Iodine

Why iodine is good for you

Iodine is required to make the thyroid hormones that regulate metabolism. While iodine’s only function is to make thyroid hormones, it still has a very important role in the body. The thyroid hormones play a big role in growth, cell reproduction, nerve functions and how cells use oxygen. One of the thyroid hormones – thyroxin – regulates how fast energy is used from food. If there is not enough dietary iodine, the thyroid swells up in an effort to make more hormones, a condition that is called hypothyroidism (an underactive thyroid). The swelling is called goitre.

Important iodine facts

• Iodine is a trace mineral, which means only a small amount of it is required in the diet to ensure good health
• Iodine is needed to create thyroid hormones TSH, T3 and T4. These hormones regulate all cells in the body, including metabolism
• Iodine levels are tested as soon as a baby is born, to test for neurological issues
• Most of the iodine, about 75%, is stored in the thyroid
• Iodine deficiency in pregnancy causes a severe form of disability in newborns called congenital hypothyroidism, which causes impaired neurological function, stunted growth, and physical deformities
• Iodine, in the form of potassium iodide, is used in the case of nuclear reactor accidents to protect the thyroid gland from damage (including thyroid cancer) by absorbing the radioactive iodine that is released
• Until well into the 20th century, iodine deficiency was a serious problem in the western world. To solve the iodine problem, salt producers began adding iodine to table salt around 1924. Iodine deficient diseases (such as goitre) soon disappeared
• Today there are more people developing thyroid cancer and other thyroid disorders and experts believe it is due to the use of sea salt to season food, which has very little iodine in it

Iodine works best with

• Vitamin B1
• Vitamin B2
• Vitamin B3
• Vitamin B5
• Vitamin B6
• Vitamin B12
• Vitamin C
• Vitamin D
• Tyrosine
• Copper
• Magnesium
• Zinc

Iodine and health

• Radiation-induced thyroid cancer
  Iodine deficient individuals are at increased risk of developing radiation-induced thyroid cancer because they will accumulate greater amounts of radioactive iodine. Potassium iodide administered in pharmaecological doses within 48 hours before or 8 hours after radiation exposure from a nuclear reactor accident can significantly reduce thyroid uptake of and decrease the risk of radiation-induced thyroid cancer. This was noticed in Poland after the Chernobyl nuclear accident
• Preventing certain birth defects in pregnancy
  Iodine is required in pregnancy (at higher levels than normal) to ensure that the unborn child will not develop brain/mental development retardation and will grow up healthy mentally
• Fibrocystic breast disease
  This is a condition of the breasts that is benign (non-cancerous). One study showed that iodine deficiency leads to fibrocystic breast condition, while iodine supplementation was found to reverse those changes. In another study of women with fibrocystic breast condition were treated with iodine supplementation and 70% reported improvement in their symptoms. Further research needs to be undertaken in order to further validate these findings in larger studies
• Preventing thyroid goitre
  Iodine is vital for the healthy functioning of the thyroid gland and helps to prevent thyroid goitre, a non-cancerous condition in which the thyroid gland enlarges in size and which can be caused mainly due to an iodine deficiency. When the diet does not provide sufficient iodine, the thyroid swells up in an effort to make more hormones and this is how thyroid goitre develops.
• Preventing thyroid cancer
  Studies show that iodine prevents thyroid cancer, specifically radiation-induced thyroid cancer, which is caused when high levels of radioactive iodine are absorbed from any type of radioactive substances with this radioactive isotope (such as in nuclear reactor accidents). Studies also show that when potassium iodide is administered in pharmacological doses either 48 hours before or within 8 hours after radiation exposure from a nuclear reactor accident can significantly reduce thyroid uptake of and decrease the risk of radiation-induced thyroid cancer. Other recent studies show that a preference for eating rock salt instead of iodised salt has resulted in an increase in the number of thyroid cancers in some areas of Australia
• Reduces the risk of developing some types of hearing loss
  Recent research suggests that some forms of hearing loss could be due to an iodine deficiency.
• Keeps skin, hair, nails healthy
  Iodine is essential for healthy skin, hair and nails – it ensures hair is shiny and soft, skin is supple and glowing and nails are healthy and strong.

People who wish to take an iodine supplement should talk to a medical professional before taking it.

