- Iodine is an essential micronutrient.
- Iodine is known for its critical importance for the thyroid
- The soil in mid-Europe, as well as in many other countries worldwide, is considered low in iodine. Hence, it is not possible to achieve an adequate intake of iodine without dietary supplementation. Iodine is thus considered a critical micronutrient.
- Many countries have iodine supplementation programs in place using iodized salt: the US since 1923, Sweden since 1930, Finland and Austria since 1948, and Germany since the early 1980s.
- According to WHO data, around 60% of the European population does not have an adequate intake of iodine. This amounts to >40 million children and >430 million adults.
- Worldwide, WHO considers 54 countries iodine-deficient and estimates that around 2 billion people suffer from iodine deficiency (2016 data).
- Adequate iodine intake is especially important during pregnancy.
Why Do We Need Iodine?
- Essential component of the thyroid hormones, by which iodine can influence many biochemical processes in the body
- Important for energy metabolism and basal metabolism
- Helps regulate body temperature
- Important for concentration and memory
- Important for metabolism of protein, carbohydrate, and fat
- Has an antioxidant-protective function
- Supports fertility in men and women
- Important for fetal growth and development during pregnancy
- Important for mental and physical development as well as brain development in infancy
Possible Reasons for Iodine Deficiency
- Diet contains too few iodine-rich foods (see below), little or no intake of iodized salt
Increased intake requirements:
- Pregnancy, lactation, childhood
Symptoms of Deficiency
- General: signs of hypothyroidism such as weight gain, poor concentration, tiredness, sensitivity to cold, or constipation
- Thyroid: Goiter, hypothyroidism, nodules, cysts, or calcifications
- Metabolism: hyperlipidemia, sleep and cycle disorders, bradycardia
- Skin: pale, dry skin
- Hyperplasia of the mammary gland
- Fertility disorders
- Pregnancy: increase in miscarriage/stillbirth, infant mortality
- Newborns: growth disorders, brain development disorders (e.g. hearing defects)
- Recommended intake for teens and adults:
- German/Austrian/Swiss recommendation (D-A-CH): 150-200µg/day
- USA Food and Nutrition Board (FNB): 150µg/ day
- Pregnant women:
- D-A-CH recommendation: 200-230µg/day
- USA Food and Nutrition Board (FNB): 220µg/ day
- Lactating women:
- D-A-CH recommendation: 200-260µg/day
- USA Food and Nutrition Board (FNB): 290µg/day
- Children (of all ages):
- Excessive iodine intake (>500µ/day, in the USA>1,100µg/day) should be avoided as this can lead to hyperthyroidism, which can have numerous side effects.
The Best Plant Sources
The iodine content of plants depends on the iodine concentration in the soil. Many vegetables contain trace amounts of iodine, but no reliable data are available. Hence, adequate iodine intake cannot be achieved with vegetables alone. A good source of iodine is iodized table salt. In addition, algae often contain large amounts of iodine. However, the iodine content of algae can fluctuate greatly, so that many types of algae are not suitable, predictable iodine suppliers. One must also keep in mind that there are currently no generally applicable safety and nutritional standards in place for algae and algae products.
Examples of iodine content for 1g (1g!) of dried algae:
- Dulse – average 173µg, range 40-550µg/g
- Wakame – average 160µg, range 60-350µg/g
- Meeressalat – average 136µg, range 50-240µg/g
- Lithothamnium – average 45µg, range 30-60µg/g
- Nori – average 35µg, range
Other types of algae have such high levels of iodine that they should only be consumed with extreme caution. For example, algae of the genus Lamaria (includes kombu/kelp) have an average iodine content of 1,500µg/g. This corresponds to 7.5 times the recommended daily iodine intake (in one gram)! The range for kombu reaches 11,000µg/g, which is 55 times the recommended daily intake.
- Iodized salt – 20µg/g
Good to Know
One sometimes reads that certain plant-based foods, such as cruciferous vegetables, beans, soy, or millet, can influence iodine metabolism in the body and can disrupt normal thyroid function or lead to goiter. However, research indicates that thyroid function is negatively affected only when very low iodine intake is combined with excessive intake of the above foods. As long as adequate iodine intake is assured, there is no need to fear adverse effects, and the positive qualities of these foods outweighs any potential influence on the thyroid.
- Biesalski, H.K., Bischoff, S.C., Pirlich, M., Weidmann, A., (2018). Ernährungsmedizin – Nach dem Curriculum Ernährungsmedizin der Bundesärztekammer (5.Auflage). Stuttgart: Georg Thieme Verlag
- Gröber, U. (2011): Mikronährstoffe. Metabolic Tuning – Prävention – Therapie. 3. Aufl. Wissenschaftliche Verlagsgesellschaft mbH Stuttgart
- Teas J, Pino S, Crichtley A, Braverman LE. Variability of Iodine Content in Common Commercially Available Edible Seaweeds. Thyroid 2004, 14(10), 836-841