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Selenium (Se), one of the trace elements, is a nutritionally essential mineral that exert many important biological functions. Se is essential in the synthesis of selenoproteins such as glutathione peroxidase (GSH-Px) (participates in process of detoxification) and thioredoxin reductase, optimal function of the immune system, and optimal neuropsychological function. Se also acts as an antioxidant and as a regulator of metabolism. Selenium plays an important role in the control of thyroid hormone metabolism and proper reproductive performance as well. One of the most researched and studied functions of Se is cancer protection.
Selenium deficiency may cause reduced growth rates owing to a feedback response which lowers triiodothyronine mediated synthesis of growth hormone in the pituitary gland, whereas a combined deficiency of selenium and iodine exacerbates hypothyroidism. Two diseases which are associated with severe endemic Se deficiency in humans including Keshan disease (a disease of the heart muscle that afflicts children and women of child bearing age), and Kaschin-Beck disease (a deforming arthritis) occurs in rural areas of China and Russia (eastern Siberia) are linked to food systems with exceedingly low Se content. For example, Keshan disease has been found in many mountainous provinces of China where Se levels in soil are very low. The incidence of the disease has been dramatically reduced by the prophylactic administration of oral tablets containing Na2SeO3 or selenite-fortified table salt.
Most of the reported cases of human exposure to hazardous levels of Se have involved occupational exposure and accidental oral consumption of various inorganic Se compounds. Signs of toxicity, referred to as ‘selenosis’, include skin and nail changes, tooth decay, and nonspecific gastrointestinal and neurologic abnormalities.
The Recommended Dietary Allowances (RDAs) for selenium are 55 mcg/day for women, men, and adolescents (aged 14 to 18) and 20 to 30 mcg/day for children. For infants, the Adequate Intake (AI) is 15 to 20 mcg/day. The RDA during lactation is 70 mcg/day. Combs Jr GF stated that in order to provide regular adult intakes, at least 40 mcg/day is needed to support the maximal expression of the Se enzymes, and perhaps as much as 300 mcg/day to reduce risks of cancer.
Human obtains Se from foods, as selenoamino acids (selenomethionine, selenocysteine, and selenocystine). Thus, individuals with low intakes of protein will also have low intakes of Se. Se enters the food chain through plants. The selenium content of plant foods depends on the bioavailable selenium content of the soils in which they are grown. Selenium which is present in cereals and most vegetables (mainly in the form of selenomethionine) has a higher bioavailability than that observed in dairy products or meats. The Se content of fish is high, presenting a relatively high bioavailability and the same is true of seafoods. The top 10 selenium-rich foods are as follows:
| Rank | Food item | Serving size | Selenium content |
| 1 | Brazil nuts | 1 oz* | 543 mcg |
| 2 | Rice, white, long grain | 1 cup | 44 mcg |
| 3 | Egg noodles, cooked | 1 cup | 38 mcg |
| 4 | Wheat germ, toasted | 1/4 cup | 28 mcg |
| 5 | Sunflower seeds | 1/4 cup | 25 mcg |
| 6 | Tuna, canned | 1 oz | 22.79 mcg |
| 7 | Oysters, raw | 1 oz | 18.67 mcg |
| 8 | Chicken, breast, baked | 1 oz | 13 mcg |
| 9 | Shrimp, cooked | 1 oz | 11.23 mcg |
| 10 | Bread, whole-wheat, soft | 1 slice | 10.38 mcg |
| *1 oz = 28.35 g | |||
As one can see from the table, there are many kinds of foods that are good sources of dietary selenium. In order to maintain a healthy body, a balanced diet is essential.
Note: An educational article about foods and nutrition by Pattamapan Lomarat (B.Sc. in Pharmaceutical Sciences), Department of Food Chemistry. Edited by N. & V. P. of U.K.
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Antioxidants are compounds in foods that prevent cell damage caused by free radicals.
Free radicals are normal byproducts of processes like metabolism that occur in your body on a daily basis.
They often get a bad rap, but free radicals are actually essential for health. They perform important functions, including protecting the body from disease.
However, things like smoking, alcohol use and stress can cause an excess of free radicals. This leads to oxidative stress, which damages healthy cells (1).
Oxidative stress has been linked to chronic diseases like heart disease, Alzheimer’s disease and cancer, as well as premature aging and the risk of stroke (2, 3, 4, 5, 6).
Antioxidants like selenium help reduce oxidative stress by keeping free radical numbers in check.
