CLINICALLY PROVEN;

• Required for thyroid hormone T4 & T3 production and function

• Indicated with under-active thyroid

• Can be taken with Thyroxine for improved outcomes

• Supports physiological processes such as growth, metabolism and reproductive function

• Supports metabolic rate

• Involved in neuronal and cognitive development

• Protection from radiation exposure

• Supports Healthy pregnancy

• Aids foetal neurodevelopment 

• Reduces the risk of congenital abnormalities

• Reduces the risk of miscarriage and SIDS

• Prevents childhood intellectual deficits

• Improves cognitive performance in children

IODINE FUNCTION

Iodine is an essential nutrient that is required for the production of the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which are important for normal growth and development, particularly for the brain.[1] Iodine should be the first choice for health care practitioners who are looking to personalise dosing for pregnant and breastfeeding women, patients with an underactive thyroid and cognitive performance in children, or to support a general iodine deficiency. 

IODINE DEFICIENCY 

According to the World Health Organisation (WHO), a population is considered iodine deficient if the median urinary iodine concentration (UIC) is less than 100 µg/L. Several studies have demonstrated iodine deficiency is common in Australian and New Zealand women, including in areas where iodine fortification into the food supply has been introduced.[4],[5],[6],[7],[8],[9]. Results of the 2011-12 National Health Measures Survey (NHMS) concluded that 12.8% of Australians had a UIC less than 50 μg/L,[11], with a daily recommended intake of 294mcg

Iodine deficiency is common in Australian and New Zealand women.

Particular population subgroups may be more susceptible to the development of dietary iodine deficiency and require additional nutritional support. This includes women with increased iodine demands during pregnancy and lactation, and those who follow vegetarian or vegan diets that may exclude particular food groups that are naturally rich in iodine.[12],[13],[14]

High consumption of goitrogens can induce an iodine deficiency also by interfering with iodine uptake and utilisation. Iodine deficiency can also occur from iodine loss through the faeces (20%) and additional losses can occur through sweat, which although a minor eliminatory pathway under normal circumstances, can be a significant contributor for people living in hot climates (i.e. Australia) with low dietary consumption.[15]

THYROID HORMONE PRODUCTION AND FUNCTION

The function of the thyroid gland is regulated by a negative feedback loop, which involves the hypothalamus, pituitary and thyroid gland.[22],[23] The hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to secrete thyroid-stimulating hormone (TSH).[24] 

This process signals the thyroid gland to trap iodine and utilise it to produce the thyroid hormones T3 and T4, which help to regulate physiological processes such as growth, development, metabolism and reproductive function.[25],[26] 

Thyroid hormone synthesis is essential to aid the production of energy and oxygen consumption in cells, to help maintain the body's metabolic rate.[27],[28]

In target tissues, such as the liver and the brain, T3, the physiologically active thyroid hormone, can bind to thyroid receptors in the nuclei of cells and regulate gene expression. T4, the most abundant circulating thyroid hormone, can be converted to T3 by enzymes known as deiodinases in target tissues. In this manner, thyroid hormones regulate a number of physiological processes, including growth, development, metabolism and reproductive function. The presence of adequate circulating T4 decreases the sensitivity of the pituitary gland to TRH, limiting its secretion of TSH.

AIDS FOETAL NEURODEVELOPMENT 

Iodine supports women during pregnancy and lactation when the demand for iodine is increased since the foetus is reliant on the maternal free T4 (ft4) supply to produce T3, which stimulates neuronal migration and myelination. This is essential for healthy brain and central nervous system development in utero, and in infants and toddlers who are solely breastfed.[31],[32],[33],[34]

Iodine supports women during pregnancy and lactation when the demand for iodine is increased

Foetal neurodevelopment includes dendritic branching, synaptogenesis, and glial cell differentiation and migration. Importantly, it relies on an adequate supply of maternal ft4, which initiates neuronal proliferation, and the onset of neuronal migration in the cerebral cortex, hippocampus and medial ganglionic eminence. 

These developmental changes occur in the first and second trimester of pregnancy, and neuronal development continues to mature throughout the third trimester of pregnancy and during infancy.[35],

After birth, the infant relies on breast milk or formula consumption to sustain adequate dietary iodine concentrations to solely maintain adequate T4 concentrations.[39],[40]

UNDERACTIVE THYROID

Iodine is a trace element primarily required for maintaining thyroid function as it is combined with tyrosine to create thyroid hormone. There is emerging evidence that iodine plays a role outside of the thyroid, such as a potent antioxidant, promoting breast health, modulating the immune system and providing antimicrobial defence.[41]

Taking iodine orally can improve thyroid nodules. 

