What Is Iodine Deficiency? Symptoms, Treatment and Its Relationship with Breast Cancer

Iodine is a mineral essential for health. It enters the body through food or iodized table salt, is mainly taken orally and is excreted in urine.

Why does the body need iodine?

Adequate iodine is important for the healthy functioning of thyroid hormones, which regulate growth, development and energy metabolism. The thyroid gland uses iodine to produce thyroid hormones; in this sense, iodine is central to thyroid function.

• Hypothyroidism: A disease resulting from insufficient thyroid hormone at tissue level or, rarely, its ineffectiveness. Iodine deficiency also limits the thyroid's ability to produce hormones and is one cause of hypothyroidism.
• Hyperthyroidism: Excess thyroid hormone resulting from increased production by the thyroid gland. The general term for excessive thyroid hormone, regardless of its source, is thyrotoxicosis (toxic goiter).

Particularly, iodine in pregnancy requirements increase, because iodine has an important role throughout development and learning, including early brain development, and in producing hormones needed for muscle, heart and internal organ development.

Studies show that correcting iodine deficiency is a preventable cause of intellectual disability. Moderate deficiency, particularly in pregnant women and babies, is thought to have a hidden effect even on countries' development because of its adverse effects on intellectual development. Iodine deficiency is an important cause of mental developmental problems in children and has many effects in schoolchildren, including reduced reproductive function and IQ.

Why is iodine added to table salt?

Iodine deficiency and endemic goiter are important public health problems in Türkiye as worldwide. In a survey of 18 countries in the Eastern Mediterranean Region, the World Health Organization identified iodine deficiency in, out of every 3 people, 1.

Regional enlargement of the thyroid gland in people due to insufficient iodine in food, enlargement of the thyroid gland , is called endemic goiter. Between 1997-1999, the Republic of Türkiye Ministry of Health and UNICEF studied endemic goiter in 20 provincial centers, including schoolchildren aged 9-11, a total of 5948 children. The selected provinces were in previously endemic areas. Thyroid size by ultrasound and urinary iodine were measured. A substantial proportion (%31.8) had goiter, and iodine deficiency occurred in 14 provinces at moderate-to-severe levels and in all 20 provinces overall.

Following this study, legal regulations made iodization of all table salt mandatory nationwide to combat iodine deficiency and endemic goiter, and iodized salt use expanded with the 2000s.

Who is at risk of iodine deficiency?

Iodine enters the body orally. Deficiency can develop if a person does not eat iodine-rich foods or cannot obtain enough when requirements rise, such as in pregnancy. People at higher risk include:

• Pregnant women
• People living in countries with very little iodine in the soil
• People not using iodized salt 
• Vegetarian and vegan diet followers.

What are the symptoms of iodine deficiency?

Iodine deficiency mainly produces symptoms similar to thyroid hormone deficiency and hypothyroidism. Metabolism slows, less energy is produced and cell renewal slows.

• An enlarged thyroid gland and swelling at the front of the neck (goiter) 
• Weight gain
• Fatigue
• Weakness
• Hair loss
• Dry skin
• Learning and memory problems
• Feeling unable to get warm 
• Slower heart rate
• Pregnancy-related problems
• Irregular or heavier menstrual periods

What is its most important complication?

The most serious complication of iodine deficiency concerns pregnant women and their babies. It may cause problems in brain, nerve, muscle and internal organ development and intellectual disability later in life. In adults, broadly speaking, it reduces quality of life.

How are iodine deficiency or excess diagnosed?

After oral intake, iodine does not remain long in the bloodstream; it is repeatedly used in the thyroid pool, and excess is excreted in urine. Fecal excretion is approximately %2. Therefore, urinary iodine concentrations provide a good indication of iodine intake over the previous 24 hours. Accordingly, measuring urinary iodine is currently the World Health Organization's recommended method for population screening to determine iodine status.

