What Is Iodine?
Iodine is a mineral required by the human body, but not made by the human body. Therefore, iodine must be supplied by the diet. Iodine is responsible for many functions, including thyroid hormone production and growth and development . Iodine plays a major role in brain and bone development, particularly during pregnancy and infancy .
Why Care About Iodine and the Thyroid?
The thyroid is an endocrine gland located on the lower, front part of the neck. Its main responsibility is to make thyroid hormones that are used by body to sustain energy, activate the brain and muscles, and keep organs working promptly. The thyroid gland uses iodine consumed from food to make the hormones. Then, the hypothalamus and pituitary gland in the brain signal to the thyroid gland to release the necessary hormones when in demand.
A thyroid blood panel is necessary for learning about an individual’s thyroid hormone production. Particular biomarkers of interest are T3, T4, and TSH.
Free trihydrothyronine (T3) is a hormone that plays a role in growth and development, metabolism, body temperature, and heart rate. “Free” means that it is the amount in circulation available to cells. Low T3 levels may indicate hypothyroidism.
Free thyroxine (T4) is the main hormone secreted into the bloodstream by the thyroid gland. It is converted into the active form (T3). Low levels of T4 may indicate hypothyroidism.
Thyroid-stimulating hormone (TSH) is a hormone that stimulates the thyroid gland to produce enzymes (T3, T4) that, in turn, stimulate tissue metabolism in the body. High levels of TSH may indicate hypothyroidism.
What Happens If You Don’t Consume Enough Iodine?
When the body is iodine deficient, hypothyroidism develops. Symptoms of hypothyroidism include fatigue, constipation, weight gain, muscle weakness, or stiffness. If left untreated, hypothyroidism can lead to other health problems such as heart disease and obesity, highlighting the impact that thyroid hormones can have on the entire body.
What Happens If You Consume Too Much Iodine?
Excess consumption of iodine leads to hyperthyroidism, where the output of thyroid hormone production is elevated and too many hormones are being distributed throughout the body. Common symptoms of hyperthyroidism include:
- Increased appetite
- Irregular heartbeat
- Difficulty sleeping
Both hypo- and hyperthyroidism require medical attention and treatment.
How Much Iodine Do You Need Per Day?
Generally healthy adults require a daily amount of 150 micrograms of iodine per day. Pregnant and lactating women have increased requirements, within the range of 220-290 micrograms per day . In general, iodine consumption is necessary to provide thyroid hormone production and prevent goiter formation . While rare, iodine deficiency can be found in populations where iodized salt is not used, geographic regions with low iodine soil content, and in pregnant women. Appropriate iodine levels are met by consuming a variety of foods, such as: 
- saltwater fish
- seaweed (including kelp)
- certain dairy products
- iodized salt and/or supplements
What Are the Signs of Low Iodine?
If deficient in iodine, goiter is the first noticeable sign. A sufficient amount of thyroid hormones may be compromised with an iodine deficiency and may be evidenced by specific biomarkers . Pregnant women with severe iodine deficiency may see stunted growth, mental retardation, and/or delayed sexual development in their babies after birth. While there is research supporting these concerns, it is important to consult with your healthcare provider before taking any supplementation at any stage of life as there are warnings associated with consumption.
What Are the Signs of High Iodine?
Alternatively, too much iodine from food and or supplementation can result in hyperthyroidism and worsen health issues . Similar to deficiency, excessive intake yields an enlarged goiter as commonly the first, visible symptom . It is highly recommended that the use of any iodine product be under the direct supervision of a healthcare provider due to possible side effects and medication interference.
Where Do You Find Iodine?
Iodine is naturally found in soil, seawater, and food. Specific foods such as fish, shellfish, seaweed, grains, fruits, vegetables, and dairy products contain iodine. Most notable, iodine is added to table salt and is indicated in the ingredient list as “iodized.” Most processed foods will contain iodized salt. However, the mineral amounts are not actually disclosed on a Nutrition Facts label.
More often than not, Americans do not need to actively seek additional iodine consumption as they typically consume the appropriate iodine levels by eating a variety of foods on a daily basis . For reference, one teaspoon of iodized salt contains 250 micrograms of iodine, surpassing the daily recommended intake. It is best to consult with a registered dietician or nutritionist if there are concerns about specific foods and their iodine amounts.