthesis
- Hypothyroidism and goiter
- Impaired neurodevelopment in fetuses and infants
- Cognitive and neuromotor disabilities
- Increased risk of stillbirth and infant mortality
Dietary Sources of Iodine
Major dietary sources include:
- Seafood (fish, shellfish)
- Dairy products (especially cow's milk - one cup provides approximately 39% of adult needs) 3
- Iodized salt
- Eggs
It's worth noting that plant-based milk alternatives typically do not naturally contain iodine and are usually not fortified with it 3.
Special Considerations
Pregnancy and Lactation
The increased requirements during pregnancy (220-250 μg/day) and lactation (250-290 μg/day) reflect the critical role of iodine in fetal brain development and infant nutrition 1, 2.
Tolerable Upper Intake Levels
There is debate regarding the upper safe limit of iodine intake:
- European Scientific Committee on Food: 600 μg/day
- US Institute of Medicine: 1100 μg/day
Excessive iodine intake can lead to iodine-induced hyperthyroidism, particularly in older individuals with multinodular goiter or those previously exposed to iodine deficiency 4.
Supplementation Considerations
For those at risk of deficiency, particularly pregnant and lactating women:
- The American Thyroid Association recommends supplements containing 150 μg/day for all U.S. women who are pregnant, lactating, or planning pregnancy 5
- A market analysis showed that while 74.2% of adult multivitamins contained iodine (median 150 μg), only 57.6% of prenatal vitamins contained iodine 5
Public Health Implications
Universal salt iodization has been adopted by over 120 countries globally as the main method of iodine prophylaxis. However, this approach must be balanced with recommendations to reduce salt intake for cardiovascular health 1, 6.
In countries without strong iodine fortification programs, adequate iodine intake depends heavily on individual food choices, particularly consumption of iodine-rich dairy products 6.