Side Effects of Excessive Intake of Iodine Supplements

Iodine is a trace element that is essential for the production of thyroid hormones. Iodine supplementation is suggested for individuals affected by its deficiency. However, adverse effects can be experienced due to an overdose. This HealthHearty write-up provides information on the side effects of an overdose of iodine supplements.

Did You Know?

Although the daily tolerable upper intake level for iodine is 1,100 mcg, a study published in the American Journal of Clinical Nutrition revealed the onset of subclinical hypothyroidism in subjects who were taking relatively higher doses of 400 mcg or more on a daily basis. Though individuals affected by this condition usually doesn’t show symptoms of hypothyroidism, there’s a possibility that this condition could progress into hypothyroidism.

Goiter is a medical condition that is characterized by abnormal enlargement of the thyroid gland. It occurs when the thyroid gland is unable to produce sufficient amounts of thyroid hormones, which in turn could occur if the body’s requirement for iodine is not met due to a poor diet. In some cases, the presence of nodules in the gland could cause excessive production of thyroid hormones, thereby leading to goiter. There are certain food items that contain goitrogenic compounds, which interfere with thyroid peroxidase (an enzyme that is responsible for adding iodine during the production of thyroid hormones). It is believed that excessive consumption of goitrogenic compounds such as soy isoflavones and isothiocyanates present in cruciferous vegetables could be a contributing factor for an iodine deficiency. In the United States and other developed countries, the addition of iodine to table salt has helped in countering the issue of iodine deficiency to a great extent.

The use of iodine supplements is usually recommended in case of individuals affected by a severe deficiency of iodine. However, the American Thyroid Association has warned against the indiscriminate use of iodine supplements, as these might contain iodine in amounts that are up to several thousand times higher than the daily tolerable upper limit.

Recommended Dietary Allowance for Iodine

The recommended dietary allowance suggested by the Institute of Medicine’s Food and Nutrition Board for different age groups is as follows:

In case of infants up to the age of one year, the table provides AI (adequate intake) values.

The following table presents the tolerable upper intake level, which is the maximum nutrient intake that does not pose a risk of adverse effects. It must be noted that it is not possible to establish the upper intake level in infants up to the age of one year.

Though the upper tolerable limit is 1,100 mcg daily, the American Thyroid Association (ATA) issued a statement warning against the potential risks of the intake of too much iodine, especially from iodine, potassium iodide, and kelp supplements. The main reason behind issuing this statement was their belief that such supplements might contain iodine in large doses. Thus, individuals who are taking these supplements for the treatment of iodine deficiency must consult their healthcare provider regarding the right dosage. It would be best to avoid taking iodine in dosages higher than 500 mcg daily. As per ATA, a daily dosage of 1,100 mcg of iodine could put such individuals at a higher risk of developing thyroid dysfunction.

Side Effects of Iodine Supplementation

It must be noted that excess iodine can also lead to high levels of TSH (thyroid-stimulating hormone). TSH is a hormone produced by the pituitary gland, which releases TSH when the levels of thyroid hormones are low. The release of TSH stimulates the secretion of T3 (triiodothyronine) and T4 (thyroxine) hormones by the thyroid gland. Triiodothyronine is essential for proper growth and development. Thyroid hormones also play a vital role in metabolism and temperature regulation. In case of iodine-deficient individuals, excess iodine intake through supplementation increases the risk of iodine-induced hyperthyroidism. It could also put one at an increased risk of developing autonomous thyroid nodules. On the other hand, excessive intake through supplements by iodine-sufficient individuals could put them at a risk of developing hypothyroidism, goiter, and high levels of TSH in the blood.

It must be noted that the dosage that might be considered safe for the general population might not apply to individuals who are affected by an iodine deficiency or autoimmune thyroid disease. Thus, caution must be exercised while prescribing iodine supplements to individuals who might have increased sensitivity to excess iodine intake. Increased intake of iodine has also be linked to the development of thyroiditis and thyroid papillary cancer.

Iodine can cause adverse effects in some individuals. The common side effects of taking too much iodine include:

✦ Nausea
✦ Abdominal pain
✦ Headache
✦ Metallic taste in the mouth
✦ Diarrhea

In case of individuals who are sensitive to iodine, higher doses could cause the following untoward effects:

✦ Swelling of the lips and face (angioedema)
✦ Sore teeth and gums
✦ Increased saliva
✦ Burning sensation in the mouth and throat
✦ Throat inflammation
✦ Skin problems
✦ Severe bleeding
✦ Bruising
✦ Fever
✦ Joint pain
✦ Enlarged lymph nodes
✦ Allergic reaction

Though taking iodine supplements in prescribed doses is not likely to cause any adverse effects, do inform your healthcare provider if you experience any untoward effects. Also, iodine can interact with antithyroid drugs, drugs for high blood pressure, lithium, etc. The intake of iodine in larger doses can put both, adults as well as children at an increased risk of developing thyroid problems.

Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.