Today we are covering selenium!

Selenium is all about resilience.

Resilience to stress, resilience to infection, and the ability to gracefully withstand the wear and tear imposed on our bodies slowly by aging and rapidly by disease.

The Strange Story Behind Selenium Studies

In fact, one of the strange puzzles about the history of selenium research is that it has gotten far, far harder to demonstrate harmful effects of selenium deficiency in lab rats than it was in the old days.

In the early twentieth century, selenium deficiency caused problems in lab rats that looked just like vitamin E deficiency. These included infertility and diseases involving oxidative damage to many different organs.

Nowadays, selenium deficiency doesn’t do much at all on its own. It makes lab animals more vulnerable to the effects of toxins, infections, and deficiencies of other nutrients, but without those additional stressors the deficiency itself stays silent.

What changed?

In the early 20th century, lab conditions were dirty. Researchers just kept the animals under a bench in the lab, or on top of one. Like the researchers themselves, the animals inhaled toxic vapors, and rolled around in dirt and chemical dust.

Nowadays, lab animals live much more luxurious lives. They are kept in specialized facilities that are sparkling clean. Researchers wear protective clothing to prevent pathogens from entering the facility. The air is filtered and ventilated, both to protect the animals from infections and to protect the researchers from becoming allergic to the animals. There’s a full-time veterinary staff, with someone on call 24/7, to check up on the animals, see if they’re getting sick, and help them if they are.

These days, lab animals are also far less likely to be accidentally deficient in other nutrients. Back in the day, they were fed “chow diets” that were just a bunch of cereal grains mixed together. Although domesticated mice and rats tend to do well on grain-heavy diets, grains can easily be deficient in various nutrients if grown in nutrient-poor soil, they’re quite low in protein and a handful of other nutrients that these animals need, and variations in their nutritional profiles make their exact vitamin and mineral content somewhat unpredictable.

After decades of research, and plenty of trial and error (some awfully big errors, in fact!), we now feed lab animals diets that are precisely controlled to deliver optimal amounts of each and every nutrient.

The Puzzle Continues in Humans

Just as in lab animals, selenium deficiency manifests in humans as vulnerability to other stressors.

The first well described selenium deficiency disease was Keshan disease. Keshan disease occurred in China. It caused liver damage, an enlarged heart, and the laying down of scar tissue in both organs, and caused people to lose their fingernails.

Although Keshan disease could be cured with selenium, it’s incidence appeared to go up and down seasonally. Further research showed that it went up and down as the presence of certain viruses waxed and waned. Researchers couldn’t produce Keshan disease in animals with selenium deficiency or viruses alone, but if they exposed selenium-deficient animals to the viruses associated with Keshan disease in humans, sure enough, the combination would cause Keshan disease in the animals.

In Tibet, North Korea, and parts of China and Siberia, selenium deficiency plays an important but less specific role in Kashin-Beck disease. This continues to affect about 2.5 million people beginning as early as age two, and causes arthritis, joint deformities, and dwarfism. In some areas, selenium supplementation prevents the disease, but in others it has no effect. It appears to be driven by an interaction between genetics, deficiencies of iodine and selenium, contamination of grains with mold toxins, and contamination of drinking water with fulvic acid, a compound from soil that can damage cartilage cells when present in excessive amounts.

In both humans and animals, then, selenium’s main role seems to be to provide resilience to other stressors.

Selenium Deficiency is a Laboratory of Virulence

One of the most shocking findings that came out of the research on selenium and viral infection is that selenium protects against not only infection, but also the transformation of viruses from relatively harmless forms to damaging forms.

The ability of a virus to harm its host is called virulence.

One of the viruses associated with Keshan disease is the coxsackie virus. Some strains of the coxsackie virus are relatively harmless, while some cause inflammation of the heart. These latter strains are said to be more virulent.

In mice with enough selenium, infection with a non-virulent strain of the coxsackie virus would remain relatively harmless. But in selenium-deficient mice, the non-virulent strain would morph into a virulent strain and cause heart inflammation.

