A streamlined stack of supplements designed to meet your most critical needs - Adapt Naturals is now live. Learn more

Important Update on Selenium Supplementation


Last updated on

selenium dosage, best form of selenium
Standard selenium dosage when you're deficient, is important for overall health.

A while back I wrote an article on the role of selenium in autoimmune thyroid disease.

I summarized several studies, which found that selenium supplementation reduced inflammation and damage to thyroid tissue, lowered thyroid antibody levels in the blood, and improved the conversion of T4 to T3.

However, I also sounded a note of caution when it comes to selenium supplementation:

“These preliminary studies show the positive effects of selenium supplementation on inflammatory activity in autoimmune thyroid conditions, but the long-term effects of supplementation on thyroid health are still unknown. And we know that selenium is an essential component of the enzymes that convert T4 to T3, but whether supplementation will increase serum T3 levels is unclear.

While it seems that selenium supplementation would be an obvious solution to poor thyroid function, long-term consumption of high doses of selenium can lead to complications such as gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage. (1) Additionally, supplementing with selenium in the context of low iodine status may actually aggravate hypothyroidism. Mario Renato Iwakura discusses this particular topic extensively on Paul Jaminet’s Perfect Health Diet blog.

For now, the best option for most people may be to include selenium-rich foods in the context of a healthy Paleo diet.”

A study published last year—which I just came across a few weeks ago—appears to validate this caution, at least for middle-aged men. (2) It was a large clinical trial (with over 35,000 participants) that examined the relationship between baseline selenium status, supplementation with selenium and vitamin E (either together or separately), and future rates of prostate cancer in men over 55 years of age.

Here’s what the researchers found:

  • Baseline selenium status alone was not associated with prostate cancer risk.
  • In men with high baseline toenail selenium (>60th percentile), selenium supplementation of 200 mcg/d increased the risk of high-grade prostate cancer by 62% when taken alone, and by 224% when taken with vitamin E.
  • In men with normal or low baseline toenail selenium (<60th percentile), selenium supplementation of 200 mcg/d (either alone or with vitamin E) did not substantially increase or decrease the risk of prostate cancer.

It’s worth pointing out that these findings contradict two previous (and considerably smaller) observational studies in the United States, which found that low toenail selenium status increases the risk of prostate cancer. (3, 4) In addition, a large Dutch study including over 58,000 participants found that those with the highest toenail selenium status had a 37% lower risk of prostate cancer than those with the lowest selenium status. (5)

Like what you’re reading? Get my free newsletter, recipes, eBooks, product recommendations, and more!

Should you be supplementing with selenium? Find out what @ChrisKresser has to say.

However, in the United States, selenium levels are typically much higher than they are in Holland, where deficiency is widespread. While it’s entirely possible that the very low selenium levels seen in Holland are associated with increased prostate cancer risk, there does not appear to be a correlation between selenium and prostate cancer in the United States—at least within the ranges of toenail selenium found in U.S. men over 55 years of age.

So what are we to make of this?

A growing body of research suggests that the effects of micronutrient supplementation are dependent upon the status of that nutrient in the target population. (6) If baseline levels of a particular nutrient are low, supplementation may lead to improved outcomes.

But if baseline levels are normal or high, supplementation may cause harm—as it appears to have done in this study. This shouldn’t be too much of a surprise; most nutrients have a “U-shaped curve”, which means that both too little and too much can cause problems.

On the other hand, several studies indicate that supplementing with selenium has several benefits for people with autoimmune thyroid disease, including reduced inflammation and damage to thyroid tissue. At least one study found that selenium supplementation produced these benefits even when selenium levels were normal at baseline. (7) Since both Hashimoto’s and Graves’ disease are associated with increased morbidity and mortality, an intervention that reduces the autoimmune/inflammatory burden in these conditions might be expected to reduce morbidity and mortality.

There’s little doubt that maintaining adequate selenium levels is important to immune and thyroid function. But given the potential long-term risk of supplementation, I think the best option for most people is to meet their need for selenium by eating selenium-rich foods. Great sources include: brazil nuts, crimini mushrooms, cod, shrimp, tuna, halibut, salmon, scallops, chicken, eggs, shiitake mushrooms, lamb, and turkey. Brazil nuts are a particularly rich source; just 2–3 a day will provide roughly 200 mcg of selenium, which is the amount used in many of the autoimmune thyroid studies.

Finally, while this study was focused on prostate cancer risk in men over 55, it’s probably prudent to assume that long-term selenium supplementation in both younger men and women of any age may also have undesirable effects.

I will, of course, continue to keep an eye on the research in this area and report back if any new findings come to light that would change my recommendation.

ADAPT Naturals logo

Better supplementation. Fewer supplements.

