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Selenium is a mineral needed in trace amounts for optimal health. It is a key nutrient for a robust immune system, a youthful appearance, and a sharp mind. It is also an essential nutrient in the fight against cancer. Two (Selenium-rich) Brazil nuts a day keeps the doctor away!

Selenium is not what your doctor would usually test, even though it can tell you a lot about your health. However, you can request it from your doctor and plug your test results into Lab Test Analyzer. You will find all the information you need about your selenium values, such as if your levels are optimal. And if they are not, it will tell you how to get there, using evidence-based lifestyle, diet, and supplement tips.

Introduction: What is Selenium

Selenium (Se) is a mineral that exists in poultry, fish, cereal, and eggs. It was considered a toxin until 1957; however, current research shows eating proper amounts of Selenium has many apparent health benefits [R].

Plants take in Selenium from soil; thus, people around the world eat different daily amounts of Selenium depending on the concentration of the mineral in the surrounding geography. Therefore, depending on geography, individuals may suffer from Selenium deficiency [R].

Current scientific research is looking at redefining the recommended values of Selenium.

The Selenium That I Recommend

Selenium Snapshot

  • Longevity7.0/10
  • Inflammation7.0/10
  • Mood6.0/10
  • Cognition5.5/10
  • Energy9.6/10


  • Fights inflammation and improves the immune response.
  • Vital for healthy thyroid function.
  • Helps the body fight cancer.
  • Can reset the Circadian rhythm.
  • Increases wakefulness


  • May contribute to Type II Diabetes when taken in excess.
  • May lower active thyroid hormone in men.
  • More is not necessarily better with this supplement.  You want to supplement moderately.

Benefits of Selenium

There exists a breadth of research on the health benefits of Selenium — from mood to cancer. Moreover, Selenium deficiency is linked to many negative health complications [R].

1) Selenium Fights Inflammation

Selenium inhibits NF-kB and its activation of interleukin-6 and TNF-alpha production, according to a review study [R].

Selenium may decrease abnormally high levels of IL-8 and TNF-alpha [R].

2) Selenium Helps Regulate the Circadian Rhythm

Selenium helps restore a disrupted circadian rhythm [R].

3) Selenium Has Anti-Aging Properties

Research has long attributed the benefits of fish consumption to polyunsaturated fatty acids; however, the benefits of fish consumption may also be due to the increased Selenium consumption.

Selenium works with the fatty acids to support cognition and prevents the polyunsaturated fatty acids from forming undesirable products.

In a recent study (Prospective cohort), elderly participants (over 69) that had the highest fish consumption and subsequently the highest levels of Selenium and polyunsaturated fatty acids had the best cognitive function [R].

There also exists a correlation between low Selenium status and cognitive decline [R].

In one study, individuals with Alzheimer’s had 60% of the Selenium concentration of those in the control group [R].

4) Selenium is Important for Thyroid Function

When the body is deficient in Selenium, it is the thyroid and brain tissues that concentrate the remaining supply.

The thyroid has the highest selenium content per gram of tissue [R].

In patients with Hashimoto’s Thyroiditis, Selenium supplementation reduced thyroid peroxidase (TPO) antibodies significantly compared to a placebo [R].

In a mouse model of autoimmune thyroiditis, Selenium increased T-reg cells and lowered blood levels of thyroglobulin antibody (TgAb).

Also in patients with Hashimoto’s and in pregnant women with anti-TPO antibodies, supplementing with Selenium decreased antibody levels and improved the structure of the thyroid gland as seen through ultrasound.

Those with Graves disease also saw remission more quickly through Selenium supplementation.

In women with low iodine, the lower the blood levels of Selenium, the higher the thyroid volume, a risk of goiter, and risk of thyroid tissue damage [R].

5) Selenium May Help Prevent Cancer

Selenium may help prevent cancer in a multitude of ways. Increased but not toxic levels of Selenium are shown to lessen the risk of colorectal, prostate and lung cancer. Selenium is capable of breaking down cancer cells as well as stopping the cell cycle.

Although there are links between Selenium intake and cancer prevention, the genetics, gender, and age of the patients, along with the stage and type of cancer, affect Selenium’s preventative effectiveness [R].

In America, individuals consume enough Selenium, according to current research, which should decrease the likelihood of cancer.

A longitudinal study found that over an eight to ten year period, Selenium reduces the risk of dying in individuals who suffered from lung [R], colorectal and prostate cancer [R].

In another study, Selenium decreased the risk of dying in individuals with skin cancer [R].

