When it comes to optimising fertility, iodine plays a crucial role in supporting thyroid function and ovarian health. Research suggests that iodine is actively absorbed by the ovaries and endometrium, potentially aiding implantation. This is not only evident in humans but also in animals, where iodine supplementation is commonly used to restore ovulatory function.

Are You Deficient in Iodine?

Iodine deficiency can manifest in various ways, including:

• Cystic tissue development (such as ovarian cysts, fibrocystic breasts, and breast lumps)
• Breast tenderness, particularly in the luteal phase
• Irregular or anovulatory menstrual cycles
• Thyroid abnormalities
• Weakened immune function

However, the only definitive way to determine iodine deficiency is through testing.

The Challenges of Measuring Iodine Intake

Determining whether you need additional iodine can be tricky. Iodine content is rarely listed on food labels or nutrient databases, and levels vary depending on where and how food is grown or produced. Additionally, iodine testing is not routine, making it difficult to assess individual needs. Some functional medicine practitioners offer iodine testing, with urinary iodine concentration (UIC) being the most common assessment method. UIC levels under 150 mcg/L indicate deficiency, while levels between 150 and 249 mcg/L are considered adequate.

Iodine and Miscarriage Risk

Iodine deficiency is a well-established risk factor for pregnancy loss and maternal thyroid complications. Prioritising iodine intake before conception supports overall fertility and ensures adequate stores for pregnancy. While many assume that iodine deficiency is rare in developed countries due to salt fortification, studies indicate otherwise—44% of women in developed nations have insufficient iodine levels.

A study examining time to conception in the US and Europe found that women with low urinary iodine levels experienced a 46% reduction in fertility. Additionally, 28% of the iodine-deficient group failed to conceive within a year, compared to only 12.5% of those with adequate iodine levels.

Since iodine requirements increase during pregnancy and breastfeeding, optimising intake preconceptionally is beneficial.

How Much Iodine Do You Need?

The recommended daily allowance (RDA) for iodine is:

• 150 mcg for non-pregnant adults
• 220–290 mcg during pregnancy and lactation (WHO recommends 250 mcg for pregnancy)

However, many women fail to meet even the lower threshold, especially those who avoid seafood, dairy, and eggs. Interestingly, in Japan—where seaweed consumption is high—average iodine intake ranges from 1,000 to 3,000 mcg per day, with no observed adverse effects on pregnancy outcomes.

Best Food Sources of Iodine

To naturally boost iodine intake, focus on iodine-rich foods such as:

• Seafood: Seaweed, scallops, cod, prawns, sardines, salmon
• Dairy: Milk, cheese, yoghurt
• Eggs: A significant source of iodine for non-seafood eaters
• Vegetables & Fruits: Asparagus, beets, cranberries
• Iodised Salt: Iodised salt is a helpful but sometimes unreliable source, as iodine content decreases with storage

Studies indicate that dairy intake has a profound impact on iodine status, particularly for breastfeeding women. Women who consume dairy regularly have significantly higher iodine levels in breast milk compared to women who do not.

How to Include More Seaweed in Your Diet

Seaweed is one of the best natural sources of iodine, making it an excellent addition to a fertility-friendly diet. Here are some simple ways to incorporate more seaweed into your meals:

• Sprinkle seaweed flakes (such as dulse, wakame, or nori) over salads, soups, eggs, and roasted vegetables for an easy iodine boost.
• Stir into broths, stews, or miso soup to enhance both flavour and nutrition.
• Blend a small amount of dulse flakes into smoothies—they have a mild taste and won’t overpower other ingredients.
• Use seaweed as a topping for rice bowls, avocado toast, or sushi rolls.
• Snack on seaweed sheets—they’re light, crispy, and naturally rich in iodine.
• Make a seaweed and nut snack mix, combining crumbled nori with almonds, cashews, or seeds for a crunchy, nutrient-dense snack.

Adding seaweed to your diet is an easy and delicious way to increase iodine intake to support thyroid function, hormone balance, and fertility health. If you don’t regularly consume seafood, dairy, or eggs, seaweed can be especially beneficial for maintaining adequate iodine levels.

Factors That Affect Iodine Absorption

Certain foods and environmental factors can interfere with iodine metabolism, including:

• Goitrogens: Found in soy and raw cruciferous vegetables (e.g., kale, cabbage, broccoli). Cooking or fermenting these vegetables reduces their impact on iodine absorption.
• Halogens: Chemicals such as chlorine, fluorine (fluoride), and bromine found in non-stick cookware, stain-resistant treatments, and flame retardants can hinder iodine metabolism.

Iodine and Plant-Based Diets

Iodine deficiency is particularly common among vegetarians and vegans due to the lack of iodine-rich foods in plant-based diets. A UK study found that:

• Vegan women consumed an average of just 24 mcg of iodine per day
• Vegetarians averaged 91 mcg/day
• Omnivores consumed 113 mcg/day

All groups fell short of the 150 mcg RDA, but vegans were the most affected. Countries like Iceland have seen a surge in iodine deficiency due to declining fish, dairy, and egg consumption. For those following plant-based diets, including seaweed in meals is essential to prevent deficiency.

Should You Take an Iodine Supplement?

While dietary sources are preferred, supplementation may be necessary for some individuals. Unfortunately, about half of prenatal vitamins do not contain iodine. Reputable professional organisations—including the American Thyroid Association, European Thyroid Association, and the Endocrine Society—recommend a minimum 150 mcg iodine supplement during preconception, pregnancy, and lactation.

If supplementation is needed, work with a nutritionist to ensure iodine intake is balanced with other synergistic nutrients like selenium, iron, zinc, vitamins A, C, D, and E and B vitamins.

Key Takeaways on Iodine for Fertility

• Iodine is essential for fertility: It supports ovarian function and implantation.
• Deficiency is common: Despite salt fortification, many women, especially those avoiding seafood, dairy, and eggs, have insufficient iodine levels.
• Iodine deficiency is linked to delays in conception: Women with low iodine levels are significantly less likely to conceive within a year.
• Iodine requirements increase during pregnancy: Insufficient intake raises the risk of miscarriage, preeclampsia, and preterm birth.
• Food sources matter: The best iodine-rich foods include seaweed, seafood, eggs, and dairy.
• Some people may need supplementation: Particularly vegans, vegetarians, and those with low dietary iodine intake.
• Iodine interacts with other nutrients: Ensuring adequate selenium, zinc, and vitamins A, C, D, and E enhances iodine’s effectiveness.

Final Thoughts on Iodine for Fertility

Iodine is a crucial yet often overlooked nutrient for fertility. While public health measures aim to prevent severe deficiency, many women still consume insufficient iodine, which can negatively impact fertility and pregnancy. Focusing on iodine-rich foods, testing iodine status, and supplementing when necessary can help optimise fertility and improve overall reproductive health.

If you’re trying to conceive, now is the time to assess your iodine intake and ensure you’re giving your body the best possible support.