Iodine can be taken in combination with thyroxine, and this combination seems to work better than taking thyroxine alone. 

Taking iodized salt 200 mcg daily, in addition to thyroxine (1.5 mcg per kg daily) after surgery for benign nodular thyroid disease, seems to reduce the size of the thyroid remnant by 39.7% compared with a 10.2% reduction in patients given thyroxine alone.[42]

Also, taking iodine as potassium iodide 150 mcg/day in combination with thyroxine 50-100 mcg/day based on needs for 12 months appears to reduce nodule volume by 17.3% vs. 7.3% in the group using thyroxine alone.[43]

PREGNANCY / LACTATION SUPPORT

The pregnant woman needs more iodine for multiple reasons. The condition of pregnancy increases maternal metabolism, which requires more thyroid hormone production to sustain function. 

In addition, she must provide adequate iodine for the foetal thyroid as well as her own.[44]During pregnancy there is an increase in renal iodide clearance.[45] Severe iodine deficiency during pregnancy can result in major effects on the foetus, including congenital abnormalities and cretinism.[46]

A review paper discussed six randomised controlled trials that provided iodine supplementation at a dosage range of 50 to 230 μg/day to pregnant women with mild-moderate iodine deficiency. Low intakes of iodine during pregnancy cause maternal and foetal thyroid stress, characterized by increased thyroid size and thyroglobulin (Tg) release in both mother and newborn. 

Overall these trials found that supplementation is generally effective in minimising increases in thyroid volume during pregnancy.[47]

A clinical trial was conducted in 54 pregnant women with mild to moderate iodine deficiency (median UIC 50 μg/L) who received iodine 200 μg/day of an iodine solution or a placebo from weeks 17-18 of pregnancy until 12 months after delivery. In the control group, serum TSH, serum Tg, and thyroid size showed significant increases during pregnancy. However, those administered iodine showed no changes in TSH, thyroglobulin (TG) or thyroid size and their UIC increased to 105 μg/L.[48] Although the UIC did not achieve the WHO recommended level,[49]this amount of iodine appeared to prevent the decline in thyroid function during pregnancy.[50]

FOETAL / INFLANT / EARLY CHILDHOOD NEURONAL DEVELOPEMENT

In addition to preventing adverse outcomes in the mother, it is well known that adequate iodine levels during pregnancy and lactation are necessary for the health of the child. 

An extreme example of this is cretinism, however suboptimal iodine has also been linked to mild/moderate infant hypothyroidism and poor thyroid health at birth.[51] 

A 2006 Australian observational study found that pregnant women with a UIC<50 μg/L had a 260% increased risk of delivering a baby with a TSH>5 mI U/l; indicating hypothyroidism.[52] Furthermore, six randomised controlled studies on iodine supplementation during pregnancy found that iodine provided protection to the infant’s thyroid gland.[53] These results suggest that adequate iodine levels during pregnancy are required for infant thyroid health.

Severe iodine deficiency can produce a multitude of adverse effects on infant growth and development, collectively known as iodine-deficiency disorders (IDD). This includes permanent mental retardation such as cretinism in the offspring. 

In addition, severe iodine deficiency can cause a range of reproductive and pregnancy disorders such as hypothyroidism, decreased fertility, miscarriage and increased infant mortality.[54] Less severe states of iodine deficiency may produce mild maternal hypothyroidism or asymptomatic hypothyroxinaemia, which may result in intellectual deficits and/or neuropsychomotor deficits in the child.[55]

Adequate iodine and healthy functioning of both the maternal and the foetal thyroid glands play a critical role in foetal neuropsycho-intellectual development, due to is role in neuronal migration and myelination, peaking in the second trimester and early neonatal period. The foetus depends solely on maternal thyroid hormones during the first trimester of pregnancy. 

