Dr. Tanya Lee, H.BSc, ND

thyroid pregnant

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Thyroid health is an extremely important area to monitor for both fertility and pregnancy. It is commonly known in the medical community that thyroid function can be thrown off balance during pregnancy, and it is estimated that 2-4% of women during pregnancy has thyroid dysfunction.1 Thyroid conditions are the second most common glandular problem in women of childbearing age and it is estimated that 8-12% of pregnancy losses are due to thyroid problems.2 It is also important to note that 10% of infertility cases are due to the presence of thyroid antibodies, despite laboratory screening values suggesting that thyroid function is normal.2 This makes it extremely important to screen all aspects of thyroid health, not just the basic screening tests when trying to conceive and during pregnancy, especially when symptoms are present. Common symptoms associated with low thyroid function include fatigue, hair loss, dry skin, weight gain, depression, and constipation. Common symptoms of overactive thyroid function include palpitations, weight loss, anxiety, and trouble sleeping. Outcomes of thyroid dysfunction during pregnancy can include miscarriage, preterm delivery, intrauterine growth retardation, and decreased IQ of the child.1

In order to improve thyroid health before and during pregnancy, there are two important minerals you can incorporate into your diet that can dramatically and positively affect thyroid function.


Iodine is a building block of thyroid hormones and is an important mineral for thyroid regulation. Both hypothyroid and hyperthyroid problems can be attributed to low iodine intake. Iodine deficiency is considered uncommon in our society due to the supplementing regular salt with iodine. As people are becoming more conscious of the negative effects of salt on blood pressure, avoiding salt has become the norm. This contributes to deficient iodine intake as other sources of iodine are not abundant in our North American diets. Other main sources of iodine-containing food include sea vegetables, such as seaweed, kelp and dulce. Scallops are also a great source of iodine, as well as shrimp, salmon and sardines. Notice the pattern of sea origin from these foods. The recommended daily allowance (RDA) of iodine is 220 mcg daily in pregnancy, though many health professionals argue this dose is too low, especially for those with pre-existing thyroid disorders. The upper limit of iodine in pregnancy and lactation is 1100 mcg, meaning that these levels have been found to unlikely cause immediate adverse effects, but dosing beyond this may lead to further thyroid problems.3 For pregnancy, due to the requirements of the growing baby, I typically recommend increasing iodine intake beyond the RDA; some individuals may need higher dosing, while others will aggravate and due to the uncertainty of what is considered too much iodine in the daily diet, any supplementation above the RDA should be recommended by a qualified healthcare provider. With a North American standard diet, the RDA of iodine is very difficult to achieve, therefore incorporating these foods can be a great way to keep the thyroid stable. For reference 1 tbsp of sea vegetables = 750mcg of iodine, 4 ounces of scallops = 125mcg of iodine, 1 cup of yogurt = 71 mcg of iodine.

For reference 1 tbsp of sea vegetables = 750mcg of iodine, 4 ounces of scallops = 125mcg of iodine, 1 cup of yogurt = 71 mcg of iodine.4


Selenium is an essential mineral used to help convert inactive thyroid hormone to active thyroid hormone. This mineral is also important for reducing thyroid antibodies, which are found autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves disease. Just like iodine, selenium is a mineral found abundantly in seafood such as tuna, salmon, shrimp, cod, but is also found in other meats such as lamb, beef and poultry. The RDA of selenium is 60mcg in pregnant women, though in thyroid conditions, we recommend increasing the dosage to at least 100-200mcg daily. The upper limit of selenium is 400mcg daily.5 Selenium is relatively safer than iodine to supplement on top of your prenatal vitamin and foods, though it is still recommended that when dosing higher amounts of selenium, consulting with a qualified healthcare provider is recommended to know exactly how much you should be taking for your individualized health concerns. For reference, 4 ounces of tuna = 123 mcg of selenium, turkey = 34mcg of selenium, and 1 cup of barley = 23mcg of selenium, 6-8 Brazil nuts = 544 mcg of selenium.5,6

Thyroid conditions are very common disorders in North America. Though exact reasons as to this prevalence have not been solidified, many studies and health care providers observe that the lack of dietary nutrients which support the thyroid are a large contributing factor. Being conscious of increasing selenium and iodine in your daily diet to reach the RDA is one way of improving thyroid function. Any additional supplementation is strongly recommended to be supervised by a qualified physician who has knowledge of proper use of high dose vitamins and minerals and a strong knowledge of nutritional biochemistry.

HCM HSDr. Tanya Lee, N.D. received her Honours Bachelor of Science degree in Biochemistry and Biomedical Sciences from McMaster University, and was trained as a Naturopathic Doctor at the Canadian College of Naturopathic Medicine.  Dr Lee practices full-time between two clinics located in Toronto and Milton Ontario and has been voted Milton’s favourite Naturopath in 2013 and 2014.   Her primary care practice focuses on family medicine, treating a wide variety of conditions such as hormonal (endocrine) disorders, fertility, digestive problems, cardiovascular disease, diabetes, insomnia and fatigue.  She has a special interest in the treatment of autoimmune diseases, paediatric and perinatal health.  Tanya offers her clinical knowledge to a number of publications, including the Natural Path.


  1. Medici M et. al Thyroid function in pregnancy: what is normal? Clin Chem. 2015 May;61(5):704-13
  2. Medenica S et. al Thyroid dysfunction and thyroid autoimmunity in euthyroid women in achieving fertility. Eur Rev Med Pharmacol Sci. 2015;19(6):977-87.
  3. National Institute of Health: Iodine Fact Sheet for Health Professionals: https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/#h8
  4. World;s Healthiest Foods: Iodine http://www.whfoods.com/genpage.php?tname=nutrient&dbid=69#foodchart
  5. National Institute of Health: Selenium Fact Sheet for Health Professionals: https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/
  6. World;s Healthiest Foods: Selenium http://www.whfoods.com/genpage.php?tname=nutrient&dbid=95#pubrecs
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