Abstract: Iodine is a prominent nutrient in thyroid hormone synthesis and is very important in operating a highly functioning thyroid. Thyroid health is critical during pregnancy as growing a new baby increases the demand on our thyroid. A sub-optimal thyroid leads to an increased risk of many pregnancy complications as well as a decrease in brain development and intelligence. Due to these significant consequences, iodine supplementation of at least 150 mcg is recommended. Iodine is present in food and can be found mainly in iodized salt, seaweed, seafood, and dairy products. Depending on your consistent consumption of these iodine-rich foods, you may need to adjust your dose of supplemental iodine during pregnancy.
What is Iodine? Why Do I Need It?
Iodine is an essential trace element that supports healthy thyroid and brain function. One of the most important functions of iodine is producing thyroid hormones and maintaining general endocrine health. The World Health Organization and American Thyroid Association acknowledge the importance of iodine in keeping the thyroid functioning optimally.
Iodine is used for thyroid hormone synthesis. When iodide, the form of iodine found in nature, enters the circulation, the thyroid gland concentrates it in appropriate amounts for hormone creation. Thyroid hormones are most widely recognized for their role in metabolism; however, they also influence many other systems in the body. The healthy adult with adequate iodine intake has about 15-20 mg of iodine, 70-80% of which is in the thyroid. Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These H4: hormones regulate many important biochemical reactions, including protein synthesis and enzymatic activity, and are critical determinants of metabolic activity.
Iodine also plays a role in immune response and can benefit the development of certain breast diseases, such as mammary dysplasia.
What About During Pregnancy, Why Is Iodine So Important?
Iodine sufficiency during pregnancy is extremely important for proper fetal development. After birth, sufficient iodine intake is also important for proper physical and neurological growth and maturation. A meta-analysis of 6,180 mother-child pairs from three birth cohorts in the Netherlands, Spain, and the United Kingdom found that verbal I.Q. assessed in children at 1.5 to 8 years of age was lower if their mothers had lower iodine status in their first trimester of pregnancy.
Thyroid Health and Pregnancy
During pregnancy, the amount of thyroid hormone needed increases by 50%. The thyroid gland increases hormone production significantly to account for both you and your baby. A non-optimally functioning thyroid will struggle even more during pregnancy.
To give a little background on the thyroid, let's start with the gland itself. Your thyroid is a tiny gland located at the front of your neck that produces several hormones. Thyroid-stimulating hormone (TSH), also known as thyrotropin, regulates thyroid function. The pituitary gland secretes this hormone to control thyroid hormone production and secretion, keeping hormone levels balanced and protecting the body from hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid). TSH secretion increases thyroidal iodine uptake and stimulates the synthesis and release of T3 and T4. In the absence of sufficient iodine, TSH levels remain elevated, leading to goiter, an enlargement of the thyroid gland that reflects the body's attempt to trap more iodine from circulation to produce more thyroid hormones.
Since it is not until mid-pregnancy (week 16-20) that the fetal thyroid gland is mature enough to produce its own hormones, the mother's thyroid is also operating for the baby. Even when the fetal thyroid gland is mature, maternal thyroid hormones are still influential, transferring across the placenta throughout pregnancy. These hormones are essential to the normal development of the baby.
Thyroid dysfunction is particularly problematic during pregnancy, leading to many complications. An underactive thyroid, or hypothyroidism, is the most common manifestation of thyroid dysfunction. Hypothyroidism may be associated with miscarriage, low birth weight, anemia, pregnancy-induced hypertension, preeclampsia, abruption placenta, postpartum hemorrhage, congenital circulation defects, fetal distress, preterm delivery, and poor vision development.
Furthermore, the baby's brain development is highly dependent on healthy thyroid hormone levels. Failure to create sufficient hormone levels to meet increased pregnancy demands can lead to irreversible brain damage, manifested in severity from neurological cretinism to minor or subtle deficits of intelligence and behavioral disorders. Thyroid hormones also lead to the proper development of the skeletal and central nervous system in fetuses and infants.