Close the nutrient gap to feel and perform your best. 

A daily stack of supplements designed to meet your most critical needs.

Chris Kresser in kitchen
Affiliate Disclosure
This website contains affiliate links, which means Chris may receive a percentage of any product or service you purchase using the links in the articles or advertisements. You will pay the same price for all products and services, and your purchase helps support Chris‘s ongoing research and work. Thanks for your support!


Join the conversation

  1. How much selenium is recommended for women? I live in New Zealand and the soil here is deficient in selenium.

  2. My do had me start 200mg of selenium back in Oct. There was 100 in my multi and then I take additional 100. After reading this should I think I will just take my multivitamin. These supplements drive me crazy. My antibodies were a little high when he tested. I have problems with pressure uticaria which is obviously caused by some underlying inflamation. Haven’t gone paleo but am gluten free. I wish I could see you Kris. You are so knowledgeable on thyroid.

  3. The study that showed increased risk of high grade prostate cancer, did it use selenamethionine? That could be the problem with supplementation in that case. Not all selenium supplements are created equally. I actually think selenium supplementation with methylselenocysteine is safer than Brazil nuts, which contain their selenium in the selenomethionine form (as I understand it)

  4. The importance of selenium in fighting colon also should not be overlooked. Definitely not something you want to be low in.

      • Selenium is one means to an end – thyroid nutrition and thyroid optimization – which in turn decrease cancer risk. Thyroid has a lot to do with proper cell differentiation, which is impaired in cancer. So an optimized thyroid and proper cell differentiation are the goals, not trying to ward off cancer with selenium. Individual selenium needs and tolerance vary widely.

  5. It is often recommended that Hashi patients keep their iodine levels low to avoid aggravating the autoimmune process and via low-iodine diet and avoiding supplemental iodine. In this scenario, supplementing with selenium would likely tilt the balance in the direction of selenium excess, would you agree? If selenium were obtained through diet alone, how often would dietary sources need to be consumed, daily? several times/week? Thank You.

  6. I have been taking Selenium supplements since 2005 when I was diagnosed with Hashimotos. My TPO anti-bodies have remained static throughout at around 900. Could be malabsorption due to Crohns…. I take 200mcg daily on an empty stomach ! Haven’t seen Brazil nuts here in Greece !

  7. It’s good to get these updates.
    My understanding is that the upper limit for selenium (RDA) is 400 mcg/d. So if you are taking a supplement of selenium of 200 mcg/d (to counterbalance iodine supplements from seaweed), would you need to be concerned about getting too much selenium?

    I would rather get the selenium I need from food sources too but have major digestive problems.

    Brazil nuts that I’ve been able to purchase all taste/smell rancid. Plus I don’t digest nuts well. Yes there are lots of other food sources of selenium. Just that I’m trying to help my Hypo thyroid using fucus seaweed for the iodine (and other minerals and trace elements). Taking the selenium supplement based on your articles about here about the protective feature of selenium for increased iodine consumption.

    In the article about it was stated: “selenium supplementation of 200 mcg/d increased the risk of high-grade prostate cancer”…..therefore it may not be so good to take supplemental selenium in the long term. So why is taking a supplement of 200mcg of selenium not so good, yet eating 1-3 brazil nuts (about 200mcg of selenium) is recommended instead? (the amount of selenium being about the same)

    • You might like to try Wilderness Family Naturals’ soaked and dehydrated Brazil nuts to see if they seem better to you than the ones from your other sources.

  8. I think the amount of selenium in Brazil nuts is related to how selenium-rich the soil was that the nuts were grown in. My understanding is that Brazil nuts can be a good source of selenium, but they are not guaranteed to be, depending on their source.

    • Yes, soil composition is critical, but if all other variables are equal, brazil nut have far-and-away the most selenium, you just need 2 or 3 nuts a day. I think of them as giant chewable tasty selenium supplements.

      • Brazil nuts are the second largest export from Peru/Brazil based on nut and seed, agricultural export The jungle soil is rich in selenium. The Brazil nut trees are NOT cultivated crops because it takes as long as 30 years to produce their first seed pods. These pods are the size of grapefruit and contain 12 to 25 nuts with their own hard coating/shell. The fruiting trees are very tall, 100 to 130 feet and can fruit for 300 years or more. No soil additives, no pesticides are used and harvesting is very difficult and dangerous work. Just take a look on Google what these monster trees look like. I’ve live in Peru for the better part of 30 years and there is not going to be a wide range of difference in selenium found in Brazil nuts from Peru or Brazil because there is a limited number of social groups that go into the jungle and harvest them It is not done by large corporations, although some large corporations do end up purchasing, pack, transport and export these nuts across the globe.