To accommodate for this, increasing plasma volume, renal clearance and the increased thyroid hormone degradation secondary to hyperactivity of the uterine-placental deiodinases, healthy pregnant women exhibit a surge in T4 production, partly under the stimulation of human chorionic gonadotrophin (HCG). From week 11 of gestation, foetal thyroid hormone synthesis usually begins, still dependent on maternal provision of iodine, and at term a residual 20-40% of T4 found in cord blood is of maternal origin.[56]

COGNITIVE PERFORMANCE IN CHILDREN

Thyroid hormone is essential for proper maturation of the central nervous system and crucial for myelination. This dependence is present throughout the foetal period and in the first several years of life.[57]

The effects of maternal or childhood hypothyroidism may have significant effects on the intelligence of the child. A review on iodine deficiency discussed a case-controlled study in the US that found mothers who had subclinical hypothyroidism during pregnancy had children, who at the age of seven to nine years old, had IQ scores seven points lower than controls.[58]

In support with the relationship between maternal thyroid function and child IQ, there is direct evidence that an iodine deficiency during pregnancy can influence children’s IQ. A meta-analysis of 37 studies (total of 12 291 children) in regions of China with severe iodine deficiencies found a reduction of 12.45 IQ points when compared to iodine sufficient regions. The iodine intervention was mainly iodised salt (three communities were given iodised oil). 

When pregnant mothers in severe iodine deficient regions received iodine, the children’s IQ raised 8.7 points. Further, children born 3.5 years after iodine supplementation to severe iodine deficient women, increased their IQ by 12 points.[59] These results support the use of iodine before and during pregnancy to promote intelligence in the child.

In addition to a severe iodine deficiency in pregnant women contributing to a significant lowering of childhood IQ, there is research suggesting that a mild/moderate iodine deficiency during pregnancy can cause cognitive impairment in the child. 

A prospective study carried out over a period of almost 10 years in Sicily investigated the incidence of ADHD in children born to 27 mothers in two regions with different UIC during early pregnancy: Area A – moderate iodine-deficient (median 48 μg/L); and Area B – marginally iodine sufficient (median 95 μg/L). By age ten, 11 of 16 children born to women who had a moderate iodine deficiency during pregnancy were diagnosed with ADHD compared to none in the marginally iodine deficient group. 

The authors suggest that an early gestational iodine deficiency may cause maternal hypothyroidism, which may critically reduce the amount of thyroid hormones available to the developing foetal brain.[60]As the foetal brain is solely reliant on maternal thyroid hormones before 20 weeks of gestation, these results highlight the importance of sufficient iodine intake during early pregnancy.

While the studies previously mentioned suggest that maternal iodine supplementation benefits a child’s IQ and may help to prevent ADHD, there is also research that supports supplementing children directly with iodine for IQ. A randomised, placebo-controlled, double-blind trial was conducted in 184 mildly iodine deficient children aged 10–13 years in New Zealand. 

Children were randomly assigned to receive a daily tablet containing either iodine 150 µg or placebo for 28 weeks. After 28 weeks, iodine status improved in the supplemented group (UIC: 145 lg/L; thyroglobulin: 8.5 lg/L), whereas the placebo group remained iodine deficient (UIC: 81 lg/L; thyroglobulin: 11.6 lg/L). Iodine supplementation significantly improved scores for two of the four cognitive subtests [picture concepts (P = 0.023) and matrix reasoning (P = 0.040)] but not for letter-number sequencing (P = 0.480) or symbol search (P = 0.608) (Table 3). 

The overall cognitive score of the iodine supplemented group was 0.19 standard deviations (SDs) higher than that of the placebo group (P = 0.011). The authors concluded that iodine supplementation improved perceptual reasoning in mildly iodine-deficient children and suggests that mild iodine deficiency could prevent children from attaining their full intellectual potential.[61]

RADIATION EXPOSURE

Radiation emergencies can vary in scale, from isolated occupational or medical overexposure of radiation to an individual, to far reaching catastrophes with potential global effects.[63] Taking potassium iodide is effective for preventing thyroid uptake of radioactive iodine. However, potassium iodide works only to prevent the uptake of radioactive iodine into the thyroid gland. It is not a general radio-protective agent,[64] nor is it effective as a prophylaxis in case of a radiation emergency.[65] Doses of potassium iodide protect for about 24 hours. 

Therefore, it should be taken daily until the risk of radiation exposure no longer exists. See table 4 below for the Food and Drug Administration’s 2001 recommendation for administration of potassium for radiation emergencies.[66]