According to some research, lack of nausea or morning sickness in the first trimester can be a sign of underactive thyroid and/or iodine deficiency.
Nutrition For Thyroid Health
Does what I eat influence thyroid function? It does! And iodine is the most important nutrient. Thyroid hormones can not be made without it, and 57% of pregnant women in the U.S. are deficient in iodine. On top of that, the need for iodine doubles during pregnancy due to the increase in thyroid hormone synthesis by approximately 50%. Pregnant women who do not regularly consume seafood and dairy products and do not obtain iodine from supplements are at significant risk of being deficient in iodine.
Observational studies show a connection between insufficient iodine intake during pregnancy and impaired maternal thyroid function leading to babies born with mild intellectual impairment. The World Health Organization (WHO) considers iodine deficiency the single most important preventable cause of brain damage worldwide.
What Form of Supplementation is Best?
In dietary supplements, iodine is often present as potassium iodide or sodium iodide. Supplements containing kelp, a seaweed that contains iodine, are also available. A small study indicated that people absorb potassium iodide almost entirely (96.4%).
How Much Iodine Do You Need During Pregnancy?
During pregnancy, the RDA for iodine increases from 150 to 220 mcg/day. Surveys indicate that many pregnant women in the United States might consume insufficient iodine even if they do not have signs or symptoms of overt iodine deficiency.
Several national and international groups recommend iodine supplementation during pregnancy. The American Thyroid Association recommends that women who are pregnant or planning to become pregnant should supplement their diet with 150 mcg/day of iodine in the form of potassium iodide. Similarly, the American Academy of Pediatrics recommends taking a daily supplement of at least 150 mcg of iodine per day using iodized salt. The WHO attempts to make a more complex recommendation depending on location. If you live in a country with sufficient iodized salt distribution, the WHO suggests that supplementation may not be necessary. However, for women living in countries with weak, sporadic, or uneven iodized salt distribution, the WHO recommends iodine supplementation for all women of childbearing age to achieve a total iodine intake of 150 mcg/day. The goal is a total of 250 mcg/day from both supplements and dietary sources.
Please note that although the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) Global Network estimates that the proportion of U.S. households with access to iodized salt exceeds 90%, the data regarding actual usage is limited. The contribution of iodized salt to the overall iodine sufficiency of the U.S. population is uncertain.
However, due to the note above, we believe it is best to follow the recommendations for iodine supplementation and dietary sources in addition to any iodized salt intake.
Am I Getting It From Food?
Yes! Particularly from iodized salt. However, iodine from iodized salt does decline with storage, especially in high humidity areas. There is such a thing as iodized milk, and even bread in the United States can be a good source of iodine.
Seaweed, such as kelp, nori, kombu, and wakame, is one of the best food sources of iodine. Other good food sources include fish and other seafood, as well as eggs. Asparagus, beets, and cranberries contain iodine but not a significant amount. Most fruits and vegetables are poor sources of iodine, and the amounts they contain are affected by the iodine content of the soil, fertilizer use, and other farming practices.
Dairy contains iodine. However, the amount of iodine in dairy products varies by the cow and its feed. Some cows receive iodine feed supplements. Iodophor sanitizing agents can also be used to clean the cows and the milk-processing equipment, lowering iodine amounts in the associated dairy products. These variables cause a wide range of iodine in nonfat milk (38 to 159 mcg per cup, with an average of 85 mcg per cup). However, pregnant women who do not consume dairy products may be particularly at risk of iodine insufficiency.
One issue to consider in getting iodine from food is the consumption of goitrogens, which can block iodine uptake in the thyroid gland. These include soy products and raw cruciferous vegetables, such as cabbage, kale, and broccoli. However, cooking these vegetables eliminates the goitrogen iodine absorption issue.
How Can I Tell If I Am Getting Enough Iodine?
