Iodine

Iodine is an essential micronutrient for the proper functioning of the thyroid and the synthesis of thyroid hormones, namely triiodothyronine, (T3) and thyroxine (T4), which contain respectively 3 and 4 iodine atoms in their molecule.

Thyroid hormones are fundamental for many metabolic functions involving different organs and systems, at all stages of life, starting from the intrauterine one.

An insufficient intake of iodine to the developing fetus, due to inadequate intake by the pregnant woman, has dramatic effects especially on the central nervous system, leading to situations of severe mental retardation (cretinism), as well as metabolic disorders and deficits of various kinds.

Later, iodine deficiency or insufficiency can have more or less relevant effects on the cardiovascular, neurological and musculoskeletal level, also being at the origin of most thyroid diseases, first of all the goiter (the well-known swelling that appears in the anterior and central area of the neck, due to the enlargement of the gland).

Meeting the daily iodine requirement should, therefore, be a nutritional priority for everyone, regardless of age and the presence of other diseases. Yet the attention that most people continue to pay to this element remains quite low, with the result that, despite numerous awareness campaigns and government initiatives, there are still many damages from iodine deficiency or insufficiency found, not only in areas far from the sea or characterized by low standards of nutrition, but also in Western countries, Italy included.

What it is, how to take it

Iodine is a key component of several minerals. It is found in small quantities in marine waters in the form of iodide (negatively charged ion) and is abundant in some salt deposits, in this case in the form of sodium iodate.

The main source of natural iodine accessible to humans is represented by food, the content of which may depend on the characteristics of the soil in which they are grown (vegetables and fruits), the fortification with iodine of feed for the nutrition of animals intended for food (milk and dairy products, meat), the environment in which marine fish, crustaceans and mussels (caught or farmed) live.

The foods naturally characterized by a higher iodine content and able to ensure a greater intake in relation to the average quantities consumed with the diet are fish and derived fish products, dairy products and milk (the latter the main source of iodine for newborns and in the first years of life).

Fish and shellfish contain on average 10-140 micrograms (μg) per 100 g, milk and its derivatives 15-60 μg/100 g, eggs 50 μg/100 g, meat and cereals 5-30 μg/100 g.

Marine algae, whose consumption has become widespread in recent years, is also an important source of iodine: the content of this element can exceed 200-250 μg per 1 g in species that are richer in it. For this reason, seaweed should be taken in very small quantities and the consumption of variants such as Fucus, Kelp and Kombu is not recommended for those suffering from hyperthyroidism (due to excessive functioning of the gland) or Hashimoto’s thyroiditis (autoimmune thyroid disease, very common especially among women after 35-40 years).

To determine the actual dietary intake of iodine also contributes the method of preparation of food: frying and grilling are the most “respectful”, subtracting respectively 20% and 23% of the initial iodine content of raw food, while boiling comes to take as much as 58%, impoverishing many dishes based on vegetables and fish, unless you also use the broth.

The amount of iodine taken with food is also linked to the content of this element in fertilizers, feed, irrigation products, iodophores (compounds present in disinfectants used to clean the teats with which milk is expressed in farms) and erythrosine (a dye, E127, added to candies, drugs and some industrial foods).

Other minor sources of iodine include tablets used for water purification, contrast media used in radiology and certain medications (for example, amiodarone, the active ingredient used to treat atrial fibrillation).

Iodine absorption and metabolism

Dietary iodine is absorbed by the intestine in an average share of more than 90% of the total ingested. Under conditions of adequate dietary intake, the body contains about 15-20 mg of iodine mainly in organic form, most of which is concentrated in the thyroid where it is used for the production of thyroid hormones. The rest is found in tissues. The elimination is almost entirely urinary.

According to official estimates and recommendations, the daily intake levels of iodine of the adult organism (male and female) is about 150 μg/day and rises to 200 μg/day in pregnant and lactating women. In children, however, it varies according to age:

To meet the metabolic needs of iodine, in addition to choosing foods that contain higher amounts and cooking them in order to preserve its content, it is advisable to pay attention to foods that can interfere with its transport within the thyroid, such as turnips, broccoli, cabbage, horseradish, soy , spinach, rapeseed and certain food additives. In conditions of adequate iodine intake, an “average” consumption of these “interfering” foods does not create problems, while it may be contraindicated in the presence of thyroid diseases or iodine deficiency states.