There is some evidence that selenium deficiency also allows the flu virus to become more virulent, and it is possible this is true of viruses in general.

So, selenium deficiency doesn’t just make us more vulnerable to infection. It also turns us into walking laboratories of virulence, giving viruses a safe space to grow into the most harmful versions of themselves.

Selenium Protects Against Oxidative Stress

Selenium’s contribution to resilience is best explained by its role in our antioxidant system. This is the system that protects against oxidative stress, which is the natural wear and tear on our tissues that occurs in aging, and that increases with exposure to toxins, metabolic problems, and diseases. Selenium is required for nine different enzymes in this system.

In lab animals, selenium deficiency manifests when the animals are made deficient in vitamin E, given too much iron, or exposed to toxins and pathogens. Excess iron, toxins, and pathogens all worsen oxidative stress, and vitamin E is another key component of our antioxidant system. These interactions all make the centrality of selenium’s role in antioxidant protection clear.

Antioxidant protection is also central to the defense against infections. Our immune system makes hydrogen peroxide and even bleach (hypochlorous acid) to kill pathogens. Hydrogen peroxide and bleach, however, are also toxic to our immune cells. In order to be effective killing machines, our immune cells need plenty of selenium to protect themselves from their own weapons.

This explains why selenium-deficient populations become more vulnerable to certain viruses, and why the viruses become more virulent. Selenium-deficient people have more oxidative stress in their bodies. This is a messy and damaging environment that causes viral genes to mutate. However, the general, chronic oxidative stress in these people isn’t strong enough to actually kill the viruses. In fact, the poorer antioxidant protection of the immune cells renders them rather incompetent. If the mutations cause some of the viruses to become more dangerous, they will have an advantage over the less virulent ones and spread, and the immune system won’t have any souped-up killing machines to stop them.

Selenium Is Needed for Thyroid Health

It’s not just the immune system that makes hydrogen peroxide. So does the thyroid gland. Hydrogen peroxide is directly used in preparing iodine to make thyroid hormone, and the thyroid needs to protect itself from damage with selenium.

So, selenium is needed to allow adequate production of thyroid hormone and to protect the thyroid gland from oxidative damage.

In addition, selenium is required for three enzymes used outside of the thyroid gland to activate and deactivate thyroid hormone.

So, both in and outside of the thyroid gland, selenium is playing a role in allowing proper production and regulation of thyroid hormones.

This might explain selenium’s role in Kashin-Beck disease. As we discussed in the lesson on iodine, hypothyroidism in early development contributes to cretinism, which, among other problems, causes dwarfism. Hypothyroidism is also often associated with joint pain. Since Kashin-Beck disease generally involves deficiencies of both selenium and iodine, and causes dwarfism and arthritis, it is likely that selenium deficiency at least partly contributes to the disease by hurting the utilization of iodine and the production and regulation of thyroid hormone.

Selenium supplementation has also shown promise for two important autoimmune thyroid diseases: Hashimoto’s thyroiditis and Graves’ disease. Autoimmune diseases are those in which the body attacks itself with its own immune system. Each of these diseases involves the production of antibodies that attack the thyroid gland.

Hashimoto’s appears to start with inflammation and damage inside the thyroid gland driven by oxidative stress. It causes low or erratic levels of thyroid hormones. Graves’ disease generates antibodies that cause the thyroid gland to make too much thyroid hormone.

Several studies have shown that selenium supplements decrease antibody production in Hashimoto’s, and one study showed that they improve measures of well being in Graves’ disease. We still need more research to see whether selenium supplements can lower the need for medication or reverse the disease processes, but so far selenium has shown promise.

Other Roles of Selenium

Selenium plays a number of other important roles:

It protects sperm from oxidative damage and is therefore essential for male fertility.
It helps proteins fold into their correct shape, and helps degrade proteins that have misfolded. This alone allows thousands of different processes to run smoothly instead of getting jammed up.
It helps cells change their shape, move around, and respond to their environment when needed. While it’s antioxidant activity enables it to turn our immune cells into souped-up killing machines, this role in cell shape and movement helps those killing machines move swiftly against their targets and consume them.
When data scientists peer deep into the mysteries of the genome, they find evidence of 8 proteins that use selenium whose functions we don’t understand yet. So, selenium likely has even more roles than I’ve laid out here.
Selenium and the Soil

Although our food choices can help us get the right amount of selenium, the selenium story is more about the soil our food was grown in.