Daily iodine requirements up to age 12 are 100-150 μg, from age 12 to adulthood >150 μg, while pregnancy and breastfeeding require >250 μg daily because needs increase. With adequate iodine, physiological adaptation occurs and sufficient thyroid hormone is produced for mother and baby.

How is iodine deficiency treated?

To maintain healthy iodine levels, 150 μg (micrograms) should be consumed daily. This meets %97-98 of iodine requirements in all healthy adults.

Which foods contain the most iodine?

There are very few "good iodine sources" in the diet, an important reason for worldwide deficiency. Because iodine is water-soluble, it is found in seawater, making seaweed (sea vegetables such as kelp) a good source. Natural sea salt may also contain traces. Iodine sources we can consume daily, their iodine content and their contribution to daily requirements are:

• Seaweed (one whole sheet) >> 1 gram contains 16 to 29 micrograms (µg) >> meets % 11-19 of the daily requirement (Gİ)
• Yogurt, plain, low-fat >> 1 cup contains 75 µg >> Gİ %50
• Iodized salt >> 1.5 gr (approximately 1/4 teaspoon) 71 µg >> Gİ %47
• Milk, low-fat >> 1 cup 56 µg >> Gİ %37 
• White bread >> 2 slices 45 µg >> Gİ %30 
• Shrimp >> 80 gr 35 µg >> Gİ %23 
• Chocolate ice cream >> 1/2 cup 30 µg >> Gİ %20 
• 1 egg >> 24 µg >> Gİ %16
• Tuna, canned in oil, drained >> 80 grams contain 17 µg >> Gİ %11
• Kashar cheese >> 30 grams contain 12 µg >> Gİ %8 
• Raisins >> 1 cup 11 µg >> Gİ %7 
• Green peas, frozen, boiled >> 1/2 cup 3 µg >> Gİ %2 
• Banana >> 1 medium 3 µg >> Gİ %2

- Daily, 1 egg, 1 cup of milk or yogurt and a quarter teaspoon of iodized salt appear to meet an adult's requirements.

Why is iodine deficiency most common in the Black Sea Region in our country?

Iodine deficiency in our country is most common in the Black Sea Region. Possible reasons include low soil iodine due to frequent rain, flooding and landslides, and frequent consumption of goitrogenic foods such as collard greens and radish. These foods may worsen existing deficiency by preventing iodine transport to the thyroid gland (false iodine deficiency). Other goitrogenic foods include soy, cauliflower, broccoli and other cruciferous vegetables.

Iodine may interact with various medicines

Studies suggest iron and vitamin A deficiencies may also have goitrogenic effects. Research on selenium and zinc's relationship with iodine continues. Iodine and iodine-containing foods may also interact with certain medicines, so caution is recommended. Examples include antithyroid medicines (methimazole), blood pressure-lowering drugs (ACE inhibitors and potassium-sparing diuretics), and psychiatric medicines containing lithium.

Is iodine deficiency associated with breast cysts and cancer?

The thyroid and breast are the body's two main iodine-retaining organs. Breast tissue has a high iodine concentration during pregnancy and particularly breastfeeding. Some studies suggest iodine supplementation may help benign breast conditions, including fibrocystic breast disease, but a specific plausible mechanism has not yet been established and data are limited. A study in the early 2000s reported lower breast cancer rates in Japanese women consuming seaweed, but excess iodine's side effects have prevented iodine from being presented as a breast cancer preventive.

The most comprehensive study of thyroid dysfunction and breast cancer risk came from Denmark in 2016. It followed 61 thousand women with hypothyroidism and 80 thousand with hyperthyroidism for breast cancer development. At the study's end, breast cancer risk was slightly lower in women with hypothyroidism and slightly higher in women with hyperthyroidism . In other words, hypothyroidism, closely associated with iodine deficiency, appears—contrary to common belief—to reduce rather than increase breast cancer risk. We therefore definitely do not recommend iodine supplements to reduce breast cancer risk in people with normal iodine levels and thyroid function.