In addition, it should be remembered that the presence of deficits of other essential micronutrients, such as selenium, exacerbates the state of iodine deficiency since it is involved in the metabolism of thyroid hormones.

The likelihood of taking too much iodine and experiencing damage from chronic toxicity is remote. According to the LARN the intake limit for iodine is 600 mg for the adult.

Meeting iodine requirements with food

Epidemiological data and clinical experience clearly indicate that iodine taken with common foods is generally not sufficient to meet the daily requirement necessary for maintaining normal thyroid activity.

Although the average iodine intake of the Italian population has improved considerably in recent years, our country remains an area of partial iodine-insufficiency. To prove it is the persistence of goiter in about 10% of the population.

Currently, the easiest, most effective and cost-effective way to prevent and correct iodine deficiency disorders is to regularly use iodine-fortified salt (available as potassium iodide, KI, or as potassium iodate, KIO3) instead of common table salt (sodium chloride, NaCl). The importance of this preventive measure is such that the sale of iodized salt in Italy was made mandatory with Law no. 55/2005, “Provisions aimed at the prevention of endemic goiter and other iodine deficiency diseases”.

According to this law, iodized salt available in common sales channels (retail stores, large retailers, pharmacies and parapharmacies, specialty nutrition stores, etc.) must contain at least 30 mg of iodine per kg of table salt.

It should be emphasized that the invitation to consume iodized salt to ensure the proper functioning of the thyroid is not at odds with the recommendation to limit the use of salt in order to reduce the risk of hypertension and other cardiovascular diseases. Consumption of iodized salt in line with the indication not to exceed 5 g / day of salt in adults and 2-3 g / day in children allow, in fact, to guarantee an iodine intake of more than 150 μg / day in adults and 100-125 μg / day in children.

In children, 2-3 g / day of iodized salt are sufficient to ensure an optimal intake of iodine in view of the greater consumption of milk typical of this age group: taking 200 ml of milk a day allows, in fact, to satisfy about 30% of the daily requirement of iodine in childhood, thanks to the high amount of this element present in the feed administered to livestock.

Another important contribution to ensuring an adequate iodine intake in all age groups comes from iodine-enriched vegetables, such as potatoes and carrots. Enrichment can increase up to ten times the iodine content of vegetables (from 2-3 to 20-30 μg per 100 grams of food) and their regular consumption in place of unenriched versions can increase iodide (concentration of iodine in the urine, used as a parameter to evaluate its intake) by 20%.

Alternative iodine supplementation strategies, tested with varying success in different parts of the world and less exploited, include the administration of iodized oil orally or subcutaneously, the iodation of water (implemented in China), the addition of iodine to bread or iodide to chocolates (to entice children more). Among the Italian experiences, it is worth mentioning the iodine supplementation by subcutaneous injection carried out in sheep farms in Abruzzo which, in addition to increasing the concentration of iodine in meat, has led to an improvement in animal fertility.

Iodine and food supplements

Like almost all essential or useful micronutrients, but present in modest quantities in the common diet, iodine can also be taken through food supplements that generally take the form of the aforementioned seaweed (considered to all intents and purposes natural iodine supplements) or multivitamin and multi-mineral preparations with variable composition.

In this regard, it should be noted that, according to what is established by the Ministry of Health, in order to be defined as a “food supplement”, a product must ensure a minimum intake of the active compound of interest with the daily intake dose indicated on the label not less than 15% of the recommended daily intake (RDA).

For some of the components of a dietary supplement, maximum contents are also provided, established to ensure safe consumption and avoid the risk of overdose, in the context of an average diet. In the case of iodine, the upper limit per daily dose of supplement is 225 μg: therefore, any multivitamin preparation cannot contain more than this.

A simple rule to avoid the remote risk of taking an excessive amount of iodine is not to use iodized salt during periods of intake of multivitamin supplements also containing iodine or especially if you regularly consume seaweed (for example, added to salads, soups or oriental dishes). In essence, supplementing iodine is important and recommended, but you should not add up too many supplements at once.