Iodine and Your Hormones: The Missing Link in Thyroid and Endocrine Health (and When NOT to Supplement)
Years ago, when I was first learning about Hashimoto’s and hypothyroidism, I came across research on iodine and its importance to thyroid function. I immediately began wondering if it was something I should be supplementing with - was it going to be one of the keys to my recovery?
Then I came across other research suggesting that too much iodine could be just as problematic as too little. What?! I was more than a little confused, and I don’t think I was alone in this.
What I’ve realised since then is that iodine is incredibly powerful if used correctly, but its safety and efficacy are contextual.
It’s not as simple as “deficient? take more” — in fact, that approach can backfire badly. Your thyroid doesn’t operate in isolation. It’s part of a complex endocrine network involving your adrenal glands, ovaries or testes, liver, and even your gut. Iodine interacts with all of these systems, and whether it helps or harms depends on the state of the whole network.
For some people, adding iodine without first addressing nutrient gaps, inflammation, or adrenal dysregulation can trigger symptoms ranging from palpitations and anxiety to an autoimmune flare. For others, the right amount, in the right form, can be transformative — improving energy, metabolism, and hormonal balance.
In this article, we’ll unpack iodine’s many roles in the thyroid and beyond, look at how it connects to conditions like PCOS, endometriosis, adrenal fatigue, and even breast cancer, and explore why more isn’t always better. Most importantly, I’ll walk you through what needs to be in place before you even consider supplementation, and how to use it safely and synergistically if it’s right for you.
What Iodine Actually Does in the Body
Iodine’s most well-known role is as a key building block for thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These hormones are critical for regulating metabolism, growth, and energy production in virtually every cell. But iodine doesn’t just stop at thyroid hormone production.
It’s also concentrated in the breasts, ovaries, prostate, and salivary glands, where it supports tissue health, modulates oestrogen activity, and even acts as an antioxidant. In the immune system, iodine can influence the balance between pro- and anti-inflammatory processes, which is part of the reason it’s implicated in autoimmune thyroid disease.
On a cellular level, iodine appears to protect against abnormal cell growth, which is why research has explored its relationship with certain cancers, including breast and prostate cancer. In reproductive health, iodine helps maintain normal ovarian function and may influence progesterone and testosterone balance.
Given this wide-ranging influence, it’s easy to see why both deficiency and excess can cause problems — and why “safe” levels are so dependent on your personal physiology, nutrient status, and underlying conditions.
Why Iodine Isn’t Just a “Thyroid Nutrient”
The notion that iodine is only involved in thyroid health is misguided. Its functions are far more diverse. In women, iodine is found in high concentrations in the breasts, ovaries, and cervix, where it plays a role in regulating tissue growth, supporting lactation, and modulating oestrogen metabolism. In men, the prostate also accumulates iodine, where it may have anti-proliferative effects.
It’s also utilised by the immune system, and it functions as a natural antioxidant in specific tissues. This is why research links iodine deficiency not only to goitre and hypothyroidism but also to reproductive challenges, fibrocystic breast changes, and certain cancers.
Conditions Where Iodine May Play a Role
1. Hypothyroidism & Hashimoto’s
The thyroid gland requires iodine to synthesise T4 and T3. But in autoimmune thyroiditis, finding the right balance and timing of supplementation is key - excessive iodine without adequate selenium can increase oxidative stress and accelerate gland damage.
2. Hyperthyroidism
Iodine availability can impact thyroid hormone output. In certain hyperthyroid states, such as Graves’ disease or toxic multinodular goitre, excess iodine can trigger increased hormone production
3. PCOS (Polycystic Ovary Syndrome)
Iodine is concentrated in the ovaries, where it contributes to normal follicular development and oestrogen regulation. Emerging research suggests a possible relationship between iodine status, ovarian function, and menstrual regularity.
4. Endometriosis
Iodine may help modulate oestrogen activity and oxidative stress in reproductive tissues, with preliminary evidence indicating a potential protective role in abnormal cell proliferation.
5. Adrenal Fatigue / HPA Axis Dysregulation
While iodine is not directly stored in the adrenal glands, thyroid function and adrenal activity are interconnected. Adequate iodine status supports metabolic processes influenced by thyroid-adrenal interactions.
6. Fatty Liver
The liver plays a key role in converting T4 to active T3. Iodine availability affects thyroid hormone synthesis, which in turn impacts hepatic metabolism and lipid regulation. Low iodine status can contribute to non-alcoholic fatty liver disease.
7. Breast Cancer
Research indicates that molecular iodine may have anti-proliferative and pro-apoptotic effects in breast tissue, potentially linked to antioxidant activity and modulation of hormone signalling.
The key message here?
Iodine deficiency is dangerous to far more than just your thyroid.