They work by neutralizing excess free radicals and protecting cells from damage caused by oxidative stress.
In addition to decreasing oxidative stress in the body, selenium may help lower the risk of certain cancers.
This has been attributed to selenium's ability to reduce DNA damage and oxidative stress, boost the immune system and destroy cancer cells (7).
A review of 69 studies that included over 350,000 people found that having a high blood level of selenium defended against certain types of cancer, including breast, lung, colon and prostate cancers (8).
It’s important to note that this effect was only associated with selenium obtained through foods, not supplements.
However, some research suggests that supplementing with selenium may reduce side effects in people undergoing radiation therapy.
For example, one study found that oral selenium supplements improved overall quality of life and reduced radiation-induced diarrhea in women with cervical and uterine cancer (9).
A diet rich in selenium may help keep your heart healthy, as low selenium levels have been linked to an increased risk of coronary artery disease.
In an analysis of 25 observational studies, a 50% increase in blood selenium levels was associated with a 24% reduction in coronary artery disease (10).
Selenium may also lower markers of inflammation in the body, one of the main risk factors for heart disease.
For example, a review of 16 controlled studies including over 433,000 people with coronary heart disease showed that taking selenium supplements decreased levels of the inflammatory marker CRP.
Additionally, it increased levels of glutathione peroxidase, a powerful antioxidant (11).
This indicates that selenium may help lower heart disease risk by reducing inflammation and oxidative stress in the body. Oxidative stress and inflammation have been linked to atherosclerosis, or the buildup of plaque in the arteries.
Atherosclerosis can lead to dangerous health problems like strokes, heart attacks and coronary artery disease (12).
Incorporating selenium-rich foods into your diet is a great way to keep levels of oxidative stress and inflammation to a minimum.
SUMMARYSelenium may help keep your heart healthy by keeping oxidative stress in check and reducing the risk of coronary artery disease.
Alzheimer’s disease is a devastating condition that causes memory loss and negatively affects thinking and behavior. It is the sixth leading cause of death in the United States.
The number of people with Alzheimer’s disease is growing. Thus, finding ways to prevent this degenerative disease is imperative.
Oxidative stress is believed to be involved in both the onset and the progression of neurological diseases like Parkinson’s, multiple sclerosis and Alzheimer’s disease (13).
Several studies have shown that patients with Alzheimer’s disease have lower blood levels of selenium (14, 15).
Additionally, some studies have shown that selenium in both food and supplements may improve memory in patients with Alzheimer’s disease (16).
One small study found that supplementing with one selenium-rich Brazil nut per day improved verbal fluency and other mental functions in patients with mild cognitive impairment (17).
What’s more, the Mediterranean diet, which is rich in high-selenium foods like seafood and nuts, has been associated with a lower risk of developing Alzheimer’s disease (18, 19).
SUMMARYA diet rich in selenium may help prevent mental decline and improve memory loss in people with Alzheimer’s disease.
Selenium is important for the proper functioning of the thyroid gland. In fact, thyroid tissue contains a higher amount of selenium than any other organ in the human body (20).
This powerful mineral helps protect the thyroid against oxidative damage and also plays an essential role in the production of thyroid hormones.
A healthy thyroid gland is important because it regulates metabolism and controls growth and development in the body (21).
Selenium deficiency has been associated with thyroid conditions like Hashimoto’s thyroiditis, a type of hypothyroidism in which the immune system attacks the thyroid gland.
An observational study of over 6,000 people found that low serum levels of selenium were associated with an increased risk of autoimmune thyroiditis and hypothyroidism (22).
Additionally, some studies have shown that selenium supplements may benefit people diagnosed with Hashimoto’s disease.
One review found that taking selenium supplements daily for three months resulted in lower thyroid antibodies. It also led to improvements in mood and general well-being in patients with Hashimoto’s disease (23).
However, more research is needed before selenium supplements can be recommended for those with Hashimoto’s disease.
SUMMARYSelenium protects the thyroid gland from oxidative stress and is necessary for thyroid hormone production. Selenium may be helpful for people with Hashimoto’s disease and other types of thyroid disease, but more research is needed.
The immune system keeps the body healthy by identifying and fighting off potential threats. These include bacteria, viruses and parasites.
Selenium plays an important role in the health of the immune system. This antioxidant helps lower oxidative stress in the body, which reduces inflammation and enhances immunity.
Studies have demonstrated that increased blood levels of selenium are associated with enhanced immune response.