Selenium, more than any other mineral, varies dramatically in different soils.

Worse, there is very little logic to the variation.

With many minerals, their soil content has declined over time as we’ve depleted the soils more and more with intensive farming. With iodine, the evaporation and rainfall patterns dictate where it is found. With selenium, ancient, prehistoric geologic events have created enormous variation that persists to this day, largely resistant to farming practices and current climate and weather patterns.

Most people living in the United States are subject to a 20-fold variation in soil selenium. In other words, if you take a random sample of average folks, one person’s soil would have twenty times as much as another person’s soil, and most of those folks would lie somewhere in between.

In China, where selenium deficiency was first discovered has been described best, such a random sample of average folks is subject to a 450-fold variation instead of a 20-fold variation.

If we include some of the most extreme deviations found in the US, that number actually increases to an 800-fold variation.

Although we can make some general statements about where selenium is likely to be low or high, the picture is very complicated at the local level.

For example, in the United States, generally speaking, the Northwest, the Northeast, all of the states that border the Great Lakes including most of Illinois across the Atlantic Coast and Florida are low in selenium. By contrast, we tend to have adequate selenium throughout the Central and West Central United States and the South.

On the other hand, we have very high levels in South Dakota, Montana, Wyoming, Nebraska, Kansas, Utah, Colorado, and New Mexico.

But it gets very complicated in some states: for example, in Montana and New Mexico, we can have both very high and deficient levels of selenium in different local areas that lay side by side.

The picture becomes even more complicated when you consider where your food comes from.

Do you shop at the supermarket? If so, your food probably comes from all over the world, and you can just hope that if you eat a diverse diet it all averages out.

Do you shop exclusively at local farmers markets? If so, your food mostly comes from the same place and you may have too much, too little, or juuuuuuuuuust the right amount of selenium in your food, depending on where exactly it was grown.

This is concerning, because it means that we could all eat the same diet, but some of us would get just the right amount of selenium, some would get too much, and some would get too little.

This is all the more concerning because too much selenium can be toxic, and some of the signs of toxicity are similar to the signs of deficiency.

Signs of Selenium Deficiency and Toxicity

So what does deficiency and toxicity look like? Let’s take a look at what we should expect to find from each, and how to tell them apart.

Selenium Deficiency

As we already discussed, the classical deficiency disease is Keshan disease, and it involves liver damage, an enlarged heart, and the laying down of scar tissue in both organs. No one has clearly documented white streaks in the fingernails as a sign of deficiency, but in these very well documented extreme cases, the fingernails turn completely white and fall out. It is possible that, at more moderate levels of deficiency, white streaks appear.

Based on what we know selenium does in the body, and based on some studies of the effects of selenium supplements, we could also expect moderate deficiency to cause these problems:

Getting sick more often.
Infertility, especially in males.
Hashimoto’s, Graves’, and possibly many other types of thyroid problems.
Arthritis, especially the most common form, osteoarthritis.
Faster, less graceful aging.
An increased risk of most chronic diseases, especially cancer.
Selenium Toxicity

On the other hand, too much selenium is toxic. Selenium seems to act as an antioxidant when it partners up with proteins, but as an oxidant when it runs around by itself, free to cause mischief. Most of the problems of selenium toxicity are probably caused by increased oxidative stress, and this ability of selenium to contribute to the same problem it’s best at solving is probably why some of the signs of selenium deficiency and toxicity overlap.

As with deficiency, our best information about human selenium toxicity comes from China, where coal pollution has caused some soils to be more than 1000 times higher than the absolute highest amounts found in the United States.

In both deficiency and toxicity, we see damage and scar tissue deposits in the liver. In both cases, we see fingernails falling out.

