 It's crazy when you think about all the different kinds of foods we eat. We just swallow and hope it all works out for the best. Well, it turns out there are better ways to think about keeping our bodies humming healthfully along. Welcome to Nutrition Facts. I'm your host, Dr. Michael Greger. Did you know that the mighty thyroid controls your metabolism, produces hormones, and helps regulate your body temperature? What can we do to support it? Let's start with a story about plant-based milk and 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. Iodine 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 sea food 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, and sea vegetables, they can run into the same problem. Her parents reported striving to feed her only the healthiest foods. The three-year-old only got plant-based, unsalted, unprocessed foods with no vitamin supplementation, and now that could have been deadly. I mean, with no vitamin B12, those unstricted 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 partly unaware of the importance of iodine in pregnancy, just as clueless as their omnivorous counterparts. The American Thyroid Association, 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 U.S. contain this essential mineral. So in spite of the recommendations, about 40% lack it. Therefore, it's extremely important that pregnant breastfeeding women read the labels to ensure they're 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 even getting 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 carrageenan video played a role in them switching to another thickener. Hopefully, 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, which we'll cover next. Dairy milk supplies between a quarter and a half of the daily iodine requirement in the United States, though 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 like a betadine-type disinfectants, and the iodine just kind of leeches into the milk. Too bad most of the plant-based milks on the market aren't enriched with iodine, too. Fortified soy milk is probably the healthiest of the plant milks, but even if it was enriched with iodine, what about the effects of soy on thyroid function? It's funny when I searched the medical literature on soy and thyroid, this study popped up. A cost-effective way to train residents to do thyroid biopsies just stick the ultrasound probe right on top and go to town. It turns out on ultrasound, your thyroid gland looks a lot like tofu. Anyways, the idea that soy may influence thyroid function originated over eight decades ago when marked thyroid enlargement was seen in rats fed raw soybeans. Though the observation that people living in Asian countries have consumed soy foods for centuries with no perceptible thyroid toxic effects certainly suggests their safety. Bottom line, there does not seem to be a problem with people who have normal thyroid function. However, soy foods may inhibit the oral absorption of synthroid thyroid hormone replacement drugs, but so do all foods. That's why we tell patients to take it on empty stomach. But you also have to be getting enough iodine, so it may be particularly important for soy food consumers to make sure their intake of iodine is adequate. What's the best way to get iodine? For those who use table salt, make sure it's iodized. Currently only half of table salt sold contains iodine, and the salt used in processed foods is typically not iodized. Of course, ideally we shouldn't add salt at all. Dietary salt is a public health hazard. I think this title is a little over the top. Dietary salt is the number one dietary risk factor for death on the planet Earth, wiping out more than 3 million people a year. Twice as bad as not eating your vegetables. What's the best source of iodine then? Sea vegetables. You can get a little iodine here and there from a whole variety of foods, but the most concentrated source by far, with up to nearly 2,000% of your daily allowance and just a single gram, which is like the weight of a paperclip, seaweed. Given that iodine is extensively stored in a thyroid, it can be safely consumed intermittently, meaning you don't have to get it every day, which makes seaweed use in a range of foods attracting an occasional seaweed intake enough to ensure iodine sufficiency. However, some seaweed should be used with caution due to its overly high iodine content, like kelp. Too much iodine can cause hyperthyroidism, a hyperactive thyroid gland. A woman presented with a racing heartbeat, insomnia, anxiety, and weight loss thanks to taking just two tablets a day containing kelp. I noted how the average urinary iodine level of vegans was less than the ideal levels, but there was one kelp-eating vegan with a urinary concentration over 9,000. Adequate intake is when you're peeing out 100 to 199. Excessive iodine intake is when you break 300. 9,437. Way too much. The recommended average daily intake is 150 micrograms a day for non-pregnant, non-breastfeeding adults. You may want to stay below 600 on a day-to-day basis, whereas a tablespoon of kelp may contain 2,000. I'd stay away from kelp because that is too much, and stay away from hijiki because it contains too much arsenic. Here's how much of common seaweed preparation should give you an approximate daily allowance. Two nori sheets, you can literally just nibble on them as snacks like I do, a one teaspoon of dulce flakes, which you can just sprinkle on anything, one teaspoon of dried arame, which is great for like adding to soups, or one tablespoon of seaweed salad. If iodine is concentrated in marine foods, this raises the question of how early hominems living in continental areas could have met their iodine requirements. Well, here's what bonobos do, perhaps our closest relatives. During swamp visits, they all forage aquatic herbs. We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition. Good nutrition facts.org slash testimonials. We may share it on our social media to help inspire others. To see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts podcast landing page. There you'll find all the detailed information you need, plus links to all the sources we cite for each of these topics. For our timely text on the pathogens that cause pandemics, you can order the e-book out of your book or hard copy of my latest book, How to Survive a Pandemic. For recipes, check out my new How Not to Diet Cookbook. Beautifully designed with more than 100 recipes for delicious and nutritious meals. And all the proceeds I receive from the sales of all my books goes to charity. NutritionFacts.org itself is a non-profit, science-based public service where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles. Everything on the website is free. There's no ads, no corporate sponsorship. It's strictly non-commercial. I'm not selling anything. I'm just putting it up as a public service, as a labor of love, as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.