Reviewed by Evan Lewis, PhD. Last updated 10 August 2026.
Iodine status affects how quickly women conceive. In a prospective US cohort, women whose iodine-creatinine ratio was below 50 micrograms per gram, moderate to severe deficiency, had a 46% reduction in fecundity. The authors concluded that delays occur at iodine levels common in the USA.
The connection between iodine and fertility is more significant than most women realize. In NHANES 2011 to 2014, the median urinary iodine concentration among U.S. women of reproductive age was 110 µg/L (Herrick et al., Nutrients, 2018), not far above the 100 µg/L mark used to judge whether a population's iodine intake is adequate.
This essential mineral is vital for thyroid hormone production, metabolic regulation, and reproductive health. Whether you are actively trying to conceive or planning for the future, understanding how iodine fertility research applies to your health could be one of the most important steps you take.
Seafood, iodized salt, dairy, and some vegetables contain iodine, yet dietary shifts, particularly toward plant-based eating, have left many women short on this micronutrient.
What Is Iodine Deficiency?
It is what happens when the body does not take in enough iodine to support the production of thyroid hormones, T3 (triiodothyronine) and T4 (thyroxine). These hormones regulate metabolism, energy production, body temperature, and fetal brain development.
Without adequate iodine, the thyroid gland cannot function properly, potentially leading to goiter (thyroid enlargement), hypothyroidism, and in severe cases, significant developmental complications in newborns.
Iodine deficiency is particularly relevant among women of reproductive age and during pregnancy, making adequate daily intake especially important for those hoping to conceive.
Why Does Iodine Matter for Fertility?
Because the thyroid sits upstream of ovulation. Adequate iodine intake is foundational to thyroid health, and thyroid health is foundational to reproductive function. The thyroid gland regulates hormones that influence ovulation, menstrual cycle regularity, and the uterine environment needed to sustain a healthy pregnancy.
The standard daily intake figures, as set out in Delange and Zimmermann's iodine chapter in Endotext, are:
- 150 mcg/day for adults, including women of reproductive age
- 220 mcg/day during pregnancy by the IOM figure, or 250 mcg/day by the WHO figure
- 290 mcg/day during lactation by the IOM figure, or 250 mcg/day by the WHO figure
The same reference states that women planning a pregnancy or already pregnant should take a daily oral supplement containing 150 mcg of iodine in the form of potassium iodide. Ideally that starts three months before conception and continues through pregnancy and breastfeeding.
What Does the Research Say About Iodine and Conception?
It says the delay is measurable. A prospective cohort study published in Human Reproduction in 2018 by Mills and colleagues at the U.S. National Institute of Child Health and Human Development followed 501 women who had discontinued contraception within two months in order to become pregnant.
What they found:
- The group whose iodine-creatinine ratios were below 50 µg/g, described in the paper as moderate to severe deficiency, had a 46% reduction in fecundity compared with women in the adequate range
- The paper's own conclusion, verbatim: "Significant delays in becoming pregnant occur at iodine concentrations that are common in women in the USA and parts of Europe"
The stakes carry past conception. In a large UK birth cohort, children of mothers with inadequate iodine status in early pregnancy were more likely to fall in the lowest quartile for verbal IQ, reading accuracy and reading comprehension, which is why the advice is to sort iodine out before conception rather than after.
What Are the Symptoms of Iodine Deficiency?
Mostly the quiet, easily-blamed-on-something-else ones. Iodine deficiency can show up in numerous ways, many of which touch fertility and reproductive outcomes:
- Persistent fatigue and low energy
- Unexplained weight gain
- Dry skin or hair loss
- Cold intolerance
- Irregular or absent menstrual cycles
- Difficulty conceiving
- Increased risk of miscarriage, stillbirth, or preterm delivery
- Low infant birth weight
- Thyroid enlargement (goiter)
These reproductive consequences, from delayed conception to pregnancy complications, underscore why monitoring and addressing iodine status before and during pregnancy is so important.