In toxicity, however, we have much clearer documentation that the fingernail problems start with white spots and streaks and brittle nails before they outright fall out. And it’s not just the nails: the hair falls out too.

In the United States, the closest we have seen to this was decades ago when some people made math errors when making selenium supplements that caused them to be a thousand times higher than they were labeled. These supplements caused nausea, diarrhea, irritability, fatigue, loss of hair and nails, and tingling in the hands and feet.

While these extremes cases of toxicity are unlikely to occur with foods and supplements these days, we still have reasons to be concerned: in human trials, supplementation with 200 micrograms per day (mcg/d) reduced the risk of cancer in people who had low selenium levels, but it appeared to raise the risk of diabetes and maybe even cancer in people with high selenium levels.

The Importance of Measuring Blood Levels

In fact, the blood levels of selenium where diabetes and cancer risk start to increase are only 15-20 percent higher than the blood levels where cancer risk is lowest.

For most nutrients, the amounts that cause problems are far, far higher than the amounts that are needed to give us the biggest boost to our health. This makes it really easy to find a sweet spot without micromanaging anything.

For selenium, however, I recommend that everyone ask their doctor to have their blood levels checked. The correct test is plasma or serum selenium, the acceptable range is 90-140 micrograms per liter (mcg/L), and the sweet spot is 100-120 mcg/L.

That soil variation is so enormous, and that some of the signs of deficiency and toxicity overlap, makes it all the more important to check selenium levels at least once, and to measure them again if you make substantial changes to your diet or move to a different location.

How Much Selenium Do We Need?

The RDA for selenium is based on maximizing blood markers of antioxidant protection, and was set in the year 2000 at 55 mcg/d for adults and adolescents over the age 14.

The RDA, in mcg/d, increases to 60 during pregnancy and 70 during lactation. For children, they adjusted downward based on bodyweight, reducing it to 40 for ages 9-13, 30 for ages 4-8, and 20 for ages 1-3.

For infants, they set an AI based on what is found in breast milk, yielding 15 for the first six months of life and 20 for the next six months.

If the RDA were revised, it would most likely be based on more recent research on the amount needed to maximize a protein made by the liver that transports selenium to the brain and male reproductive tissues and prevents its loss in the urine. This would raise the adult RDA to 75 mcg/d.

The cancer studies suggest 120 mcg/d is the best amount to reduce the risk of cancer without increasing the risk of diabetes. Since this appears to be the best amount for reducing the risk of chronic disease without causing side effects, I recommend using this as our target. To adjust downward for children, I recommend aiming for 60 mcg for every 1000 Calories.

Selenium in Foods: General Principles

Now let’s talk about how to get enough selenium from foods. Here are a few general principles:

Plants don’t require selenium as an essential nutrient, and take it up randomly from the soil. As a result, their selenium content is entirely dictated by the soil content, and the variation can be as high as 100-fold.

Brazil nuts, often touted as the best source of selenium, can have as little as 8 mcg per nut and as much as 220 mcg per nut. You could eat 5 Brazil nuts a day, and in some cases you wouldn’t be getting enough and in others you’d be getting far too much. I recommend limiting Brazil nuts to no more than two a day, and not relying completely on them for selenium. The one exception is if you contact the manufacturer to see if they have conducted tests on the exact selenium contents of their nuts and the variation from batch to batch, and you can be sure exactly how much you are getting.

Animals require selenium, so they regulate how much they absorb from food and eliminate the excess through their detoxification systems. As a result, they are far less variable than plants: only 2-5-fold, instead of 100-fold. As a result, animal foods are a more consistent and reliable source of selenium than plant foods are.
Still, 2-5-fold variation is a lot. Even if you get your selenium from animal foods, you should still have your doctor check your selenium levels.

Organ meats, especially kidney, are the best animal source of selenium. They are followed by eggs, cheese (but not other dairy products), and seafoods.

While seafoods are a good source of selenium, about half of that selenium is bound up with mercury. This is good, because it protects us from the mercury. However, it also makes the selenium in seafoods only about half as absorbable as the selenium in other animal foods.

