Iodine plays an essential role in the synthesis of thyroid hormones necessary for normal growth, development, and metabolism. Iodine deficiency results in low thyroid hormone production which leads to poor metabolism, reduced intellectual ability, goiter (swollen neck), and many other health problems. This article is a compilation of everything you need to know about iodine deficiency. Read on to equip yourself with essential knowledge and prevention strategies.
What is the main cause of iodine deficiency?
Iodine deficiency is mainly the result of poor iodine intake through diet. According to research presented in the Proceedings of the Nutrition Society, the soil and groundwater in many parts of the world is deficient in iodine. Examples include southern Australia,the Midwest in North America, western England and Wales, and the Alpine regions of Europe, South Asia, and Southeast Asian regions. Repeated flooding and glacial activity also leach iodine out from the soil.
Moreover, the transfer of iodine from soil to plants is limited due to the strong bond that iodine shares with the soil particles. All of this contributes to low iodine concentration in plant-based food. Lack of knowledge about dietary sources of iodine is a contributing factor to iodine deficiency in many parts of the world.
Compounding this natural decline in iodine concentrations in foods is the increasing trend of consuming commercially-prepared foods. This contributes to the resurgence of mild iodine deficiency in developed countries because commercial food producers are less likely to use iodized salt.
Public health efforts to tackle the issue
Public health authorities have known about the link between iodine deficiency and goiter – the most prominent sign of iodine deficiency – since the early 20thcentury. As the link was established, worldwide public health efforts were deployed to overcome the issue of poor iodine content in food.
Universal salt iodization programs have been introduced worldwide, but the goal of 100 percent coverage is yet to be achieved. According to one estimate, 86% of the global population has access to iodized salt, but many among these people do not utilize it, and those who do, are not taking sufficient amount to meet the daily requirements.
Prevalence of iodine deficiency
More than one in four of the global population is at risk of iodine deficiency. Despite decades of effort, an estimated 2 billion people still suffer from iodine deficiency, of which 50 million have clinical manifestations, like goiter, hypothyroidism, and poor mental development.
Signs and symptoms of iodine deficiency
The most observable signs and symptoms of iodine deficiency are related to hypothyroidism, which results from poor thyroid gland function. Since iodine is an essential component of the hormones produced by the thyroid gland, any deficiency in iodine would lead to decreased production of these hormones, and hence, a set of related symptoms. The following signs and symptoms are commonly present in individuals with iodine deficiency:
- Unexplained fatigue
- Dry skin and thin hair
- Difficulty in learning and memory
- Unexplained weight loss
The most noticeable sign of iodine efficiency is goiter. It occurs due to thyroid gland enlargement secondary to iodine deficiency and presents as a swelling at the base of the neck. According to an estimate, goiter affects 25% of the iodine-deficient individuals. Besides impacting appearance, severe cases of goiter may also cause breathing and swallowing difficulties. Note that although goiter is a common manifestation of iodine deficiency, it may be due to other factors as well.
Studies suggest that more than 70% of people with low levels of thyroid hormones experience weakness and fatigue. Thyroid hormones are involved in energy production. The body produces less energy in the events of low thyroid hormone levels, leaving a person feeling weak, sluggish, and fatigued.
Many people with iodine deficiency experience hair fall and have rough, dry, and flaky skin. Some studies suggest that hair fall occurs only if the person has a relevant family history, but others suggest that up to 30% of cases with low levels of thyroid hormone experience hair fall irrespective of the family history.
While iodine deficiency during pregnancy and childhood may result in low IQ, a deficiency later in life can also cause problems with learning and memorizing. Some studies confirm that compared to individuals with optimal levels of thyroid hormone, individuals with hypothyroidism have a small hippocampus – a part of the brain associated with memory functions.
Individuals with an underactive thyroid gland are likely to gain 5-10 pounds of weight. Thyroid hormones have a major contribution to the regulation of metabolic rate. Poor thyroid function results in low metabolic rate, and hence, there are more calories to be stored.
Other signs and symptoms of iodine deficiency may include irregular periods, sensitivity to cold, and slow heartbeat.
Most individuals who use iodized salt think that they are getting enough iodine. Almost 70% of salt consumption in the United States is from commercially prepared food, which lacks in iodine. Therefore, the use of iodized salt at home is not enough to meet the daily requirements. A similar situation has been observed in Australia.
The following groups are more prone to iodine deficiency:
- Vegetarians and vegans, due to a lack of seafood consumption
- People who use non-iodized salt
- Pregnant and lactating women
- People living in areas where soil and water are deficient in iodine
- People who consume excess amounts of goitrogen-containing foods
Goitrogens are substances that interfere with the body’s utilization of iodine and are present in soy, broccoli, cabbage, cauliflower, and other cruciferous vegetables. Use of these foods in moderation does not significantly affect iodine utilization. If one does not regularly consume these foods in concentrated form (e.g. through juicing) then it’s typically not a concern.
