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Written by: Lauren Chamberlain

Edited and Reviewed By: Anabelle Clebaner MS, RDN

Iodine is a powerhouse nutrient that plays a vital role in thyroid function, hormone balance, and reproductive health. Despite its importance, many people—especially women—don’t get enough of it, leading to potential health complications. Beyond its well-known effects on thyroid function, recent research suggests that iodine plays a role in glucose metabolism, insulin sensitivity, and fertility. In this post, we’ll explore iodine’s impact on the body, its connection to thyroid and reproductive health, and why you should consider testing your iodine levels!

Iodine and the Thyroid: A Critical Connection

The thyroid gland depends on iodine to produce hormones that regulate metabolism, energy levels, and overall endocrine balance. Here’s how it works:

Thyroxine (T4): Contains four iodine molecules and serves as a storage form of thyroid hormone.
Triiodothyronine (T3): Contains three iodine molecules and is the active thyroid hormone that influences metabolism and energy levels.

When you consume iodine, it gets absorbed in the gastrointestinal tract and transported to the thyroid via the sodium-iodide symporter (NIS). If your body detects low thyroid hormone levels, the pituitary gland releases thyroid-stimulating hormone (TSH) to prompt the thyroid to absorb iodine and produce more T4, which then converts into the active T3.

Why Does TSH Increase with Iodine Supplementation?

A rise in TSH after starting iodine supplements is often misunderstood. TSH stimulates more NIS molecules, helping transport iodine into thyroid cells. A temporary increase in TSH is a normal response, not necessarily a sign of thyroid dysfunction. However, excessive iodine intake can paradoxically impair thyroid function by triggering hypothyroidism or autoimmune thyroiditis. This is why careful monitoring through the use of a health professional is essential.

Iodine’s Role in Women’s Health

Beyond the thyroid, iodine plays a crucial role in reproductive health, hormone balance, and even breast tissue integrity. Here’s how:

Ovulation & Progesterone Production

Iodine is essential for ovarian function because the ovaries store a lot of iodine because our growing follicles take up iodine to grow properly. Studies suggest that iodine deficiency may contribute to menstrual irregularities and impaired ovulation, potentially affecting fertility.

Endometriosis & Estrogen Dominance

Iodine helps regulate estrogen metabolism by promoting the breakdown of estrogen into more favorable metabolites. This may help reduce inflammation, fibrocystic breast changes, and the risk of estrogen-dominant conditions like endometriosis.

Breast & Uterine Health

Iodine accumulates in breast and uterine tissues, where it supports cellular integrity and may protect against fibrocystic breast disease. A deficiency in iodine has been linked to an increased risk of breast cancer due to impaired estrogen metabolism and oxidative stress.

Pregnancy & Fetal Development

Iodine is crucial during pregnancy, as it supports fetal brain development, prevents cretinism, and reduces the risk of miscarriage and low birth weight. A deficiency in pregnancy can lead to intellectual disabilities, developmental delays, and even maternal hypothyroidism, which can have long-term effects on the child.

Iodine Absorption & Halogens: A Competitive Battle

Iodine belongs to the halogen family, which includes fluorine, chlorine, and bromine. Unfortunately, these elements have similar chemical makeups so they compete with iodine for absorption and can erroneously bind to iodine receptors, potentially leading to deficiency:

Fluoride (found in tap water and toothpaste)
Bromine (found in baked goods and flame retardants)
Chlorine (found in drinking water and pools)

This means that even if you consume iodine-rich foods, environmental exposure to these halogens could impact absorption.

Iodine’s Role in Glucose Metabolism and Insulin Sensitivity

Emerging research suggests that iodine may play a crucial role in glucose metabolism and insulin sensitivity. One potential mechanism involves iodine’s interaction with peroxisome proliferator-activated receptor-γ (PPAR-γ), a nuclear receptor that regulates lipid and glucose metabolism. PPAR-γ activation has been associated with improved insulin sensitivity by enhancing glucose uptake in peripheral tissues and modulating adipocyte differentiation. This suggests that iodine may contribute to metabolic health by influencing pathways that regulate insulin signaling.

However, the relationship between iodine and glucose metabolism is complex. While adequate iodine intake may support insulin function, excessive iodine consumption has been linked to cytotoxic effects on pancreatic beta cells, which are responsible for insulin secretion. High iodine levels can induce oxidative stress and apoptosis (cell death) in these cells, potentially impairing insulin production and increasing the risk of glucose dysregulation. Additionally, iodine excess has been associated with thyroid dysfunction, which can indirectly affect insulin sensitivity and glucose homeostasis through alterations in thyroid hormone levels.

