Key Takeaways
- Iodine is essential for the production of thyroid hormones.
- Both too little and too much iodine can negatively affect thyroid function.
- Excessive iodine intake may worsen autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease.
- Gut health plays an important role in iodine absorption and thyroid health.
- A dietary assessment is often more useful than a single urinary iodine test when evaluating long-term iodine intake.
If you have Hashimoto’s thyroiditis, Graves’ disease, or another thyroid condition, understanding your individual iodine requirements is essential. While iodine is often promoted as a thyroid-supporting nutrient, more is not always better.
What Is Iodine and Why Is It Important?
Iodine is an essential mineral required for the production of thyroid hormones. The thyroid gland uses iodine to produce triiodothyronine (T3) and thyroxine (T4), hormones that are involved in pretty much all body processes including regulating metabolism, energy production, mood and memory and brain function.
Beyond the thyroid, iodine also plays important roles throughout the body. Research suggests iodine contributes to:
- Healthy stomach acid production
- Breast tissue health – reducing breast cancer risk and fibrocystic breasts
- Reproductive health including fertility
How Is Iodine Absorbed?
Approximately 90% of dietary iodine is absorbed in the duodenum, the first section of the small intestine.
This means that digestive conditions associated with intestinal inflammation may impair iodine absorption, including:
- Coeliac disease
- Small intestinal bacterial overgrowth (SIBO)
- Inflammatory bowel conditions such as Crohns Disease and Ulcerative Colitis
Once absorbed, iodine enters the bloodstream and is transported into the thyroid gland via a specialised protein known as the sodium-iodide symporter.
Inside the thyroid cells (thyrocytes), iodine is incorporated into the thyroid hormones T3 and T4. These hormones are then released into the bloodstream under the regulation of thyroid stimulating hormone (TSH).
Can Too Much Iodine Be Harmful?
When it comes to thyroid health, iodine intake is all about balance.
While iodine deficiency can impair thyroid hormone production, excessive iodine intake may worsen autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease.
Research suggests that excessive iodine intake may:
- Increase thyroid antibody levels
- Trigger immune dysregulation
- Contribute to thyroid inflammation
- Worsen symptoms in susceptible individuals
One proposed mechanism involves the gut microbiome. Due to its antimicrobial properties, excessive iodine may reduce beneficial butyrate-producing bacteria. These bacteria help regulate inflammation and support immune function. A reduction in these microbes may contribute to increased intestinal permeability, systemic inflammation, and autoimmune activity.
For most adults, the Recommended Dietary Intake (RDI) for iodine in Australia is 150 micrograms per day. Obtaining iodine primarily through whole food sources rather than high-dose supplementation is often the safest approach.
Iodine and Graves’ Disease: Should You Avoid It?
Many people with Graves’ disease are told to avoid iodine completely. However, current evidence suggests the relationship is more nuanced.
A recent systematic review found that individuals with Graves’ disease who consumed adequate amounts of iodine experienced higher remission rates and lower recurrence rates compared with those consuming insufficient or excessive amounts.
This highlights an important principle: optimal thyroid health requires adequate iodine intake—not deficiency, but not excess either.
The goal is to find the right amount for your individual needs.
Is Urinary Iodine Testing Accurate?
Urinary iodine testing is commonly used to assess recent iodine intake because approximately 90% of consumed iodine is excreted through the kidneys within 24 hours.
While urinary iodine can be useful at a population level, it has limitations when assessing an individual’s long-term iodine status.
Daily iodine intake can vary significantly depending on food choices. For example, someone may consume iodine-rich foods such as seaweed or sushi one day and very little iodine over the following several days.
For this reason, a single spot urine test may not accurately reflect long-term iodine intake.
In clinical practice, a comprehensive dietary assessment often provides a more meaningful picture of an individual’s iodine status and overall thyroid health.
When Should You Assess Your Iodine Intake?
Assessing iodine intake may be beneficial if you have:
- Hashimoto’s thyroiditis
- Graves’ disease
- Hypothyroidism
- Hyperthyroidism
- A history of restrictive diets
- Digestive disorders affecting nutrient absorption
- Symptoms of thyroid dysfunction
A personalised assessment can help determine whether your iodine intake is appropriate for your individual health needs.
Frequently Asked Questions
Can iodine improve thyroid function?
Iodine is essential for thyroid hormone production, but more iodine does not necessarily improve thyroid function. Both deficiency and excess can negatively affect thyroid health.
Should people with Hashimoto’s and Graves Disease avoid iodine?
Not necessarily. People with Hashimoto’s and Graves Disease generally benefit from adequate iodine intake rather than excessive supplementation. Individual requirements vary and should be assessed on a case-by-case basis.
Is seaweed a good source of iodine?
Seaweed can be an excellent source of iodine, but some varieties contain very high amounts. Regular consumption of large quantities may contribute to excessive iodine intake.
Can gut health affect iodine absorption?
Yes. Because iodine is primarily absorbed in the small intestine, conditions affecting gut health may influence iodine absorption and thyroid function.
Seeking Personalised Thyroid Support?
If you’re feeling confused about iodine, Hashimoto’s thyroiditis, Graves’ disease, or thyroid nutrition, a personalised assessment can help clarify your individual requirements.
As a naturopath and nutritionist supporting clients across Sydney, Melbourne and Australia-wide via telehealth, I provide evidence-informed guidance on thyroid health, gut health, hormone balance and nutritional medicine.
Book an appointment today to understand your iodine needs and develop a personalised plan to support your thyroid health.
