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. Dear Chris, you mentioned the 35000 men trial. Their selenium [Se] starting levels were all above 1.6 at the begining. Prof Gerhard Schrauzer ex UCSD. a lifetime Se expert told me enzymes are activated only when Se concentration is about 1.7 mcml/lt Then the numerous benefits occur! My Se plasma blood test was 1.0 mcml/lt. Then I began taking 200 mcg/d sod.selenate. At about 1.6, thats when my prostate problem fixed,still is, libido increased, finger nails grew twice as fast. Thats why the NZ recommended level is set at 1.6-1.9. That SELECT trial, confirmed Gerhard’s figures beautifully.

  2. Articles like this one drive me crazy. Should not one test selenium status before supplementing selenium?

    I have Hashimoto’s that’s subclinical hypothyroidism on the brink of needing thyroid hormone.

    Thinking that I would supplement with iodine, I followed the instructions that said supplementation with selenium was a prerequisite. I tried eating one Brazil nut a day for a few weeks and my selenium went significantly out of range!

    It took several months with no Brazil nuts to go back to where it is now: My blood selenium level is 245.00 ug/L, range 100-340.

    It seems I get plenty of selenium from the fresh, local veggies I eat (N. California farmland has lots of selenium). Can I just add iodine? I cannot find any advice anywhere about iodine supplementation when selenium is adequate.

    • if you want good iodine information, check out dr. flechas online or dr. brownstein online, both are great resources. the iodine thing is so controversial! good luck. i take it and i definitely feel better (i also have hashimoto’s.) the iodine is tricky but many docs will freak out and tell you not to take it, but flechas and brownstein agree that it’s beneficial and not dangerous.

        • To Kelly who said “That website is hardly objective. And most of their research is not peer-reviewed.” It is unclear what website you are referring to. If you are referring to one about iodine then you are dead wrong. There is abundant peer reviews on iodine’s use in medicine. Dr Guy Abraham (emeritus professor UCLA obstetrics, gynecology and endocrinology) lists his references indicating those directly involved in his “Iodine Project” research carried out in the 1990’s at http://www.optimox.com/iodine-research and there are many other doctors now working independently with iodine clinically. These doctors share and compare their clinical observations. So all their work is EXTREMELY objective – more so than their opponents. There are so many of them now you can hardly claim any truth in saying Guy Abraham is not peer reviewed.

  3. How selenium is too much and what is the amount of vitamin C that can be taken so the selenium is still effective

    • I have read that Cleveland Hospital studies recommend no higher than 2 mcg/day.. But most other studies recommend no more than 4 mcg/day because of negative side effects.
      It seems like the more i research hypothyroidism,iodine and selenium,the more confused it get…

  4. Heard in another group on FB that Chris now recommends 200 mcgs selenium only 2 or 3 times per week rather than daily. Can anyone confirm? Is that to avoid having too high levels of selenium? Thanks.

  5. Chris, I have just been ‘diagnosed’ long-distance with Hashimoto’s, by a naturopathic doctor. I trust her but I’m wondering if I should have an endocrinologist confirm the diagnosis just to have an in-person second opinion. I’m feeling a bit overwhelmed – I suspected thyroid and slow metabolism because I’ve struggled to lose weight – but I didn’t expect I would have an autoimmune disease. I just want to make sure I’m being wise going forward. Thoughts? Thanks so much!

      • A full thyroid panel will include both antibodies and more information about the different levels of thyroid hormones.

    • I’ve had the same issue saw several doctors and a naturalist on top of that I recently started going to an endrogronologist I recommend you do the same she changed me from armor to synthroid but she will be testing me every 3 months
      Good luck

      • If you suspect hypothyroidism or Hashimoto’s disease, check out Stop the Thyroid Madness website. You want to test: TSH (as it can point to more than hypothyroidism); Free T4 (this is a storage hormone that needs to convert to T3); Free T3 (this is the thyroid hormone that the cells of our body use); Reverse T3 (this is a byproduct of the T4 to T3 conversion–it will keep you hypo if it is too high); TPO and TgAb (for Hashi); TSI and TrAb (for Graves, it is possible to have both conditions). And, most importantly, get a copy of your results and it is not about being “in range”. It is about “where” in range your numbers fall.

  6. You have to supplement Iodine at the same time, otherwise you are likely creating hypothyroidism. You don’t see too many 100% studies..in a study they did in Africa(zaire I believe), when they supplemented children with cretinism with selenium they all became more hypothyroid(and the majority of normal children went hypo, while others increased). Low iodine + selenium = hyo. They also found the same effect looking at rat thyroid tissue and dosing too high of one or the other causes goiter.

    • No this doesn’t apply for those with hashimotos disease (and other causes of thyroids disorder) outside of your example (Africa, malnutrition). I have hashimotos disease, unintentionaly took iodine via another supplement that included it in ingredients, and I started to sleep less and less during the week I took it. After I was really sleep deprived from iodine intake (now causing hyperthyroid symptoms), I stopped and crashed for about a week to recover. Had to drop that semester at college thanks to iodine.