Who Is Most at Risk of Low Iodine?
Anyone whose diet has quietly dropped the main sources. Several factors can increase a woman's risk:
- Following a vegan or vegetarian diet (limiting seafood and dairy)
- Living in a region where iodized salt is not commonly used
- Family history of thyroid disorders
- Pregnancy or breastfeeding, which dramatically increase iodine demand
- Excessive consumption of goitrogenic foods (raw cruciferous vegetables, soy) that can interfere with iodine uptake
- Kidney conditions that affect iodine retention
Reproductive specialists have pointed to the rise of plant-based eating as one contributor to declining iodine intake among women of childbearing age, since seafood and dairy are the two dietary sources most often dropped.
Does Radioactive Iodine Affect Fertility?
Temporarily, in most cases. Radioactive iodine (RAI) therapy, typically used for hyperthyroidism or thyroid cancer, can have a short-term impact, but long-term fertility is generally preserved with proper timing.
Here is what the current evidence indicates:
- Temporary menstrual irregularity may occur in the months immediately following RAI treatment
- Most clinical guidelines recommend waiting 6 to 12 months after RAI before attempting to conceive, allowing thyroid hormone levels to fully stabilize
- Long-term studies have not demonstrated that RAI causes permanent infertility in women
- Pregnancy outcomes in women who waited the appropriate period following RAI appear to be broadly comparable to the general population
- Post-RAI hypothyroidism, if left untreated, can impair fertility, and thyroid hormone replacement therapy typically resolves this
If you have undergone RAI therapy and are planning a pregnancy, consult your endocrinologist and reproductive specialist to confirm your thyroid hormone levels are optimized before conception.
How Is Iodine Deficiency Diagnosed?
Through urine and thyroid bloodwork, not guesswork. Healthcare providers use several tools:
- Urinary Iodine Concentration (UIC), the most commonly used population-level screening measure
- Thyroid Function Tests (TFTs), measuring TSH, Free T4 (FT4), and Free T3 (FT3)
- Physical examination for signs of goiter or thyroid irregularity
- Dietary and medical history review to identify risk factors
Early identification allows for timely action, which matters most for women planning to conceive or in the early stages of pregnancy when fetal brain development begins.
Iodine Supplementation: Key Considerations
When dietary sources alone are insufficient, supplementation is a practical way to support iodine levels. Important considerations include:
- Most standard prenatal vitamins contain approximately 150 mcg of iodine, so confirm your prenatal vitamin's label, as not all include iodine
- Supplementation ideally begins at least three months before attempting conception
- Iodine intake should be maintained through pregnancy and the full breastfeeding period
- Both deficiency and excess can cause problems. The tolerable upper intake level for adults is 1,100 mcg a day, so balance is essential
One nuance worth noting: women who underwent hysterosalpingography (HSG) with oil-soluble contrast medium showed elevated urinary iodine concentrations that sometimes persisted for months, so iodine status is worth rechecking after certain fertility diagnostic procedures.
What Are the Best Dietary Sources of Iodine?
Seafood, dairy, eggs and iodized salt, in that order for most diets. To support both fertility and overall thyroid health, prioritize:
- Seaweed and kelp, among the highest natural sources available, and the easiest to overshoot
- Fish and shellfish (cod, tuna, shrimp, salmon)
- Dairy products (milk, yogurt, cheese)
- Eggs
- Iodized table salt, noting that sea salt and kosher salt are typically not iodized
- Fortified breads and cereals
Is Topical Iodine the Same Conversation?
No, and the two get run together constantly. Everything above is about iodine you eat, which is a thyroid and nutrition question and belongs with your doctor and a prenatal supplement.