Among plant foods, legumes, grains, nuts, and seeds tend to be decent sources of selenium, while fruits, vegetables, spices, mushrooms, and sweeteners are poor sources.

Mushrooms are much poorer sources of selenium than they appear to be when looking at a nutritional database, because the selenium is bound up in ways that make it very hard to absorb and use. The bioavailability of selenium from mushrooms is only about five percent.
Selenium in Foods: The Five Tiers

Now let’s get specific and break all the foods down into five tiers.

As we look at these tiers, we should regard these numbers as typical or average, and realize that the actual foods we are eating could deviate substantially. In general, the animal foods we consume will be much more consistently closer to these numbers than the plant foods.

To account for the lower bioavailability of selenium in seafoods and mushrooms, I cut the amount in seafoods in half and the amount in mushrooms by 95%. For spices, a serving is considered two grams rather than 100 grams. No mushrooms or spices wound up making the cut when considered this way.

For the tiering, our target is 120 mcg/d, the amount associated with maximal reduction in cancer risk.

Tier 1

Tier 1 foods contain at least 120 mcg per 100 grams (g), allowing us to meet the target in a single serving.

For animal foods, this includes kidneys from beef, pork, or lamb; the liver, heart, and kidney of Alaskan sea lion; and turkey giblets.

For plant foods, this includes Brazil nuts.

Tier 2

Tier 2 foods contain at least 40 mcg per 100 g, allowing us to meet the target in 2-3 servings.

Tier 2 contains a lot of organ meats, such as the livers of lamb, turkey, goose, duck, chicken, pork, and beef; liver-based products such as pork liverwurst and braunschweiger, and pate; beef and veal spleen; veal kidney; chicken giblets; beef lung; and pork pancreas.

Other animal foods in tier 2 include egg yolk, fat-free parmesan cheese, and some cuts of pork and ham, though most are in tier 3.

Tier 2 also contains two native Alaskan seafoods: sea lion meat with or without the fat, and whitefish eggs.

Many wheat products are in tier 2, including germ, bran, whole-grain flour, sprouted wheat, vital wheat gluten, bread flour, enriched semolina, durum, hard red winter and spring, and most pasta and noodles.

Other grain products in tier 2 include oat bran and soy flour.

Other plant products in tier 2 include dried sesame seed kernels, dried or toasted sunflower seed kernels, and smooth peanut butter.

Tier 3

Tier 3 provides at least 24 mcg per 100 g, allowing us to meet the target in 4-5 servings.

Tier 3 contains most cuts of pork and ham, though some are in tier 2. It also contains most cuts of beef, turkey, emu, and ostrich, though some are in tier 4. It contains several cuts of lamb (foreshank, leg, and loin, though most are in tier 4, and some are in tier 5), most cuts of certain game meats (bison, beaver, elk and rabbit, though some cuts from these animals are in tiers 4 and 5), and many deli meats.

Tier 3 also includes most whole eggs, such as those of chicken, goose, duck, turkey, and quail.

Some seafoods make it into tier 3 (oysters, black and red caviar, swordfish, and roughy orange).

Tier 3 contains a number of organ meats, such as the heart of turkey, veal, and lamb; the gizzard of turkey and chicken; the spleen and pancreas of lamb; pork stomach; and pork liver cheese.

Tier 3 also contains unsweetened gelatin powder.

For plant foods, tier 3 contains flax seeds and a number of grain products, (all-purpose white flour; white rice; rye flour, partially debranned oat flour, and most barley products).

Tier 4

Tier 4 foods provide at least 13.23 mcg per 100 g (except nutritional yeast, which is measured per two heaping tablespoons), allowing us to meet the target with 1-2 pounds of food per day.

Tier 4 contains two yummy treats: cocoa powder and molasses.

Egg whites also make it into tier 4.

Tier 4 contains most cuts of chicken, duck, goose, guinea hen, pheasant, and quail, although many cuts of chicken and some cuts of duck and turkey are in tier 5.

It contains some processed meats and some cuts of turkey, pork, ham, beef, and bison, though most are in higher tiers, and some are in tier 5.

