The Best Diet for Optimal Thyroid Function – Part 1

**Michael Greger** (0:00)
Doesn't it seem like when it comes to nutrition there are more opinions than facts to go around? Every day we hear new theories about diets and supplements and best foods to eat. Well, my role is to take the mystery out of good nutrition and look at the science. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger. One of the most common questions I'm asked is about a natural treatment for Hashimoto's disease, also known as autoimmune thyroiditis. The leading cause of hypothyroidism. So I did a webinar about it. Here's the whole thing on the best diet for thyroid health, as well as the healthiest natural source of iodine.
Adequate dietary iodine is required for normal thyroid function. In fact, the two thyroid hormones are named after how many iodine atoms they contain, T3 and T4. Now given that iodine is extensively stored in the thyroid gland itself, it's not something you have to get every day, but your overall diet needs to have some good source. Unfortunately, the common sources aren't particularly health-promoting. Iodized salt, dairy foods, because iodine-based cleansers like betadine are used to sanitize the udders, which results in some iodine leaching into the milk. They also add iodine to cattle feed.
Some commercial breads have iodine-containing food additives. So if you put people on a paleo-type diet and cut out dairy and table salt, they can develop an iodine deficiency, even though they double their seafood intake, which can also be a source. What about those switching to diets centered around whole plant foods? I mean, they're also cutting down on ice cream and Wonder Bread, and if they're not eating anything from the sea, seaweed, sea vegetables, they can run into the same problem.
Her parents reported striving to feed her only the healthiest foods. The 3-year-old only got plant-based, unsalted, unprocessed foods with no vitamin supplementation. Now, that could have been deadly. With no vitamin B12, those on strictly plant-based diets can develop irreversible nerve damage, but in this case, a goiter arose first due to inadequate iodine intake. Here's another case of veganism as a cause of iodine-deficient hypothyroidism in a toddler after weaning. Now, before weaning, he was fine because his mother kept taking her prenatal vitamins, which luckily contained iodine.
Most vegetarians and vegans are apparently unaware of the importance of iodine in pregnancy just as clueless as their omnivorous counterparts. The American Thyroid Association and the American Academy of Pediatrics have recommended that women even just planning on getting pregnant should ingest a daily supplement that contains 150 micrograms of iodine. Yet only 60% of prenatal vitamins marketed in the US contain this essential mineral. So in spite of the recommendations, about 40% lack it. Therefore, it's extremely important that pregnant and breastfeeding women read the labels to ensure they are receiving an adequate amount. Women of reproductive age have an average iodine level of 110, which is fine for non-pregnant individuals, but we'd really like to see at least 150 in pregnancy. It's basically a 24-hour urine test in which iodine sufficiency is defined as 100 micrograms per liter of pee in non-pregnant adults, which your average vegan fails to reach in the largest study done to date out of Boston. The recommended average daily intake is 150 micrograms a day for most people, which you can get in like a cup and a half of cow's milk. Sadly, plant-based milks are typically not fortified with iodine, averaging only about 3 micrograms per cup. In the largest systematic study to date, although many plant-based milks are fortified with calcium, they only found just 3 of 47 fortified with iodine. Of those that were, had as much as cow's milk, but those that weren't fell short.
Plant-based milk companies brag about enriching their milks with calcium and often vitamin B12, D, vitamin A, but only rarely are attempts made to match the iodine content. The only reason cow's milk has as much as it does is because they enrich the feed, or it comes dripping off their udders. So why don't plant milk companies add iodine too? I was told by a food scientist at Silk that my Karageenan video played a role in them switching to another thickener. Hopefully they'll see this video and consider adding iodine too, or some company will snatch at the market advantage opportunity.
The researchers conclude that individuals who consume plant-based milks not fortified with iodine may be at risk for iodine deficiency unless they consume alternative dietary iodine sources, the healthiest of which is sea vegetables.
OK, so to reiterate, one cause of hypothyroidism, underactive thyroid gland, is inadequate iodine intake. This is especially important for pregnant women, and women even considering pregnancy. But that largest study of vegan iodine status in Boston found most vegans have insufficient intake. So what's the best way to get it? What's the healthiest natural source of iodine? That's the name of the next video. Now, dairy milk supplies between a quarter and a half of the daily iodine requirement in the United States, so milk itself has little native iodine. The milk iodine content is mainly determined by factors like the application of iodine containing teat disinfectants. The iodine residues in milk appear to originate mainly from the contamination of the teat surface. The teats are sprayed or dipped with a betadine-type disinfectants, and the iodine just kind of leeches into the milk.