Iodine is one of the trace elements that plays a key role in thyroid function and metabolism. It’s a special concern for vegans, but it’s also one of the most common nutrient deficiencies worldwide. Somewhere between 1.5-2 billion people around the world likely have suboptimal intake, mainly due to variable soil content and lack of salt fortification. Adults need 150 mcg daily, and pregnant women need 220 mcg daily because deficiencies can lead to growth retardation and neurodevelopmental issues in the baby. In adults, deficiencies can manifest as goiter (an enlarged thyroid gland) and hypothyroidism because iodine molecules are essential parts of thyroid hormones. Interestingly, too much iodine can also increase the risk of hypothyroidism and autoimmune thyroiditis (Hashimoto’s).
Where do vegans get iodine from? The few notable vegan sources of iodine are sea vegetables (such as kombu, wakame and dulse) and iodized salt. Omnivores get it from seafood, and it’s also found in significant amounts in milk partially because iodine solutions are used as “teat dips” to clean cow’s udders. Personally I don’t want to be getting my trace elements from remnants of a cleaning solution. Unfortunately plant milks are not reliable sources of iodine and many people struggle to eat sea vegetables. If you’re not salt-sensitive and don’t have blood pressure issues, it’s worth using iodized salt: ¼ tsp provides 75 mcg iodine, half the daily recommendation for non-pregnant adults.
Processed foods, while they may be extremely high in sodium, usually don’t contain iodized salt and are not a reliable source. Sea vegetable supplements and supplements that feature “iodine from kelp” are also unreliable: ConsumerLab reports that half of the kelp supplements they tested contained twice the amount of iodine listed!
How do I test my iodine status? It’s tricky. Medscape reports that “no test can reliably diagnose iodine deficiency in individual patients.” Population-level iodine status is measured via urinary iodine, but it’s been found to be inaccurate on individual levels because values fluctuate so much with daily intake. One option is a 24-hour urine collection, but that’s cumbersome and again depends on recent intake. Because deficiencies will show up mainly as thyroid issues in adults, it’s very important to have complete thyroid labs measured yearly.
Bottom line: For my vegans, if you’re not salt-sensitive, use iodized salt and not kosher or Himalayan sea salt. If you like sea veggies, go for it, but avoid kelp. Otherwise I recommend getting iodine as part of a multivitamin/mineral as either potassium iodide or sodium iodide (aim for 100-200 mcg daily).
Source and Additional Reading: American Thyroid Association
Gropper, S. A. S., Smith, J. L., & Groff, J. L. (2009). Advanced nutrition and human metabolism. Australia: Wadsworth/Cengage Learning.