The majority of cheeses are in tier 4 (mozzarella, most parmesan, Swiss, ricotta, American, cheddar, blue, brick, brie, camembert, caraway, cheshire, colby, edam, feta, fontina, gjetost, gouda , gruyere, limburger, colby, queso anejo, queso asadero, queso chihuahua, monterey, muenster, pimento, port de salut, provolone, romano, roquefort, and tilsit) though fat-free parmesan is in tier 2, and some cheeses are in tier 5 or don’t make the cut.

Tier 4 contains pork feet and a number of organ meats (calf liver; beef heart; the brains of beef and pork; the lungs of pork and veal; the thymus of beef and veal; and lamb tongue).

A number of crustaceans make it into tier 4: lobster, abalone, cuttlefish, mussels, octopus, squid, whelk, shrimp, crab, crayfish, and snail.

The vast majority of fish are in tier 4: wild salmon, mackerel, haddock, Atlantic ocean perch, tilapia, fish roe, snapper, European anchovy, striped and sea bass, bluefish, butterfish, cod, Atlantic croaker, cusk, dolphinfish, grouper, halibut, herring, monkfish, striped mullet, pollock, Florida pompano, pout, Pacific rockfish, sablefish, scup, seatrout, American shad, shark, sheepshead, smelt, spot, tilefish, fresh tuna, European turbot, Atlantic wolffish, yellowtail, flatfish, surimi, and sheefish. Beluga whale is also in tier 4.

2 heaping tablespoons of unfortified nutritional yeast makes it into tier 4.

For plant products, tier 4 contains three nuts (raw cashews, dried butternuts, and dried walnuts), several soy products (raw soybeans; soybean curd cheese; and hard nigari, raw firm, or fermented tofu), dried and unsweetened coconut meat, and garlic.

Tier 5

Tier 5 foods provide at least 5.29 mcg per 100 g, allowing us to meet the target with 3-5 pounds of food.

Tier 5 contains a yummy treat: Dutch processed cocoa powder.

Tier 5 contains some organ meats: beef tripe, veal or lamb brain, pork heart, and the tongue of pork, beef, or veal.

Although most fats and oils do not make the cut, pork fat makes it into tier 5.

Tier 5 contains many cuts of chicken, turkey skin, and some cuts of turkey and duck meat. It also contains 70% lean ground beef, goat, most cuts of lamb and veal, and some processed meats.

Tier 5 contains most cuts of most game meats (antelope, beefalo, wild boar, caribou, deer, elk, horse, moose, buffalo, muskrat, rabbit, squirrel, pigeon, and bear) though some elk cuts are in tier 3, some bison cuts are in tiers 3 and 4, and some other game meats are in tier 3.

Tier 5 contains frog legs, green turtle, clams, scallops, and a number of fish (farmed salmon, walleye pollock, freshwater bass, burbot, carp, catfish, cisco, drum, milkfish, northern pike, sturgeon, white sucker, pumpkin seed sunfish, rainbow trout, and eel.)

Tier 5 also contains low-fat or low-sodium Swiss cheese and most cottage cheese.

Among the plant products, tier 5 contains many beans: cranberry, French, great northern, pink, small white, white, yellow, navy, fava, hyacinth, moth, mung, mungo, winged, yardlong, and lima. It contains a number of other legumes: catjang and common cowpeas, chickpeas, lentils, lupins, and pigeon peas. It also contains many peanuts and peanut butters, and many soy products (soy flour, tofu yogurt, okara, natto, miso, and extra-firm, firm, raw regular, or soft tofu).

Tier 5 also contains dried hickorynuts, raw pistachios, dried pumpkin and squash seeds, dried sesame seeds, sesame and cashew butter, raw coconut meat, and raw coconut milk.

Foods That Don’t Make the Cut

Fruits, vegetables, mushrooms, and spices don’t make the cut. With the exception of molasses (tier 4), sweeteners don’t make the cut.