  9. I’m glad to read this article, because I wanted to start to take selenium supplementation. I bought 2 different types of supplementation bit somehow I didnt feel to take them. Finally I went back to the store and changed them to organic brazil nuts. Funny that I did it because I read the study a few days ago, and I thought that natural source would be better 🙂
    Chris thank you very much for verify that my decision was right 🙂
    Unfortunately my Anti TPO still high, although Im gluten-free for a year now. In Hungary where I live, most peope take medication for Hashi, and I pioneer here trying to solve the problem by dietary changes.
    Hopefully I will be the first healed person in Hungary! 🙂

    • You can get a food sensitivity test done, since you are already gluten-free. Are you 100% GF?
      As a physician i’d be concerned if my patient is not on Thyroid medication with abnormal Thyroid function reports & still high Thy antibodies. Do you have compounding pharmacies in Hungary? I recommend compounded T3-T4 combinations for my patients.No porcine thyroid for people with Thy antibodies. PLEASE do not take my recommendation as medical advise. “Curbside consults” can be dangerous & i dont normally do it 🙂

  10. Actually *one* brazil nut is quite adequate for the task of selenium supplementation for nutritional purposes. Most people are going to get their daily requirement of selenium 70 mcg by eating nearly any kind of diet, which you can prove to yourself by googling selenium content in foods and calculating selenium in a wide range of diets.

    Any mineral is going to be toxic in excess. What amounts to excess can vary somewhat with the individual.

    Some Hashi patients claim to be helped by selenium, others such as myself can be horribly aggravated by it. Some percentage of T3 is produced in the thyroid itself, the remainder is produced “peripherally” or in other parts of the body especially the liver. But in Hashi, when you stimulate the thyroid to “produce” with thyroid precursor nutrients and other thyroid stimulating substances such as ashwagandha or spirulina, antibodies can come out of the woodwork so to speak to attack the thyroid, producing inflammation, whereas antibodies don’t attack circulating thyroid from thyroid meds. I speculate that whether a Hashi patient is helped or aggravated by selenium supps may depend on how dead the thyroid is, what percentage of T3 is produced at the site of the thyroid vs. peripherally, and on constitutional types and genetics.

  11. Maybe there is a difference in response between persons having an inflammatory condition and healthy persons? In the study I link to below healthy men were fed a diet with 300 mcg selenium per day for 120 days and the end of the study their blood work indicated slight HYPOthyroidism, and in addition their sperm motility decreased (which is the main topic of the study. So even if it might be beneficial to supplement with higher doses of selenium for certain diseases, it might be wiser for healthy people to stick with the RDI recommendation of 50 mcg. However, the study is rather small, only 11 persons, so I don’t know how strong evidence that is. That’s your thoughts, Chris?

  12. Would cycling the selenium dosage be of benefit? Maybe 3 weeks on 1 off? As I understand it the amount of selenium can vary, not just by country or regions but even within a farm field itself. That Brazil nuts within a few hundred feet can have almost none to 200mcg per handful.

    • Yeah, this is why it’s unreliable to depend on Brazil nuts as a consistent source of selenium. You can try 3 a day as Chris suggests but test to make sure you’re getting enough!

  13. Brazil nut trees do no require selenium to grow. So, how can I tell if the Brazil nuts I am eating have any selenium in them? Oh, right, it’s on the package label.

    If there’s no selenium in the soil where the trees are grown, there is no selenium in the nuts. Otherwise, where would the nuts get the selenium?

      • Selenium is an inorganic mineral, not a vitamin.

        Perhaps you meant “vitamins and minerals,” but minerals are chemically quite different from vitamins.

        And, if I’m correct, they’re generally elemental and not something which the bodies of plants or animals can synthesize from other materials.

        Vitamins are complex structures generally consisting of many elements – carbon, hydrogen, oxygen, nitrogen, etc. – which are common in food and air.

        • In otherwords, the element comprising the mineral must be directly ingested, or absorbed through the skin, or what-have-you, to be within a living creature such as a plant.

        • You are correct. Minerals are “elemental” and cannot be manufactured via any biological process. Selenium is an element.

      • Except selenium is a mineral/element that gets created inside a star/sun. There is a finite amount of it here on earth and no plant or organism can create it only utilize it.

  14. I have given up on Brazil nuts as they very high in PUFAs.
    They always tasted of fungus (even the organics from Whole Foods).
    I’ll try my luck with seafood and the other foods mentioned.

  15. I tried going the Brazil nut route but unfortunately Brazil nuts are loaded with mold. Also, for many people with poor digestion, the nuts won’t be broken down adequately to absorb the selenium. I wasn’t able to get my selenium levels to normal with Brazil nuts (tested several times) until I supplemented. Something to consider.

