Selenium & Health
What is Selenium & What Does it Do?
Selenium is a mineral, which is a non-organic element found within the rocks and soil of the Earth. It is necessary for life and plays major roles in our body including our “reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection.” (1)
Selenium is a major component of gypsum, the mineral that makes up many crystals and is a key ingredient in chalk.
Selenium Deficiency:
Selenium deficiency is relatively uncommon in the U.S., as our soil is not deficient in selenium and most multivitamins contain our daily requirement of selenium. In areas of China however, selenium deficiency has been more common due to low selenium levels in the soil. Thankfully, the Chinese government instituted selenium supplementation policies in the 1970s, so this is much less common now. (1)
Selenium deficiency on its own does not cause disease or significant symptoms; however, it does reduce one’s ability to adapt to physical stress – like infection. (2) This lowered stress tolerance causes an increased risk of illness. The most well documented diseases that can result from prolonged selenium deficiency include:
Keshan disease: a fatal form of heart disease that results in a dilated and weak heart that cannot pump blood effectively. (2)
Kashin-Beck disease: a form of osteoarthritis that can affect children as young as two years of age and results in dwarfism and joint deformity. (2)
Those at Increased Risk of Selenium Deficiency:
Living in an area with selenium-deficient soil and not receiving selenium supplementation. Tibet, northern and central China, North Korea, and southeastern Siberia are the areas where selenium is significantly lacking in the soil. (2)
Following bariatric surgery. (2)
People living with severe inflammatory bowel disease such as Crohn’s disease. (2)
People undergoing kidney dialysis. (1)
People living with HIV. (1)
Where to Find Selenium:
Selenium can be found in a wide range of foods. The content of selenium in plant foods is highly influenced by the selenium content of the soil and can vary widely. In animal products, the selenium content tends to remain more consistent. (1)
Foods particularly rich in selenium: (1,2)
Brazil nuts - by far the highest
Tuna
Oysters
Clams
Halibut
Shrimp
Salmon
Cottage cheese
Brown rice
Sunflower seeds
Eggs
Whole wheat bread (5x more selenium than white bread!) (3)
Baked beans
Oatmeal
Selenium is also a regular component of multivitamin supplements.
Daily Intake:
The RDA (recommended daily allowance) of selenium is 55 mcg for adults and adolescents. This increases to 60 mcg during pregnancy, and 70 mcg with lactation. (2)
Toxicity:
Selenium toxicity should be avoided just as much as selenium deficiency. The upper intake level to avoid toxicity is 400 mcg daily. Acute and fatal toxicities have been reported due to accidental overdose of mislabeled supplements! Chronic selenium toxicity (selenosis) can develop with repeated supplementation of more than 400 mcg of selenium daily. (2)
Symptoms of selenosis include: (1,2)
Brittle hair and nails
Hair and nail loss
Gastrointestinal disturbances
Skin rashes
Garlic breath (when not eating garlic)
Metallic taste in the mouth
Fatigue
Irritability
Neurological disorders
Mottled teeth
Prevention and Treatment of Disease:
Due to the antioxidant activity of selenium and the many roles it plays, there has been quite a bit of research into using selenium to prevent or treat disease.
Disease Prevention:
Cancer:
Early research showed promise in the use of selenium in cancer prevention. Those with a higher intake of selenium from food, showed a reduced risk for colorectal, lung, esophageal, prostate, skin and gastric cancers. (1) Unfortunately, trials of using selenium supplements to reduce cancer risk have not shown the same results. In fact, in some studies of selenium supplementation, the risk of squamous cell carcinoma (a skin cancer from sun exposure) was increased by 25%! (2)
Here we see an example of the difference between getting your nutrients from a healthy diet and getting them from supplements. Remember, you cannot supplement yourself out of the consequences of a poor diet! This is one major reason why everyone needs access to healthy food!
Cardiovascular Disease:
Due to its high antioxidant activity, selenium should play a key role in reducing cholesterol oxidation and cardiovascular disease. Unfortunately, when this theory is put to the test, it doesn't prove to be true, and in fact, some studies show high levels of selenium in the blood associated with an increased risk of cardiovascular disease! (2)
This is an important example of how theories must be put to the test. Some theories are proven true, and others are proven false. Many of the self-help health books you may come across are filled with theories that sound good and may be supported by a few studies; however, they may not reflect the whole truth. Remember to ask yourself what the person providing you information stands to gain. What are they selling? Many of us are increasingly skeptical of the pharmaceutical industry and the information they present, but some of us forget that supplement companies, specialty testing companies, book sellers, and yes, even doctors, often use theories to sell expensive products - just like the drug manufacturers.