Cream cheese and goat cheese don’t make the cut. Non-cheese dairy products, such as butter, milk, buttermilk, yogurt, sour cream, and whey products don’t make the cut.

Chicken feet, chicken heart, and the ears, tails, and jowl of pigs don’t make the cut.

Lamb from New Zealand and Australia doesn’t make the cut.

Four beans (adzuki, black turtle soup, black, and kidney), two other legumes (split peas and immature cowpeas), and three legume products (soymilk, carob flour, and hummus) fail to make the cut.

Six nuts (almonds, walnuts, hazelnuts, macadamia nuts, pecans, and chestnuts), three seeds (dried breadnuttree, toasted sesame seed kernels, and dried pine nuts), and coconut water don’t make the cut.

Getting Enough Selenium Through Diet

Meeting the Requirement With Animal Foods

The best animal-based selenium superfood is kidneys. In fact, kidneys have so much selenium that it would be wise to limit them to no more than two servings per day (though you deserve some kind of reward if you’d eat two servings of kidneys per day!).

Seafoods are consistently good sources of selenium. If you love seafood, mixing and matching 1-2 pounds of the seafoods in tiers 3 and 4 will meet the selenium requirement.

Although liver is very high in selenium, getting enough from liver alone would require two to three servings per day, and liver should generally be limited to two servings per week to avoid overdosing on vitamin A and copper.

While many meats are great sources of selenium, the data is really all over the place, with many species having different cuts spread across tiers 3, 4, and 5.

Eggs and cheese (but not other dairy products) are much more consistent sources, but few of us are going to eat a pound of eggs or one to two pounds of cheese every day.

Although only kidneys stand out as a great way to meet the selenium requirement with a relatively small amount of animal foods, consuming 4-8 ounces of liver per week and mixing and matching one to two pounds per day of eggs, cheese, fish, shellfish, and meat will tend to meet the target collectively.

Meeting the Requirement With Plant Foods

For plant foods, Brazil nuts obviously dominate in tier 1, but remember the variation in plant foods is tremendous: five Brazil nuts from some soils won’t give you enough, and five from other soils will give you too much.

I would recommend limiting Brazil nuts to two a day, and not relying on them exclusively.

Wheat products are a distant but strong second place in tier 2, and most legumes, grains, nuts, and seeds fall somewhere in the five tiers and can be mixed and matched to meet the target.

Selenium Is Still About the Soil

While our analysis of these foods offers some general guidelines for getting enough, selenium is still more about the soil our food is grown in than our food selection. It’s important, therefore, to consider whether you have any signs and symptoms of deficiency and have your blood levels measured rather than relying on diet alone.

Should You Supplement With Selenium?

If you are unsure of your selenium status and want to be proactive about getting enough, taking 50 mcg/d would be the best choice. This is a good enough maintenance dose to keep you out of deficiency, and when combined with your diet, it will probably bring you close to the optimal target of 120 mcg/d.

Most supplements are 200 mcg. While these will benefit you if you have poor selenium status, they could raise the risk of diabetes and cancer if you already have good selenium status before you start supplementing. You can take two of these capsules per week to yield a little more than 50 mcg/d.

200 mcg/d may be warranted in the treatment of some diseases. This dose has been shown to lower antibodies in Hashimoto’s thyroiditis and improve well being in Graves’ disease. In HIV-infected patients, it decreases hospital admissions, stops the viral load from getting worse, and in infected pregnant women, it reduces the risk of death for the mother and child. Still, it is best to measure blood levels when using this dose.

In addition, medical use of intravenous selenium has been shown to reduce the risk of death in patients who are critically ill with severe inflammatory disorders, such as systemic inflammatory response syndrome (SIRS), sepsis, and septic shock.

What Form of Selenium is Best?

Selenium comes in a number of different forms:

Selenomethionine is most popular, is the form dominant in plants, and is a major form in yeast. It is perfectly effective at preventing and treating deficiency.

Selenium-enriched yeast has some selenomethionine, but it also contains a variety of other forms.

Selenite and selenate require more processing that selenomethionine to be used, and are less effective at treating deficiency.