    • Thank you for your input. I do a brief soak in hydrogen peroxide before the long soak for my brazil nuts, but I still notice that I don’t enjoy them like the other nuts and seeds that I also ate. Walnuts, pecans, almonds, sunflower all came out crunchy and delicious after dehydration. Brazil nuts continue to suck probably due to rancidity and ‘maybe’ molds. In any event, after reading the feedback, I’m going to abandon brazil nuts once I’m finished with what I have and go on with natural selenium supplement.

  16. Interesting! I was never that worried about selenium… I was told that grass fed Alberta beef was a good source… so I’m glad to hear that’s likely correct. And I eat brazil nuts sometimes anyway, heh. 🙂

  17. Well, this explains the recommendation you made for me yesterday. I prefer getting selenium from food anyway. Thanks, Chris!

    • It appears that phytate does not inhibit selenium absorption—at least not according to this study in baby chicks.

      This study shows that Brazil nut consumption improves selenium status (presumably without soaking them; there is no mention of that in the study and I think it unlikely the participants did it on their own without instruction).

      This study found a similar result. A single consumption of large amounts of Brazil nuts improved selenium levels and lipid profiles of healthy volunteers.

      • Since you are hard to reach, I figured I’d post here:

        Regarding Phytic Acid:

        A diet rich in vitamin C and carotenoids — which kale, brocolli, tomatoes, whole fruits, yams, carrots, peppers have in abundance — studies show that eating foods rich in these nutrients prevent the inhibitory effect of phytic acid on iron absorption. It’s HIGHLY likely other nutrients as well are getting absorbed just fine too. It appears that phytic acid is an anti-nutrient in diets low in vegetables and whole fruits. Sugar’s horrible effects on gut microbes doesn’t help either.

        I found the information about phytic acid on Weston A. Price’s site in an article “Living with Phytic Acid” way, way, way, way down on the page. This, of course, doesn’t mean that preparing your beans and seeds by soaking them, sprouting, fermentation is not beneficial, but in the context of a diet rich in the supporting nutrition, it’s not that big a deal.

        Off topic, but regarding RAE to A conversion which you might find interesting. The ability to convert RAE to Vitamin A varies from individual to individual. Some people are excellent at it and some people are not. Adding fat to a meal greatly increases absorption. Besides the fat, so one can get more carotenoids to work with, the RAE to A conversion requires bile acids, iron, riboflavin, niacin, and zinc. Bile acids are affected by many factors, one is fructose sans whole fruit. So many people, vegans included obviously, fail to get the supporting nutrition in their foods and also have a very sugary lifestyle.

        I’m an avid reader of your work, Westion A. Price, Chris Masterjohn, and other nutritional information outside of my vegan diet — my personal one. I’ve casually studied failed vegans. Their go to food after ending that diet is predominately fish, fatty fish. I observed Pacific Northwest vegans who were thin (too thin in my opinion), tired, poor teeth, brain fogged, dry skin, and so forth, however the vegans in Florida are rather healthy. Fat + sunshine and absorption and conversion are dramatically increased in a lifestyle that is fairly active and doesn’t not indulge in too much sugar.

        I’ve noticed that the vegans who are healthy after decades doing this, were not the ethically, environmentally, or health motivated ones, they are the ones with greater empathy for animals. I’ve noticed the “in-your-face” ones on an ideologically soap box fail more often, which I refer to as the “spiritual foot in your mouth” or “the universe doen’t appreciate rigidity” syndrome. The Tao flows.





        Iron absoprtion in man: ascrobic acid and dose-depended inhibition. American Journal of Clinical Nutrition. Jan 1989. 49(1):140-144.

        Rice and iron absorption in man. European Journal of Clinical Nutrition. July 1990. 44(7):489-497.

        Layrisse M and others. New property of vitamin A and Bcarotene on human iron absorption: effect on phytate and polyphenols as inhibitors of iron absorption. Archivos Latinoamericanos de Nutricion Sept 2000 50(3).

      • hello chris
        this is maryum,i have TSH levels high 7.5,uIU/ml,i am a female of 37 yrs almost ,my gut also weak,i pass WBCS in urine ,have recurrent UTI,i also have clots during monthly periods.my LDL increased,please help and which medicines should i use,plz contact me on my email.

    • Ben, can you provide any information on your source that Brazil nuts can’t be soaked? Incidentally, Wilderness Family Naturals sells organic Brazil nuts that have been soaked and dehydrated at low temperatures and they are delicious. They recommend refrigeration.

      • Yes, me too! I soak them ~24 hours, dumping the water half-way through. and then dehydrate on low temp for ~24 hours. Fantastically sweet.