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Vitamin D is being discussed more and more in the health community for its importance to the human body. But today I want to talk about another nutrient that is often forgotten — selenium. Selenium is a critical nutrient for metabolism and overall health, but many people don’t know much about it (or why it’s so important).
What Is Selenium?
Selenium is a mineral that is critical for overall health. Selenium deficiency is fairly rare in the U.S but is an increasing problem in some areas of Europe and other selenium-deficient parts of the world. Also, selenium inadequacy (not getting enough selenium, but not deficient) may be a problem too.
An article published in Microbial Ecology in Health and Disease reports that 500 million to 1 billion people worldwide are deficient in selenium. Even more are not getting enough selenium for optimal health (though they aren’t technically deficient).
How Selenium Benefits the Body
Selenium is a powerful antioxidant that affects many functions in the body:
Reduces Risk of Cancer
Some research suggests that adequate selenium levels can have a protective effect against cancer. A 1996 double-blind (neither the researchers nor the participants knew who was getting selenium and who was getting a placebo) study found that selenium intake was linked to a significant overall lowered risk of dying from cancer and total cancer incidences. Because of this significant difference, the blinded part of the trial was ended early. That means that the researchers no longer thought it was ethical to assign some people to placebo.
According to Physicians Committee for Responsible Medicine, selenium helps defend against cancer in the following ways:
- Helps antioxidants fight free radicals that harm cells
- Slows tumor growth
- Speeds cancer cell removal
While this important study is fairly old, newer research supports its finding. A 2016 meta-analysis found that high intake of selenium in the diet was associated with decreased risk of cancer.
Improves Thyroid and Metabolism
Thyroid function is vital for a healthy metabolism. Selenium plays an important role in thyroid health.
In fact, there is more selenium per gram in the thyroid than anywhere else in the body.
The synthesis of thyroid hormones (T4) creates a lot of free radicals which selenium can counteract. Without selenium to do this job, oxidative stress (and related issues) can occur.
Selenium is also needed for hormone regulation. T4 is not bioactive until it is acted on by certain enzymes and converted to T3. These enzymes need selenium to function properly.
T3 is what sets the body’s metabolic rate. If anything gets “messed up” during this complicated process, thyroid and metabolic function can suffer.
Additionally, many with Hashimoto’s disease (an autoimmune thyroid condition) cannot tolerate iodine. But iodine is one nutrient necessary for thyroid hormone synthesis! The thought is that iodine supplementation reduces an important enzyme needed for T4/T3 conversion. Obviously, this creates a problem. But a systematic review shows that selenium intake may help with Hashimoto’s disease by reducing thyroid antibodies. Perhaps this is because selenium helps fight the free radicals created during T4 synthesis.
Bottom Line: Selenium intake may help reduce Hashimoto’s symptoms and the issues surrounding iodine intake. But always check with your doctor. There is a delicate balance between too much and not enough of both selenium and iodine for Hashimoto’s patients.
There has been a lot of research surrounding male fertility and selenium levels. Most of it suggests that selenium deficiency is one reason for male infertility. One study published in the Lancet shows that selenium improves male fertility by helping sperm motility.
Less focus has been on selenium intake and female fertility though. One study found that selenium deficiency may cause male and female infertility, miscarriage, preeclampsia, fetal growth restriction, preterm labor, gestational diabetes, and obstetric cholestasis (a liver and bile issue). This is an especially interesting finding considering many of these issues are not easily attributed to a cause.
Selenium is an important building block in glutathione production. Glutathione is the “master antioxidant” that helps the body produce and recycle antioxidants. This is vital for cellular health. It also binds with heavy metals and other toxins and helps them move to the stool to be excreted. There’s a lot of research showing that selenium intake can help with heavy metal detoxification.
May Reduce Cardiovascular Disease
It’s thought that selenium’s importance in reducing oxidative stress is one reason that selenium can help reduce heart disease. Selenium has also been shown to reduce inflammation, prevent the oxidation of cholesterol particles, and prevent blood platelets from clumping, according to a 2001 study.
However, research focusing on selenium’s direct relationship to heart disease is conflicting. One 2006 study found that there was no association between selenium levels and heart disease. A meta-analysis concluded that low selenium concentrations were associated with coronary heart disease. However, more research is needed.
A study published in the International Journal of Cardiology found that supplementing with selenium and CoQ10 at the same time had a significant effect on reducing heart disease mortality. So perhaps the combination of these two supplements is the key.
Improves Immune System Function
Selenium is incredibly important for immune function but it’s not completely understood how it works. What we do know is that selenium-deficient lymphocytes (white blood cells of the immune system) are less able to proliferate in response to cell division. Also, selenium helps remove toxins from the body and fight free radicals. This eases the burden on the immune system.
Viral and bacterial infections can be more serious in the presence of a selenium deficiency. For example, benign strains of Coxsackie and Influenza viruses can mutate to highly pathogenic strains. Additionally, people with HIV saw therapeutic outcomes improve with selenium supplementation.
Signs of Selenium Deficiency
Selenium is usually easy to get from a healthy diet, but in some cases, selenium may be low in food grown in selenium-poor soil. In the U.S., the soil is usually high enough in selenium (except for a few places including the Northwest and New England).
Signs of deficiency include:
- abnormalities of the skin, fingernails, hair, and blood cells
- male infertility
- heart disease (Keshan disease)
- arthritis (Kashin-Beck disease)
People at highest risk for selenium deficiency are those living in areas that are deficient, undergoing kidney dialysis, HIV positive, or those whose diet is primarily processed foods (processing destroys selenium).
Selenium deficiency or inadequacy is often more harmful in individuals with other health issues. Selenium deficiency produces biochemical changes that can predispose people to certain diseases. Additionally, selenium deficiency can make iodine deficiency worse.
Signs of Selenium Toxicity
Selenium is a critical nutrient for optimal health, but too much can be harmful. The balancing act of selenium is very delicate. I wouldn’t recommend supplementing without advice from your doctor first. Selenium from food sources should be fine if you’re eating a balanced diet.
Selenium toxicity can cause:
- Garlic breath
- Skin rashes
- Metallic taste in the mouth
- Brittle hair or nails
- Loss of hair or nails
- Discolored teeth
- Nervous system problems
Severe symptoms include difficulty breathing, tremors, kidney failure, heart attack, and heart failure.
Food Sources of Selenium
Selenium, unlike most other vitamins, can become toxic at relatively low levels. That’s why it’s especially important to get selenium from the diet instead of supplementation. Luckily it’s pretty easy to get enough selenium on a whole-foods diet as long as you live in an area not suffering from low selenium in the soil. Here are some of the best sources:
- Brazil nuts – The best source of selenium, brazil nuts average almost 2 days worth of selenium in one nut (the RDA for selenium is about 55 mcg).
- Brussels sprouts
- Sunflower seeds
- Chia seeds
- Pasture raised poultry
- Grass fed beef
- Pastured eggs
- Wild caught salmon
- Lamb or beef liver
The best way to add selenium to the diet is to seek out natural food sources and eat a variety of them each week. Eating in season or a produce delivery subscription can be a great solution.
As always, balance and individualizing diet to your needs (maybe under the care of a nutritionist or doctor if you have a thyroid or other condition) is best!
This article was medically reviewed by Dr. Lauren Jefferis, board certified in Internal Medicine and Pediatrics. As always, this is not personal medical advice and we recommend that you talk with your doctor or work with a doctor at SteadyMD.
Have you increased your selenium intake? What have you noticed about your health?
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