Those who were given Selenium compared to placebo in the study had a 50% lower cancer mortality in non-melanoma cancer.

A combination of Milk thistle (Silymarin) and Selenium significantly reduced LDL and total cholesterol in men after they removed their prostate. These markers are risk factors for prostate cancer progression [R].

6) Selenium Helps Immune Defense (especially against viruses)

Lack of Selenium can cause the body to commit an abnormal immune response. Increased Selenium intake allows for the destruction of tumor cells and also aids the body in producing antibodies.

Selenium deficiency is also linked to disease progression in viral infections. In Selenium deficient individuals, harmless viruses can become dangerous. As a result, Selenium deficiency can lead to cardiomyopathy, which makes it hard for the heart to deliver blood to the rest of the body [R].

With sufficient Selenium levels, cellular immunity will be strong and cells will be less likely to die or be damaged.

Having less than ideal Selenium levels causes stress on cells and their cell death activates the virus and allows for the virus to replicate at faster rates.

Selenium also helps fight against HIV by inhibiting the replication of the virus [R].

An individual’s Selenium status can be a predictor of their disease outcome: Patients who are Selenium deficient are almost 20 times more likely to die from HIV related causes than those who have normal values of Selenium.

In children, low values of Selenium not only increase the likelihood of death from HIV, but the disease also spreads faster [R].

7) Selenium is Good for Th2 Dominant People

Selenium supplementation may also help divert immune responses away from the Th2 type associated with allergies and asthma and promote the Th1 type, providing protection against viral infections and cancer [R].

8) Selenium Aids Fertility and Reproductive Health

In animals, Selenium deficiency is correlated with an increased likelihood of miscarriages: females who suffered the first-trimester miscarriage were more likely to have low Selenium levels [R].

Selenium also affects male fertility as Selenium is necessary for the formation and development of sperm [R].

When sub-fertile men were given Selenium supplements for three months, they significantly increased their sperm motility [R].

Selenium is important for synthesizing testosterone in rats [R], but it doesn’t increase testosterone if people aren’t deficient in it [R].

9) Selenium Improves Mood

Selenium affects the cells of the nervous system, and, thus, affects mood. Neurotransmitters do not turn over as quickly in Selenium deficient individuals.

Low Selenium levels are correlated with depression, anxiety, confusion, and hostility. Supplementing for 5 weeks with 100 mcg of Selenium, lessened anxiety among patients who participated in a clinical trial [R].

Hospitalized elderly, cancer, and/or HIV patients reported less anxiety after Selenium was added to their diets [R].

10) Selenium Increases IGF-1

An Italian study of adults aged 65 and older found a positive and significant association between selenium and IGF-1 [R].

If you’re confused by all this information, Lab Test Analyzer is your digital health advisor that helps you understand your lab tests and makes recommendations based on your results.

Drawbacks of Selenium

There exists much evidence to support the health benefits of Selenium; however, Selenium in excess can be dangerous to an individual’s health.

Excess Selenium May Promote Type II Diabetes

Type II diabetes and increased blood sugar are positively correlated with Selenium. Even when factors of gender, weight, and age were controlled for, there existed a correlation between high selenium levels and type II diabetes [R].

However, the relationship between diabetes and Selenium is not simple. Women who suffer from diabetes during pregnancy have lower Selenium concentrations than pregnant women [R].

The mixed results surrounding Selenium and diabetes underscores the fact that excess Selenium, not simply Selenium, promotes diabetes.

Excess Selenium May Lower Active Thyroid Hormone (T3) in Men

Too much Selenium (300 mcg) lowered T3 in men in one study [R], but a larger study couldn’t replicate the results [R].

Excess Selenium may increase the risk of prostate cancer mortality

Selenium supplementation of 140 or more μg/day after the diagnosis of non-metastatic prostate cancer may increase the risk of prostate cancer mortality [R].

Selenium Toxicity

The Tolerable Upper Intake Level (UL) for Selenium is 400 mcg per day for adults [R].

Some immediate indications of Selenium overdose include digestive and neurological symptoms (including tremors), light-headedness, facial flushing, sore muscles, and difficulty breathing. Some more severe reactions include a heart attack, heart failure, kidney failure, and, very rarely, death.

Curcumin is protective against selenium toxicity in the liver and kidneys [R].

A 2015 review study of lab and population results found that Selenium may be harmful in doses smaller than originally thought [R].

In fact, randomized trials put Selenium’s protective abilities under scrutiny, finding that it did not protect against cancer and other chronic diseases, but rather increased the risk for prostate cancer and skin cancer, in addition to type 2 diabetes [R].