These findings highlight the need to maintain optimal iodine intake, as both deficiency and excess can have metabolic consequences. Further research is needed to clarify the precise mechanisms by which iodine influences insulin function and to determine safe and effective dietary recommendations for individuals at risk of metabolic disorders.

Who Might Need More Iodine?

While iodine deficiency can affect anyone, certain populations are at higher risk:

Women with hormonal imbalances, endometriosis, or estrogen dominance
Pregnant and breastfeeding women (who require higher iodine intake)
Individuals with frequent exposure to fluoride, chlorine, and bromine
People with thyroid dysfunction or subclinical hypothyroidism
Those with blood sugar imbalances or insulin resistance

If you suspect iodine deficiency, a urinary iodine clearance test can help assess your levels. We only absorb 10% of iodine in the gut when levels are sufficient, so we want 90% excreted in the urine.

Key Thyroid Markers to Test

Relying on TSH alone isn’t enough to evaluate thyroid function. If you’re experiencing fatigue, weight gain, cold intolerance, or brain fog, consider testing:

Free T3 (FT3): The active thyroid hormone–shows how much thyroid hormone is being converted
Free T4 (FT4): The inactive form of thyroid hormone–shows how much thyroid hormone your thyroid is producing
Reverse T3 (rT3): Puts the breaks on thyroid hormone conversion–indicates stress or inflammation
Thyroid Antibodies (TPOAb, TgAb): Markers for autoimmune thyroid conditions like Hashimoto’s or Graves’ Disease

Before Increasing Iodine Intake

Before making changes to your iodine intake—whether through food sources or supplements—it’s essential to establish a strong foundation for overall health. Iodine metabolism is influenced by multiple factors, including stress, sleep, and nutrient status, so addressing these areas first can help your body utilize iodine more effectively. Consulting with a healthcare professional is also key to ensuring that supplementation is appropriate for your individual needs.

Consider these important questions before increasing iodine intake:

Am I eating enough?

Chronic under-eating can contribute to nutrient deficiencies, including iodine.

Am I under high stress?

Elevated stress levels increase cortisol, which can interfere with thyroid function and iodine metabolism.

Am I getting proper light exposure and balancing my circadian rhythm?

Sunlight helps regulate hormone production, including thyroid hormones, which depend on iodine.

Am I getting quality sleep?

Poor sleep can disrupt endocrine function, making it harder for your body to utilize iodine efficiently.

Am I going through a particularly demanding or stressful season of life?

Major life changes, illness, or intense physical demands can impact overall nutrient needs.

Am I deficient in other key minerals?

Iodine works in synergy with selenium, zinc, magnesium, and iron. Deficiencies in these minerals can impair iodine’s role in thyroid function and metabolism.

Since iodine is just one piece of the puzzle, it’s crucial to build a strong nutritional and lifestyle foundation before increasing intake. Addressing these factors first will help your body better absorb and utilize iodine while minimizing potential risks associated with excess or imbalance.

Safe Iodine Supplementation: What to Consider

Iodine supplementation isn’t a one-size-fits-all approach. Here are some key factors:

Start Low and Go Slow: Gradually increase iodine intake to allow your body to adjust.
Pair with Selenium: Selenium helps balance iodine metabolism and prevents thyroid inflammation.
Ensure Adequate Sodium Intake: Unrefined salt supports iodine transport.
Get Tested First: Urinary iodine testing and hair tissue mineral analysis (HTMA) can provide insights into your iodine status.

Symptoms of Iodine Deficiency

Signs of iodine deficiency can be subtle but may include:

Fatigue and sluggishness
Weight gain and slow metabolism
Cold intolerance
Dry skin and brittle nails
Hair thinning
Brain fog and poor concentration
Depression and mood swings
Irregular menstrual cycles

Best Dietary Sources of Iodine

To maintain healthy iodine levels, include these foods in your diet:

Seaweed (kelp, nori, wakame, dulse): The richest natural source of iodine.
Fish and shellfish (cod, tuna, shrimp, oysters): Packed with iodine and essential minerals.
Dairy products (milk, yogurt, cheese): Often fortified with iodine.
Eggs: A good source, especially from pasture-raised hens.

Final Thoughts

Iodine is an essential yet often overlooked nutrient that plays a pivotal role in thyroid function, hormone balance, metabolic health, and reproductive function. If you struggle with fatigue, hormonal imbalances, insulin resistance, or fertility concerns, it may be worth assessing your iodine levels and ensuring you’re getting enough from your diet or supplements. However, balance is key—too much iodine can be just as harmful as too little.

By understanding how iodine influences your health, you can take proactive steps to optimize your intake and support overall well-being.

Sources:

Anabelle Harari

wellspringnutrition.co

Iodine and Women’s Health: What You Need to Know

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