Why Iodine Supplementation Isn’t Always Appropriate
In saying that, just because a test shows low iodine doesn’t mean you should start supplementing. Here’s why:
The Selenium Connection – Without adequate selenium, iodine can drive thyroid inflammation. Why? Adequate selenium status is essential before supplementing with iodine because selenium is a critical component of the enzymes called iodothyronine deiodinases, which convert T4 into its active form T3, and glutathione peroxidases, which protect the thyroid gland from oxidative damage caused by iodine metabolism. Insufficient selenium impairs these processes, increasing the risk of thyroid dysfunction and oxidative stress when iodine intake is increased, potentially exacerbating hypothyroidism or autoimmune thyroid conditions. ALWAYS check your selenium status before adding iodine.
Adrenal Stability – When cortisol levels are unstable—whether chronically elevated, insufficient, or fluctuating—supplementing with iodine can inadvertently overstimulate the metabolic system, potentially exacerbating symptoms such as fatigue and anxiety. This is because cortisol plays an important regulatory role in thyroid hormone activity and overall metabolic balance. If cortisol is dysregulated, the body’s response to increased thyroid hormone production may become unpredictable, leading to an overactivation of metabolism that the system can’t cope with. This overstimulation can increase energy demands and sympathetic nervous system activity, triggering heightened anxiety and worsening feelings of exhaustion rather than improving them. Stabilising cortisol and adrenal function before increasing iodine intake is crucial to avoid aggravating these symptoms and to support a balanced metabolic response.
Gut Health – Dysbiosis, an imbalance in the gut microbial community, along with low stomach acid (hypochlorhydria), can significantly impair iodine absorption in the digestive tract, reducing the effectiveness of iodine supplementation. Adequate stomach acid is essential for the proper breakdown of food and the release of minerals, including iodine, making them available for absorption in the intestines. When stomach acid is insufficient, iodine may remain bound within food matrices or be altered by pathogenic bacteria proliferating due to dysbiosis, limiting its bioavailability. Dysbiosis can also disrupt the integrity of the gut lining and the balance of beneficial bacteria that assist in nutrient metabolism and absorption, further hindering iodine uptake. This means supporting gut health before supplementation is crucial - otherwise, you’re probably just going to be wasting your time and money.
Autoimmune Status – During active autoimmune flares, iodine supplementation can exacerbate the inflammatory response by effectively acting like fuel on the fire. This occurs because iodine influences thyroid hormone production, which can increase immune system activity and oxidative stress within the thyroid and other tissues. In the context of an autoimmune flare, where the immune system is already hyperactive and attacking the body’s cells, additional iodine may intensify this immune activation, worsening inflammation and potentially aggravating symptoms such as pain, fatigue, and tissue damage. This is likely related to other nutrient deficiencies that need to be addressed before introducing iodine.
All of these issues mean it’s key to bring iodine in at the right time. Too soon, and you’ll end up creating more problems than you’re solving.
Steps Before Considering Iodine Supplementation
Test First – Urinary iodine loading tests or 24-hour iodine excretion tests give a clearer picture of your iodine status than blood tests alone because most iodine leaves the body through urine. Blood tests show iodine in circulation, but don’t always reflect how much your body is actually using or getting rid of. Checking iodine this way helps spot if you’re low or high and makes it easier to tailor supplementation.
Support Antioxidant Defences – Before starting iodine supplements, it’s a good idea to make sure you’re getting enough selenium, zinc, vitamin A, and vitamin C. These nutrients help your thyroid work properly and protect your body from the extra stress iodine can sometimes cause. Selenium helps activate thyroid hormones and keeps inflammation in check, zinc supports your immune system and hormone production, and vitamins A and C act as antioxidants to keep things balanced. Having these nutrients in place makes iodine supplementation safer and more effective.
Balance the Adrenals – To keep your cortisol levels steady, it’s important to manage stress through techniques like mindfulness or gentle movement, balance your blood sugar with regular, nourishing meals (including plenty of protein!), and prioritise getting enough good-quality sleep. You can also supplement to address adrenal dysfunction. When these areas are in check, your body can better handle changes in metabolism and energy demands. This stability helps prevent issues like anxiety or fatigue that can come from cortisol swings.
Address Gut & Liver Function – To help your body absorb iodine properly, it’s key to optimise bile flow, keep your stomach acid levels healthy, and support a diverse gut microbiome. Good bile flow aids fat digestion, stomach acid breaks down food and releases minerals, and a balanced microbiome helps with nutrient absorption. Together, these make sure your digestion runs smoothly and your iodine supplements actually work.
Titrate Slowly – It’s best to start with a low dose of iodine, such as from dietary sources like seaweed, and keep an eye on how you’re feeling. This approach helps you avoid overstimulating your thyroid or metabolism too quickly. Monitoring symptoms lets you adjust safely and find the right balance for your body.
The Bottom Line
Iodine is one of the most misunderstood nutrients in endocrine health. It’s neither a magic bullet nor a villain — its impact depends entirely on context. With the right preparation, personalised dosing, and synergistic nutrients, iodine can support not just your thyroid, but your whole hormonal ecosystem. But jump in too soon, and you risk doing more harm than good.
If you’re thinking about iodine supplementation, book a discovery call with me by clicking here to get personalised guidance on testing, preparing, and safely introducing it by taking into account your thyroid, adrenal, and liver health.
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