This is an ethical dilemma that can result in cherry picking research and confirmation bias leading to exploitation.
Disease Treatment:
Immune Dysfunction and Infection:
Animal studies show a strong link between selenium and healthy immune function and inflammation. We see selenium playing roles in many different immune responses: innate immunity, antibody production, and T-cell response. We also see selenium involvement in eicosanoid production. Eicosanoids are key molecules made from fatty acids that are involved in the regulation of inflammation. (2) Due to this information, researchers propose that selenium supplementation may be useful in diseases of immune dysfunction and chronic inflammation. Let’s see what the research has found so far:
HIV/AIDS:
Research in populations that are at risk of malnutrition have shown a slowed progression of HIV infection to AIDS diagnosis and fewer hospitalizations for those receiving selenium supplementation (200 mcg daily). The best results were in those receiving a multivitamin and additional selenium. (2)
Sepsis:
Preliminary clinical trials and meta analyses have shown a significant (17-27%) reduction in death due to sepsis in those given IV selenium treatment. (2)
Autoimmune Thyroid Diseases:
Initial randomized placebo controlled trials show promise in the use of selenium supplementation in the treatment of both Hashimotos thyroiditis and Graves disease with a measurable reduction in antibody levels in Hashimotos and an improved quality of life for those with Graves disease. (2) More studies are needed, but the current research looks promising.
Cognitive Decline:
Because selenium levels naturally decline with age and inflammation in the brain has been associated with cognitive decline, selenium supplementation could be a possible treatment for maintaining cognitive health.
Unfortunately, research thus far has not shown a significant improvement in cognitive function with selenium supplementation alone. However, a large study in France with 4,447 participants did show improvements with a mixed antioxidant supplement containing moderate doses of vitamin C, vitamin E, vitamin A, selenium, and zinc. (1) The doses of these nutrients were similar to those found in a multivitamin supplement.
This is another example of how combined nutrition tends to have more benefit than focusing on single nutrients. This is also how we find our nutrients in our food!
Medication and Nutrient Interactions:
When it comes to nutrients, selenium doesn’t act alone. Vitamin C, vitamin E, copper, zinc, iron, and iodine all work in partnership with selenium to perform many of the functions of our body. Deficiency in one or more of these nutrients will result in a reduced function of the others. (2)
Medications that interfere with selenium metabolism include:
Valproic acid (2)
Cisplatin (2)
Medications that selenium supplementation can interact with with include:
Nitrofurantoin - reduced toxicity to animals (2)
Paraquat - reduced toxicity to animals (2)
Statin drugs - possible inhibition of function (2)
Cisplatin - possible reduction of side effects (1)
Applications:
This week, I hope you gleaned the following tidbits from my writing:
Selenium plays many important roles in the body and has antioxidant function.
Selenium deficiency is rare but has significant side effects. It is mostly related to low selenium levels in the soil.
Brazil nuts have the highest selenium content of any food.
Selenium toxicity can be deadly or lower one’s quality of life.
Brilliant theories about using nutrients for treatment must be put to the test to discover the truth behind them.
Nutrients do not work in isolation, so single nutrient supplements aren’t usually better than food or multivitamins - but they do make some people a lot of money!
Bonus tidbit:
In my practice, I tend to meet people who are supplementing with a handful of single nutrients much more often than those taking a simple multivitamin. This increases the risk of developing nutrient toxicity and deficiencies – or digestive irritation and difficulty metabolizing the excess nutrients. Often, this results in a confusing combination of symptoms that lead to some people taking even more supplements. When a two-week pill holiday is tried, they usually feel much better. Sometimes supplements are helpful, and sometimes they are harmful. Please be careful; oftentimes, the answer is less rather than more.
Next week:
Next week, we will explore the mineral sodium. Many of us can link high sodium intake with an increased risk of high blood pressure, but did you know that sodium is necessary for life and has some treatment applications too? Join me next week to learn more in our penultimate nutrient article.
To our health!
References:
National Institutes of Health, “Selenium - Fact Sheet for Professionals, updated March, 26, 2021; accessed February 9, 2022, https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/
Higdon, J, “Selenium” Linus Pauling Institute, 2001; last update: 2015; accessed February 9, 2022; https://lpi.oregonstate.edu/mic/minerals/selenium
Gaby, A; Nutritional Medicine, Fritz Perlburg Publishing, Concord, NH, 2011 pgs 166-169