Pregnant and lactating women require more iodine than usual. This increased demand is due to a 50% increase in production of thyroid hormones that are now also required for the growth and development of the fetus. Iodine is an essential constituent of these hormones. Inadequate levels of iodine during gestation, especially in the first trimester, can have a potentially severe effects on the outcome of pregnancy, including stillbirth, preterm delivery, prenatal deaths, infant mortality, structural or functional anomalies, and impaired growth.
One of the greatest concerns regarding iodine deficiency during pregnancy is its impact on fetal brain development. The incidence of mentally impaired babies due to iodine deficiency is as high as 18 million.
Severe iodine deficiency during pregnancy leads to congenital hypothyroidism – a condition in which a deficiency of thyroid hormones is present at birth. It further leads to congenital iodine deficiency syndrome, also known as cretinism. The syndrome is characterized by mental deficiency and/or defects in speech, hearing, stance, and gait, and stunted growth. Various efforts in improving the iodine status of the global population have significantly reduced the incidence of severe iodine deficiency.
Nevertheless, even a moderate deficiency can cause sub-optimal cognitive function leading to reduced intellectual ability, as well as poor school performance and impaired work capacity. Mild deficiency can cause hypothyroidism in the mother, but its effects on the fetal brain remain unclear.
Iodine deficiency and Autism Spectrum Disorders (ASD)
Some studies suggest a link between iodine deficiency and autism spectrum disorder (ASD). Children with ASD had a 45% less iodine content in their hair as compared to healthy children, according to a US-based study. Another study revealed that more than half of the children with ASD had an iodine deficiency. There have been limitations to all such studies, and the scientific community needs more investigation to create a formal link between the two. No conclusions can be devised from the current scientific data.
Iodine deficiency during lactation
Neurodevelopment under the influence of thyroid hormone has three stages.The first two stages occur during fetal life, and the third stage occurs after birth. Therefore, an infant’s demand for iodine remains high even after birth - 110 micrograms in the first six months and 130 micrograms from 7-12 months. This increased demand translates into an increased iodine requirement during lactation, i.e., 290 micrograms as compared to 220 and 150 micrograms required during pregnancy and other days, respectively.Related article: an overview of lactation supplements ≫
As a child remains solely dependent on mother’s milk – at least for the first 6 months – mothers need to make sure that they are getting sufficient iodine.
Iodine deficiency and IQ
Iodine deficiency is the single most common cause of preventable intellectual disabilities in the world. It is associated with a loss of 10-15 IQ points globally. When the connection between mother’s iodine status during pregnancy and child’s IQ at the age of 8 were compared in a 2017 study, it was noticed that children of mothers with iodine to creatinine ratio below 150μg/g had comparatively poor verbal IQ, reading accuracy, and reading comprehension than the children of mothers with sufficient iodine.
Moreover, communities with sufficient iodine intake had an average 13 points higher IQ as compared to iodine-deficient communities.
Recommended intake of iodine
Iodine intake requirements are age-dependent and also change with physiological conditions like pregnancy and lactation. Average daily needs are shown in the bar chart below.
Sources of iodine
The WHO recommended dietary allowance of iodine can be fulfilled by eating a variety of iodine-containing foods. Here’s a list of foods that contain considerable amounts of iodine:
- Seafood, such as cod, tuna, shellfish, and shrimps
- Seaweed, including dulce, kelp, and nori
- Dairy products, including milk, cheese, and yogurt
- Bread and cereals
- Soy milk
- Soy sauce
Nevertheless, the use of iodized salt and other iodine fortified foods, such as bread remain the best strategy to prevent iodine deficiency because most foods have low iodine content. Note that the recommendation on the use of iodized salt is not an indication for more salt consumption. Rather it requires replacement of refined salt with iodized variety.
Iodine deficiency prevention and treatment
Iodine deficiency is prevented and treated through sufficient iodine intake in the form of iodized salt, iodine-rich diet, and iodine supplements. Hypothyroidism resulting from iodine deficiency is treated separately through medicines.
Other than the dietary sources, iodine-containing supplements are also available in the market. Women in any one of the following categories can benefit from these supplements and are recommended to take 150 μg iodine per day in supplement form:
- Women who are planning pregnancy
- Women who are pregnant
- Women who breastfeed their child
If you are pregnant or planning to embark on this beautiful journey, consult your obstetrician, GP, or healthcare provider for the use of iodine supplements.
Health risks from taking too much iodine
Excess of anything is bad. Consuming more than the recommended daily allowance of iodine can also impact thyroid health. Excess iodine can cause hyperthyroidism and autoimmune thyroid disorders.
We prefer to source information from high-quality, academically rigorous sources. These are the references we used to develop this article:
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