      • Because I can’t edit the above post, I meant to say “crashed for a month”. And the supplement was Attend (for ADD symptoms). apparently hypothyroid fully causes ADD symptoms, so I stopped taking stuff that would focus on those symptoms, and instead focus on lowering my thyroid antibodies.

          • Sorry I didn’t mean I was yet successful in lowering my antibodies. I’ve been taking selenium 200mcg for 1-2 months now daily, and haven’t yet checked the count. I’ve got nothing new, unfortunately, to reduce antibodies.

          • I have lowered my antibodies by 33% in five months – I follow an Auto Immune Paleolithic diet – with zero cheating or it doesn’t work. I do accupuncture, supplements, classical stretching daily, healed my leaky gut etc., and in short, I’m a new person. Top endocrinologists couldn’t fix me – I was disabled – now I feel better in some ways than I have in 30 years and continue to improve every day. We tend to think of lifestyle as minor – medicine as major when in fact it’s only lifestyle changes that cure the root cause of anything. I suggest reading Hashimotos Thyroditis The Root Cause by Izabelka Wentz.

            • I just purchased Dr. Wentz’s book along with Karen Frazier’s cookbook for Hashimotos and after less than a week I’m feeling better. As a Clinical Chemist, I find it difficult to accept selenium supplementation due to toxicity concerns but I will eat 2-3 Brazil nuts daily.

              • The issue with relying on food sources for nurtients is that it’s an inconsistent source. With farming practices it’s difficult if not impossible to accurately assess the vitamin/nutrient levels in foods.

                • I agree. Doesnt do too well if nutrients arent be absorbed properly. And who can afford tests to determine values of any nutrients in foods eaten? I am cautious with supps,vities. I do iodine (goiter) ans supp with selenium. Some is in ionic liquid form, some in unradiated raw organic brazil nuts.
                  I just dont overdo. 🙂

              • So can anyone say what we’re suppose to take in The form of Seleium Yeast? These answers are absolutely crazy. All of you are making no sense on what is right or wrong! Your stepping all over yourself switch a different answer. Where is a real site that the people know what their talking about . Seleium has been around a long time with a lot of reseaech involved. No one has said anything about the research related to depression. Anyone have any solid evidence here? What about Seleium and Krill oil or Seleium Astaxanthin ? This is the most powerful antioxidant to date. Y’all are only confusing everyone that reads your post. Get some real answerers to share or please don’t share!!!

  7. Tengo 62 años de edad y me suplementó con 200 mg de Selenio de GNC y vitamina E, casi a diario desde hace aproximadamente 3 años y tengo una salud excelente. Adicionalmente tomo vitamina B12, acido folico, 300 mg de vitamina B6, 3 gramos de vitamina C, Cloruro de Magnesio y 50 mg de zinc.

  8. I wouldn’t count on food to ensure adequate selenium. The amount of Se in Brazil nuts can vary tenfold!
    You won’t get some severe Se deficiency disease like cardiomyopathy, but will you get enough to reduce cancer risk? Questionable…..

    Read my blog…www.biafelice.wordpress.com….for more details on Se and a cursory rebuttal of the flawed SELECT study.

    In optimal health,
    Bob Iafelice, MS, RD, LD

  9. The best Selenium source I’ve found is kidney (beef or lamb). Really high levels of Selenium, so once a week is fine. No need for supplementation, plus, I also find that it’s self-limiting, because if I eat a lot it becomes slightly repulsive.

  10. Today I got my blood results for Selenium. It was 236 (Range 60-160) No wonder my hair is falling out. What can I do to lower this besides stop supplementing with the 200mg I was taking a day?

    Thanks Chris!

  11. What form of selenium was in those studies? Isn’t there a form that’s toxic (sodium selenite/selenate) and chelated forms that are not?

    Could that be a factor in the findings?

    • @rawdawg

      Yes, i make the same point above. We know that not all supplements are equal. Some are natural, non toxic, and effective, while others are unnatural, toxic, and harmful.

      Chris, why did you not emphasize this from the studies referenced? It makes all the difference. It could mean the studies are not very meaningful if an unnatural form was used – which I suspect is the case. The studies would then only imply dont use an unnatural form of selenium and vitamin E, which we already know is bad. These studies are likely useless for this whole discussion.

  12. I take 100 mg of selenium when I eat fish as our functional med MD said it helps bind mercury in the gut. I also have Hashimoto’s and get about 50 mg in a multi he has me taking. Does selenium help us get rid of mercury? Is taking 100 mg only when you eat fish maybe 1-2x week safe?

    • Laurie, you probably mean 50 and 100 *mcg* selenium, since 50 or 100 mg would be a massive overdose. Most people could tolerate the amounts you mention, but some such as myself would not.

  13. This was great, thanks for sharing! This seems to be the case for many micronutrients, especially those involved in oxidation/antioxidant (vitamin E, beta-carotene). It usually boils down to whole foods being the better option. I wonder where this breaks down though. What do you think the effects would be of eating a dose of brazil nuts daily in a population with a high baseline selenium status? I suppose their high selenium status would be due to a diet already high in selenium (or is there a biological component?). Does the selenium in a whole food matrix protect against the negative effects of the high selenium dose?