Iodine applied to skin is a different subject with a different purpose. IodinePure EZ Clear Skin is a two-ingredient aqueous iodine mist, elemental iodine and pure water, listed with Health Canada as a cosmetic and used as a daily hygiene step that supports the look of clearer skin. It is not a supplement, it does not change your dietary iodine intake, and it is not a fertility product. If you are pregnant or trying to conceive, ask your provider before using any topical iodine.
Conclusion
The relationship between iodine and fertility is supported by real clinical research. From regulating ovulation-critical thyroid hormones to the cognitive outcomes measured in the children of iodine-deficient mothers, adequate iodine is one of the most practical nutritional factors a woman can address when planning a pregnancy.
Whether your iodine status is affected by dietary choices, a history of thyroid treatment, or simply a gap in awareness, the evidence points one way: sorting out your iodine intake, ideally several months before conception, supports reproductive health outcomes.
Talk to your healthcare provider about testing your iodine and thyroid hormone levels, and discuss whether supplementation is appropriate for your situation.
Journal Reference
Mills, J.L., Buck Louis, G.M., Kannan, K., Weck, J., Wan, Y., Maisog, J., Giannakou, A., Wu, Q., Sundaram, R. (2018). Delayed conception in women with low-urinary iodine concentrations: a population-based prospective cohort study. Human Reproduction, 33(3):426-433. PMID 29340704.
Herrick, K.A., Perrine, C.G., Aoki, Y., Caldwell, K.L. (2018). Iodine Status and Consumption of Key Iodine Sources in the U.S. Population with Special Attention to Reproductive Age Women. Nutrients, 10(7):874. PMC6073695.
Bath, S.C., Steer, C.D., Golding, J., Emmett, P., Rayman, M.P. (2013). Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children. The Lancet. PMID 23706508.
Delange, F., Zimmermann, M. The Iodine Deficiency Disorders. Endotext, NCBI Bookshelf NBK285556.
Additional Resources
For further reading, the American Thyroid Association publishes resources on iodine deficiency and its implications for pregnancy and fertility at thyroid.org.
Frequently Asked Questions
How does iodine affect fertility?
Iodine supports the production of thyroid hormones, which regulate ovulation and menstrual cycle regularity. In a 2018 prospective cohort of 501 women trying to conceive, those with moderate to severe iodine deficiency, an iodine-creatinine ratio below 50 micrograms per gram, had a 46% reduction in fecundity compared with women in the adequate range.
How much iodine should women take to support fertility?
The daily requirement for adults is 150 mcg, and women planning or in pregnancy are advised to take a daily supplement containing 150 mcg of iodine as potassium iodide, ideally starting three months before conception. Requirements rise to 220 mcg a day in pregnancy by the IOM figure, or 250 by the WHO figure.
Does radioactive iodine affect fertility?
Radioactive iodine (RAI) therapy can temporarily disrupt menstrual regularity and thyroid hormone levels. Most clinical guidelines recommend waiting 6 to 12 months after RAI before attempting to conceive. Long-term studies have not shown RAI to cause permanent infertility in women who wait the appropriate period before conceiving.
What are the signs of iodine deficiency that may affect reproductive health?
Signs of iodine deficiency that may impact fertility include irregular or absent menstrual periods, difficulty conceiving, fatigue, unexplained weight gain, and cold intolerance. During pregnancy, iodine deficiency is associated with increased risk of miscarriage, stillbirth, preterm birth, and developmental issues in the baby.
Can you get enough iodine from diet alone?
Many women can meet their iodine needs through a diet rich in seafood, dairy, eggs, and iodized salt. However, women following plant-based diets or avoiding salt may not get sufficient iodine from food alone and may benefit from a daily supplement containing 150 mcg of iodine, particularly during the preconception and pregnancy periods.
Evan Lewis, PhD, specializes in natural and nutritional therapies for the prevention and management of chronic diseases and their complications. His research spans chronic disease, diabetes complications, clinical nutrition, and nerve health, including the development of topical iodine approaches for foot care and wound health. IodinePure products are listed with Health Canada as cosmetics.