Groups at risk of iodine deficiency

Iodine deficiency is becoming more increasingly common, with more the population being at risk of iodine deficiency. The following are the groups who may be at a high risk of having an iodine deficiency:

• Pregnant and breastfeeding women
  People who are pregnant or breastfeeding, should get enough iodine in their diet because it helps to ensure that their unborn child has healthy and normal brain development. A deficiency of iodine in the mother’s diet may cause delay in brain development and other abnormalities. Women who are breastfeeding should also ensure that they have enough iodine in their diet to help their baby’s growth and brain development continues in a healthy manner
• People with goitre
  People with the health condition goitre, where the thyroid becomes enlarged and causes symptoms of hypothyroidism may not have a healthy and properly functioning thyroid. Getting some extra iodine may help the thyroid function better and reduce some of they symptoms of hypothyroidism
• Eating too many goitrogenic foods
  Certain foods are known as goitrogenic foods – cabbage, Brussels sprouts, broccoli, turnips, cassava, mustard greens, bok choy, cress, kale, kohlrabi, soy. These goitrogenic foods interfere with the proper functioning of the thyroid, by blocking iodine absorption and cause symptoms associated with iodine deficiency. Cooking these foods deactivates the iodine-blocking substance inside them. The only food that this rule does not apply is soy – nothing seems to deactivate the iodine-blocking agent within soy, so people who are iodine deficient should avoid soy

People in these groups at risk of deficiency should talk to a medical professional about iodine supplements before taking them.

Women who are pregnant should get enough iodine in their diet because it helps to ensure that their unborn child has healthy and normal brain development

Symptoms of iodine deficiency

Iodine deficiency occurs when less than 50mcg of iodine is taken in food each day.

Iodine deficiency is normally rare in western countries, but with the high usage of sea salt (which contains little iodine), it is becoming far too common today. Symptoms of iodine deficiency are usually goitre and hypothyroidism.

Symptoms of iodine deficiency are:

• Deafness, delayed brain function and growth (children)
• Goitre, hypothyroidism (adults)
• Benign fibrocystic breast disease (women)

People who experience any of the symptoms above should seek the advice of their doctor about iodine

Iodine in food

Iodine recommended daily intake (RDI)

The tolerable upper limits should only be taken for short periods and only under medical supervision.

* The tolerable upper limit for iodine for infants aged 0-12 months has not yet been determined due to a lack of data about the adverse effects in this age group. The only source of iodine intake should be from food (breast milk and/or baby formula).

Toxic Levels of Iodine

Iodine is toxic at doses greater than 2000mcg (2mg) per day.

Acute iodine toxicity 

Acute toxicity from taking too much in iron supplements – even over 100mg can cause the following symptoms:

• Extreme tiredness or weakness
• Fever
• Numbness and tingling in hands or feet
• Severe abdominal pain and irritation
• Skin rash
• Swelling of salivary glands *
• Swollen heart *

* People who experience the highlighted symptoms should seek immediate emergency treatment.

Chronic iodine toxicity 

Chronic toxicity of iodine from taking higher than the therapeutic dose of iodine supplements for a long time can cause the following symptoms:

• Abdominal pain
• Brassy or metallic taste in the mouth
• Burning sensation in the mouth or throat
• Decreased thyroid activity
• Diarrhoea
• Fatigue
• Goitre (ironically this condition can develop from too little iodine too)
• Grave’s disease
• Headache
• Head cold symptoms
• Hyperthyroidism
• Increased salivation
• Skin rash
• Sore teeth and gums
• Stomach irritation

People who experience any of the above toxicity symptoms should discontinue their iodine supplements and see their doctor for advice.

Overdosage and toxicity is more likely to occur from taking too many supplements, whereas dietary intake of iodine is highly unlikely to cause overdosage.

Precautions

People taking lithium carbonate for manic depressive illness should NOT take iodine as it suppresses the thyroid gland and can produce abnormally low thyroid activity.

Be careful when taking extra iodine supplements as excessive amounts can cause hyperthyroidism, a condition where the thyroid overreacts and this can cause another set of problems.

Iodine interactions with medications and supplements

The following are the medications that are more likely to cause a reaction with iodine supplements:

• Lithium carbonate
  People taking the medication lithium carbonate for bipolar disorder (manic-depressive illness) should avoid taking iodine supplements, as the lithium carbonate suppresses the thyroid gland’s function and causes the thyroid activity to be abnormally low.

People taking the medication lithium carbonate for bipolar disorder (manic-depressive illness) should avoid taking iodine supplements

Other interactions with iodine

There are none reported.

Iodine’s effect on lab tests

Iodine has the following effect on lab tests:

• Steroid hormones in urine
  Iodine supplementation can interfere with and produce incorrect results for steroid hormone in urine.
• Thyroid function studies
  Iodine supplementation can also cause false elevation of all hormones in thyroid function studies and produce incorrect results.

References

• USDA National Nutrient Database – provides nutrient values for foods (accessed 5 January 2005)
• Osiecki, H. The Nutrient Bible. Bio-Concepts Publishing QLD, 2002
• Whitney EN, Cataldo DB, Rolfes SR. Understanding Normal and Clinical Nutrition, 6th Edition. Wadsworth/Thomson Learning, 2002

Last updated: 6 May 2024