Iodine Intake During Lactation
by Anne Eglash MD, IBCLC, FABM
This week’s article is a comprehensive review of the iodine intake and its importance during pregnancy and lactation.
Iodine is an essential element required for production of thyroid hormone. Normal thyroid function is crucial for normal metabolism for all humans, and optimal brain and other tissue growth and development in fetuses and children. Either excessive or insufficient iodine intake can cause low thyroid function. Infants born to a mother with severe iodine deficiency are at significant risk for mortality, intellectual disabilities, and/or problems with growth, hearing, and speech. Even mild iodine deficiency during pregnancy increases the risk of lower IQ and attention deficit disorder in children.
The US Centers for Disease Control recommends an iodine intake of 150µg/day before pregnancy, 220 µg/day during pregnancy, and 290 µg/day during lactation. Because of increased iodine requirement, pregnant and lactating individuals are at higher risk for iodine deficiency.
At the time of birth, infants have approximately 2 days of stored iodine, after which time they depend on dietary iodine. Iodine levels in human milk depend on maternal dietary intake.
The breastmilk concentration of iodine varies from day to day, depending on the daily diet.
Natural sources of dietary iodine include seaweed, fish, other seafood, and eggs. Dairy products may also have iodine, depending on the amount of iodine in supplements given to cows, and the iodine in the sanitizing agents used to clean the cows and the pumping equipment. Fruits and vegetables tend to be poor sources of iodine, as the levels depend on the amount of iodine in the water and soil, which are often low.
The primary dietary source of iodine in the general population is iodized salt. Just 1 teaspoon (6 grams) of iodized salt contains 250µg of iodine, meeting the iodine requirements for pregnant and lactating people. Although adding iodine to salt is a public health measure in most countries worldwide, it is often not required. In the USA, the Food and Drug Administration (FDA) states that iodide (the typical form of iodine) may be added to table salt, and table salt without added iodide must be labelled “This salt does not supply iodide, a necessary nutrient.”
Gourmet sea salts and kosher salt, increasingly popular in cooking, do not have natural or added iodine. Consumer Labs evaluated the metal and mineral content of Himalayan, Mediterranean Sea Salt, Hawaiian Sea Salt, and other designer salts, and found a variable amount of essential minerals and heavy metals, but no significant natural iodine.
A substantial percentage of pregnant and lactating women in the USA are considered to have insufficient iodine intake. For this reason, both the American Academy of Pediatrics and the American Thyroid Association recommend that pregnant or lactating women take a daily vitamin or prenatal supplement that contains 150mcg. The FDA does not require any particular ingredient in supplements, so some multivitamins have iodide, and some do not. A 2019 study found that only 58% of prenatal vitamins contain iodine.
Excess iodine supplementation can also cause thyroid disease and is not safe for anyone pre-pregnancy or during pregnancy/lactation.
- People who do not use iodized salt.
- Vegans who use natural, non-iodized salt and eat no dairy products or seafood.
- People with a high intake of cabbage, cauliflower, and/or broccoli who do not use iodized salt.
- Breastfed infants older than 6 months with low breastmilk intake, no formula, and who have little added salt in their diet.
- People who are iron deficient.
See the Answer
Pregnant and lactating individuals should be encouraged to take a prenatal vitamin that has 150µg of iodide, to avoid even mild iodine deficiency. The intake of 150µg as a supplement assumes that people will also ingest iodine in their diet from seafood, fish, dairy products and/or iodized salt. However, if the diet is void of these animal products, and natural salts are used in cooking, then a supplement containing 150µg is insufficient. The easiest fix is to use iodized salt in one’s diet.
Foods that contain substances called ‘goitrogens’ include cauliflower, broccoli, kale, cabbage, sweet potatoes and turnips. Goitrogens are substances that interfere with uptake of iodine into the thyroid gland. These foods should not be avoided, since they are part of a healthy plant-based diet. Cooking, steaming, or fermenting these vegetables can reduce the goitrogens, and taking adequate iodized salt limits the effect of goitrogens.
Soy and millet can impair the body’s process of using iodine to make thyroid hormone. This process can also be impaired in people with iron deficiency, as iron is also needed in the manufacturing of thyroid hormone.
Yoo-Mi Chung
Korean mothers have the opposite issue of excessive iodine uptake. It might be important to keep this in mind when consulting Korean breastfeeding mothers.
https://pubmed.ncbi.nlm.nih.gov/19808851/
Subclinical hypothyroidism in Korean preterm infants associated with high levels of iodine in breast milk
Abstract
Context: The dietary iodine intake of lactating women has been reported to be high in Korea.
Objectives: The aim of this study was to assess iodine balance and to determine its relationship with thyroid function in preterm infants.
Design: Thyroid functions of preterm infants born at 34 wk gestation or less were evaluated in the first (n = 31) and third (n = 19) weeks. Mothers’ breast milk (BM) and random urine samples of infants were taken on the same days for thyroid function tests.
Results: Iodine concentrations in BM were very high (198-8484 microg/liter), and one third of the infants had an iodine intake of more than 100 microg/kg per day at the third week after birth (excessive iodine intake group). At that time, the levels of TSH were positively correlated with urinary iodine (r = 0.622; P = 0.004). The frequencies of subclinical hypothyroidism were high in the excessive iodine intake group at the third and sixth weeks. The estimated daily iodine intake at the third week (51.2 +/- 45.5 vs. 149.0 +/- 103.8 microg/kg per day; P = 0.033), urinary iodine at the third week (913.2 +/- 1179.7 vs. 1651.3 +/- 1135.2 microg/liter; P = 0.051), and estimated daily iodine intake at the sixth week (32.8 +/- 35.5 vs. 92.1 +/- 51.2 microg/kg per day; P = 0.032) were significantly higher in infants with subclinical hypothyroidism than in controls.
Conclusions: Excessive iodine intake from BM contributed to subclinical hypothyroidism in these preterm Korean infants.
IABLE
Thank you for posting this. Yes, excessive iodine intake can also cause thyroid dysfunction, and is a cause of goiters in some parts of the world. High iodine intake can also be associated with papillary thyroid cancer. I didn’t go into detail regarding excessive intake, to prevent this article from being too lengthy. The most iodine-rich food is seaweed, and seaweed varies considerably in its iodine content. Frequent intake of seaweed that is high in iodine can cause high iodine levels in breastmilk. Here is an article on high iodine intake in Korea- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8258329/pdf/enm-2021-1005.pdf
YOOMI CHUNG
Thank you for the article.
Laura Corsig
Thank you, Dr. Eglash! I am a hospital-based lactation consultant and my colleagues and I have been considering the nutrition education that we provide (or lack there of) to our prenatal and lactating parents.
We currently teach the basic, “continue PNV during lactation.” But we wonder if we should provide more specifics? I am interested to know if you or anyone reading this recommends a specific brand(s) of PNV or ingredient list? And if so, do you recommend to all pregnant/lactation or only if they have risk factors?
I appreciate any wisdom you can share.
Thanks!
IABLE
Hi Laura, there is not a one-size-fits all vitamin for everyone, just like there is not 1 type of diet that is best for everyone. The type of vitamin supplementation and amount will depend on the person’s diet and health condition(s). For example, people with celiac or gastric bypass will have different vitamin needs than someone who has no underlying GI issues. People who eat certain diets, such as a vegan diet, or a diet without fish, would benefit from added vitamin supplementation beyond what someone who eats meat and fish would need. It would be lovely if everyone could see a nutritionist for individual counseling!