Sources of Selenium 

Selenium exists naturally in a variety of foods, but it can also be purchased as a supplement.

This nutrient can be found in nuts (especially Brazil nuts), lamb, fish, poultry, cereal, and eggs.

Fish is especially a good means of consuming Selenium because Selenium helps your body process the omega 3’s and iodine, which are also beneficial to health.


I recommend 150-250 mcg from all sources daily. (RDA is 55 mcg). You could take 100 micrograms (mcg) Selenium or a Brazil nut.

I take 100 mcg per day in supplemental form for the long term.

Individuals should take in at least 40 mcg to avoid becoming deficient [R].

Eating 2 Brazil nuts a day is as effective as 100 micrograms of Selenium for increasing selenium status [R].

Selenium on SelfDecode

Irregular Selenium Levels?

If you have not yet tested your selenium levels, I recommend that you ask your doctor to do it. If you already have your blood test results and you’re not sure what to make of them, you need to check out Lab Test Analyzer. It does all the heavy lifting for you. No need to do thousands of hours of research on what to make of your various blood tests.

People don’t realize that their blood test results contain a gold mine of information that’s waiting to be unearthed. Unfortunately, not everyone has the time or the inclination to sift through dozens of research papers.

It’s super-simple so that even if you don’t have any background in science, you will understand what your results mean and what you can do to get them in the optimal range.

Lab Test Analyzer gives you up-to-date scientific information about your lab results. In addition, you will get both lifestyle tips and natural solutions to help you optimize your health. You can also rely on our science-based Optimal Ranges to prevent potential health issues and maximize your overall well-being.

All of the content is backed by science and researched by a team of PhDs, professors, and scientists.

We’re all unique, so we deserve solutions that treat us that way.

Buy Selenium Supplements

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The information on this website has not been evaluated by the Food & Drug Administration or any other medical body. We do not aim to diagnose, treat, cure or prevent any illness or disease. Information is shared for educational purposes only. You must consult your doctor before acting on any content on this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.


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  • Penelope

    I’ve been sleeping 8 hours plus with 100mcg of selenium a day. Before I was only sleeping 90 minutes at a time and awake for hours. I’m blown away by this change. It sure did reset my circadian clock.

    1. Shea

      Glad it has helped, Penelope!

  • May

    Patrice, I hope you’ve talked with your dr. Diabetes is more complex than getting answers from the net. I wish you good health. May*

  • May

    After watching “Calling Dr Pol” I realized that selenium helps newborn animals build leg muscles. I have neuropathy, and the physical therapy made my legs so weak that I could barely walk away from an appt. Since using 200mcg daily, my legs feel better and I can do my exercises.

  • patrice

    so if i have diabetes can i take selenium

    1. Nattha Wannissorn, PhD

      I don’t see why not but talk to your doctor.

  • Peter Beerden

    Attention! Do not rely on Brazil nuts for your selenium. They do not need it to grow, they only happen to absorb a lot of selenium if they are grown on seleniumrich soil. Many of the Brazil nuts on the market will contain little selenium or none at all….

    1. kevin

      Brazil nuts make selenium without the seniumrich soil!

    2. Rose Pieron

      I have graves disease and lost about half my hair, I started taking 100 mg of selenium a day, my hair stopped falling out and now growing back plus I have eyebrows now

  • Keepitup

    Selenium sources are just as important as the supplement itself. Organic high-selenium yeast has proven over and over in clinical trials to have all the health benefits and other selenium sources cannot replicate the results. As for all good products there are crappy and ineffective ones. Do your research, get a pharmaceutical-grade quality instead of wasting your money at Walmart and GNC. Selenoprecise selenium fixed my inflamed, bum knee and brought it back to normal. As an added bonus, my hair thickened back up and I now take it daily with zinc.

  • Kathleen Stallings

    Two brazil nuts a day may be too much. Two a week may be better. It is best to leave the shells on when storing and keep them in a cool, dry place. They can become rancid which can cause harm.

  • daz

    here’s another study (from 2015) that may be worthy for the ‘Drawbacks of Selenium’ section…if you have ‘nonmetastatic prostate cancer’…

    “Selenium Supplementation and Prostate Cancer Mortality”
    from the abstract;
    “Selenium supplementation of 140 or more μg/day after diagnosis of nonmetastatic prostate cancer *may* increase risk of prostate cancer mortality.
    Caution is warranted regarding usage of such supplements among men with prostate cancer.”

    1. Joseph M. Cohen

      Thanks 🙂

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