According to the WHO, a median urinary iodine concentration of 150-249 mcg/L indicates adequate iodine nutrition during pregnancy. Urinary markers less than 150 mcg/L are considered insufficient.
Prenatal Vitamin Brands: What's the Iodine Amount and Type in Popular Prenatal Brands?
Name of the Prenatal | Amount | Type
Name of the Prenatal
|Parsley Health Prenatal:||225 mcg||(potassium iodide)|
|Modern Fertility Prenatal:||190 mcg||(potassium iodide)|
|Ritual Prenatal:||150 mcg||(potassium iodide)|
|FullWell Prenatal:||250 mcg||(from Kelp)|
|Perelel: Conception Support and All Trimester Packs:||150 mcg||(potassium iodide)|
|NatureMade Prenatal Multi + DHA:||150 mcg||(potassium iodide)|
|Seeking Health: Optimal Prenatal:||250 mcg||(potassium iodide)|
|Designs for Health: Prenatal Pro:||200 mcg||(potassium iodide)|
With an RDA during pregnancy of 220 mcg/day, many supplements provide the total daily need. Furthermore, multiple governing organizations approve 150 mcg/day of supplemental iodine. FullWell is the outlier in terms of supplemental form, utilizing the mineral's very natural kelp form. Others use potassium iodide, which is supported by research showing that this form gets absorbed almost completely, approximately 96.4%. If you are a vegan, avoid dairy products, and limit your iodized salt intake, it may be advisable to incorporate a supplement above with a higher dose of iodine.
- Iodine - Health Professional Fact Sheet. Accessed May 27, 2022. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
- Henjum S, Aakre I, Lilleengen AM, et al. Suboptimal Iodine Status among Pregnant Women in the Oslo Area, Norway. Nutrients. 2018;10(3):280. doi:10.3390/nu10030280
- Censi S, Watutantrige-Fernando S, Groccia G, et al. The Effects of Iodine Supplementation in Pregnancy on Iodine Status, Thyroglobulin Levels and Thyroid Function Parameters: Results from a Randomized Controlled Clinical Trial in a Mild-to-Moderate Iodine Deficiency Area. Nutrients. 2019;11(11):2639. doi:10.3390/nu11112639
- Verhagen NJE, Gowachirapant S, Winichagoon P, Andersson M, Melse-Boonstra A, Zimmermann MB. Iodine Supplementation in Mildly Iodine-Deficient Pregnant Women Does Not Improve Maternal Thyroid Function or Child Development: A Secondary Analysis of a Randomized Controlled Trial. Front Endocrinol. 2020;11:572984. doi:10.3389/fendo.2020.572984
- Council on Environmental Health, Rogan WJ, Paulson JA, et al. Iodine deficiency, pollutant chemicals, and the thyroid: new information on an old problem. Pediatrics. 2014;133(6):1163-1166. doi:10.1542/peds.2014-0900
- Eastman CJ, Ma G, Li M. Optimal Assessment and Quantification of Iodine Nutrition in Pregnancy and Lactation: Laboratory and Clinical Methods, Controversies and Future Directions. Nutrients. 2019;11(10):E2378. doi:10.3390/nu11102378
- Murcia M, Espada M, Julvez J, et al. Iodine intake from supplements and diet during pregnancy and child cognitive and motor development: the INMA Mother and Child Cohort Study. J Epidemiol Community Health. 2018;72(3):216-222. doi:10.1136/jech-2017-209830
- Lumen A, George NI. Estimation of iodine nutrition and thyroid function status in late-gestation pregnant women in the United States: Development and application of a population-based pregnancy model. Toxicol Appl Pharmacol. 2017;314:24-38. doi:10.1016/j.taap.2016.10.026
- Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet Lond Engl. 2013;382(9889):331-337. doi:10.1016/S0140-6736(13)60436-5
- Nichols L. Real Food for Pregnancy: The Science and Wisdom of Optimal Prenatal Nutrition. First edition. Lily Nichols; 2018.