  14. How do you get your selenium levels tested? My local lab doesn’t do toenail testing. Is it through hair analysis, blood, urine?? Many thanks!

  15. I would like to know in the studies referenced about selenium and vitamin e supplementation increasing the risk of prostate cancer, what types of selenium and vitamin e were used (the summary referenced does not say)? It makes a HUGE difference. I strongly suspect the types that were supplemented with were synthetic unnatural toxic forms, not whole food based natural forms. Selenium in the form of selenomethionine is not a good form to supplement with and vitamin E as dl-alpha tocopherol is a toxic poison made from coal tar – it is NOT natural. It belongs in the trash. It is often the case in these studies that the researchers have no clue what they are talking about and publish studies making generalizations that are completely wrong. I suspect that is the case with these studies because in general conventional doctors are clueless when it comes to nutrition.

    I am very surprised and disappointed that Chris did not bring up this fact. For example there was a study that came out pretty recently that claimed vitamin E supplementation increased risk of prostate cancer (see http://www.drhansen.com/2011/10/16/vitamin-e-study-more-biased-science-exaggerated-headlines/). The type of vitamin E used in the study was dl-alpha tocopherol – a toxic unnatural form that no one should supplement with. It is derived from coal tar, not food. Unlike d-alpha-tocopherol.

    The book “The Life Bridge” discusses for example the difference between selenomethionine and organic yeast bound selenium. There is a HUGE difference. HUGE. Selenomethionine has almost no antioxidant activity whereas yeast bound has profound antioxidant activity. Also there are 8 forms of vitamin E, 4 tocopherols and 4 tocotrienols, not just one form. Ignorant researchers do not bring this up sometimes (maybe because they just dont know) and make grossly wrong generalizations. I seriously doubt tocotrienols were used in any of these studies, although they are the most biologically active forms of vitamin E.

    The point is that the form supplemented with MUST be taken into account. Of course too much selenium or vitamin e in any form is not healthy. But if you are going to supplement, use a natural whole food organically bound form. It not only will actually work for you but it will not be toxic and cause harm.

    Selenium, in the whole food form, is considered by many cancer experts the number one protocol to prevent cancer in general. This is important to keep in mind and low selenium can cause all kinds of physiological problems. It is most concentrated in the liver, kidneys, and thyroid and is vitally important for the proper function of all three. A deficiency will cause liver malfunction, kidney malfunction, and thyroid malfunction. Selenium is the most important nutrient for the activation and function of glutathione peroxidase, a very important antioxidant. It also directly affects gene expression and thus even a slight deficiency in selenium can have devastating effects in the long term. Selenium is also very effective for protecting against mercury poisoning because selenium binds to mercury. In other words selenium sufficiency is incredibly important to health.

    • Yes, you are right about the vitamin E! Alpha tocopherol is probably the cheapest & is therefore used in most studies & hence the lack of benefits.

  16. Excellent post, as usual! As a Functional Medicine specialist we usually measure Se levels if we are planning long term supplementation. I practice in India, where few studies from Northern India have shown excess Se in the soil. While it is ok to supplement with small quantities of Se, higher doese & long term term use would mandate measuring in the patient. ( Similar to iodine supplementation).

    • Why not just keep an eye out for actual Se toxicity symptoms (such as the nails) as they are all reversible in time anyway. I question how much test results prove. What’s the documentation of their evidential value? And even if you get a test result on day x, a week later the result could be different anyway. One thing that’s guaranteed is you have to spend money and time on them.

  17. Chris,

    What are your thoughts about the genotoxic and carcinogenic aflatoxins present in brazil nuts? I decided against eating brazil nuts regularly for the selenium after learning that brazil nuts are susceptible to aflatoxin contamination, produced by Aspergillus nomius and Aspergillus flavus fungi present on the nut. Eating brazil nuts regularly could result in chronic toxicity of aflatoxin, which can cause cancer.

  18. I believe Chris has written about Low Dose Naltrexone for Hashi’s in the past. There’s a large group of over 4,000 members in the Beating Thyroid Disease with Low Dose Nalxtrexone group (https://www.facebook.com/groups/LDNthyroid/.) For anyone with Hashi’s, LDN can be highly beneficial. You must learn how to dose properly and the folks there can provide some very useful advice.

    Also, you might want to take additional taurine and see how it goes.


    Though I’m no thyroid expert, this information may help someone: My friend who had gone hypo after eating way to much soy and raw brocolli, among other goitrogenic foods, and went all “health” nuts and stopped any iodized salt. To reset herself, besides changing her diet, she walked min. 5,000-8,000 steps a day. 10,000 steps per day would be ideal.

    There’s a lot of chatter on the benefits of coconut oil and hypothyroidism. http://wellnessmama.com/36/thyroid-problems-and-coconut-oil/ Mercola has some articles too. I like it because my brain is un-fogged.

  19. Did the studies measure Iodine status? Could this be a ratio problem instead of a single nutrient issue? For example Chris Masterjohn has done a great job explaining the interaction of A, D & K2. Paul Jaminet recommends taking selenium with iodine. I would love it if someone could crunch the data from the study and figure out if Iodine deficiency explains the results.