Selenium methyl-L-selenocysteine is a detoxification product made by plants that are trying to get rid of selenium they have randomly taken up from the soil. This is almost certainly the least effective form and should be avoided.

The main form of selenium in animal foods is selenocysteine. This should not be confused with selenium methyl-L-selenocysteine. Selenocysteine is most likely the safest and most effective form because it’s the closest form to what we incorporate into our own proteins, and excesses of it are more easily eliminated from the body than selenomethionine. Unfortunately, selenocysteine is not available as a supplement.

Arguably the selenium from animal foods is best, but selenomethionine is the best out of the available supplements and research has shown it to be highly effective at preventing and treating deficiency. Therefore, I recommend using selenomethionine if you choose to supplement.

It’s Not Just About Selenium

The selenium story is first about soil and second about food choice, but these aren’t the only factors that impact selenium status:

Vitamin B6 is needed to incorporate selenium into our proteins.

Methylation, which depends mainly on folate, B12, and choline, is required in two ways to support selenium status. On the one hand, methylation is needed to make a protein that delivers selenium to the brain and male reproductive organs, and to prevent its loss in the urine. On the other hand, methylation is needed to get rid of excess selenium and prevent toxicity. So, we need methylation to make selenium both safe and effective.
To support antioxidant status, selenium cooperates with protein, vitamins E and C, zinc, copper, manganese, and iron.
To support thyroid hormone metabolism, selenium interacts with protein and iodine.

Wrapping Up

Okay, let’s wrap up!

Minerals Selenium creates resilience to stress. It is especially important for protecting us from viruses, and it’s deficiency makes us more vulnerable to infections, toxins, and other nutrient deficiencies.

Minerals Selenium is an important part of the antioxidant system, protects us from wear and tear as we age, is important to nearly every aspect of thyroid health, and protects against cancer.

Minerals Severe deficiency causes damage to the liver and heart and causes the fingernails to fall out. Streaks and white spots in the nails may be a sign of more moderate deficiency.

Minerals Toxicity causes brittle nails with streaks and white spots that may fall out, hair loss, liver damage, and tingling in the hands and feet.

Minerals Moderate excesses of selenium may raise the risk of diabetes and cancer.

Minerals The difference between the maximally beneficial amount of selenium and the amount where the risk of diabetes and cancer starts increasing is small. This emphasizes the need to measure blood levels. This is all the more important because selenium status is largely driven by soil variation, and it is hard to judge our selenium intake from our food choices alone.

Minerals The optimal target for selenium intake from food and supplements combined is 120 mcg/d for most adults. Those with Hashimoto’s, Grave’s, or HIV should consider supplementing, and doctors caring for critically ill patients with systemic inflammatory response syndrome (SIRS), sepsis, or septic shock should consider intravenous use.

Minerals Selenium is largely about the soil, but animal foods are more consistent than plant foods: animal foods vary 2-5-fold, while plant foods vary up to 100-fold.

Minerals For animal foods, kidneys are the best source, can meet the target in one serving per day, and are so high that they should be limited to two servings per day. 4-8 ounces of liver per week are a useful contribution. 1-2 pounds per day of eggs, cheese, seafood, and meat can, together, meet the target.

Minerals For plant foods, Brazil nuts are the best source, but Brazil nuts and all other plant foods are extremely variable. Unless you verify the exact selenium content of a given Brazil nut product, I recommend limiting them to two nuts per day. Diversifying several pounds of food across legumes, whole grains, nuts, and seeds offers the highest likelihood of hitting the selenium target with plants.

Minerals If you choose to supplement, use selenomethionine. If you aren’t treating a specific issue, use 200 mcg twice a week. For Hashimoto’s, Graves’, or HIV, use 200 mcg per day.

Minerals Vitamin B6, methylation nutrients (especially folate, B12, and choline), protein, iodine, vitamins E and C, zinc, copper, manganese, and iron are all important to utilizing selenium effectively.

Minerals Because the soil variation is so great, it is best to focus on keeping blood levels between 90 and 140 mcg/L, with the sweet spot being 100-120.