On the other hand, deficiency has been shown to negatively impact immune cells and may lead to a slower immune response (24).
Studies have also associated deficiency with an increased risk of death and disease progression in people with HIV, while supplements have been shown to lead to fewer hospitalizations and an improvement in symptoms for these patients (25).
Additionally, selenium supplements may help strengthen the immune system in patients with influenza, tuberculosis and hepatitis C (26).
SUMMARYSelenium is crucial for the health and proper functioning of the immune system. Higher levels of selenium may be beneficial for boosting the immune system in patients with HIV, influenza, tuberculosis and hepatitis C.
Asthma is a chronic disease that affects the airways that carry air in and out of the lungs.
These airways become inflamed and begin to narrow, causing symptoms like wheezing, shortness of breath, chest tightness and coughing (27).
Asthma has been associated with increased levels of oxidative stress and inflammation in the body (28).
Due to selenium's ability to lower inflammation in the body, some studies suggest that this mineral may be effective in reducing asthma-related symptoms.
Research suggests that people who have asthma have lower blood levels of selenium.
In fact, one study showed that asthmatic patients with higher levels of blood selenium had better lung function than those with lower levels (29).
Selenium supplements may also be beneficial for reducing asthma-related symptoms.
For example, one study found that asthma patients given 200 mcg of selenium per day reduced their use of the corticosteroid medications used to control their symptoms (30).
However, research in this area is conflicting, and larger studies are needed to fully understand selenium’s role in the development and treatment of asthma (31).
SUMMARYSelenium may be beneficial for people with asthma due to its ability to lower inflammation in the body. However, more research is needed.
Asthma is a chronic disease that affects the airways that carry air in and out of the lungs.
These airways become inflamed and begin to narrow, causing symptoms like wheezing, shortness of breath, chest tightness and coughing (27).
Asthma has been associated with increased levels of oxidative stress and inflammation in the body (28).
Due to selenium's ability to lower inflammation in the body, some studies suggest that this mineral may be effective in reducing asthma-related symptoms.
Research suggests that people who have asthma have lower blood levels of selenium.
In fact, one study showed that asthmatic patients with higher levels of blood selenium had better lung function than those with lower levels (29).
Selenium supplements may also be beneficial for reducing asthma-related symptoms.
For example, one study found that asthma patients given 200 mcg of selenium per day reduced their use of the corticosteroid medications used to control their symptoms (30).
However, research in this area is conflicting, and larger studies are needed to fully understand selenium’s role in the development and treatment of asthma (31).
SUMMARYSelenium may be beneficial for people with asthma due to its ability to lower inflammation in the body. However, more research is needed.
Fortunately, there are many healthy foods that are high in selenium.
The following foods are great sources:
- Brazil nuts: 137% of the RDI in one nut (5 grams)
- Halibut: 106% of the RDI in 6 oz (159 grams)
- Yellowfin tuna: 77% of the RDI in 3 oz (85 grams)
- Oysters: 77% of the RDI in 3 oz (85 grams)
- Sunflower seeds: 62% of the RDI in 2 oz (56 grams)
- Shiitake mushrooms: 51% of the RDI in 1 cup (145 grams)
- Chicken: 50% of the RDI in 5 oz (140 grams)
- Eggs: 44% of the RDI in 2 large eggs (100 grams)
- Sardines: 36% in 4 sardines (48 grams)
The amount of selenium in plant-based foods can vary depending on the selenium content of the soil in which they were grown.
Thus, selenium concentrations in crops depend largely on where they are farmed.
For example, one study showed that the selenium concentration in Brazil nuts varied widely by region. While a single Brazil nut from one region provided up to 288% of the recommended intake, others provided only 11% (32).
This is why it is important to consume a varied diet that includes more than one good source of this important mineral.
SUMMARYFoods rich in selenium include seafood, nuts and mushrooms. It is important to consume a variety of foods that contain this mineral since selenium content can vary depending on growing conditions.
Although selenium is necessary for health, getting too much can be dangerous. In fact, consuming high doses of selenium can be toxic and even fatal.
While selenium toxicity is rare, it is important to stay close to the recommended amount of 55 mcg per day and never exceed the tolerable upper limit of 400 mcg per day (33).
Brazil nuts contain a very high amount of selenium. Consuming too many could lead to selenium toxicity.
However, toxicity is more likely to happen from taking supplements rather than from eating selenium-containing foods.
Signs of selenium toxicity include:
- Hair loss
- Dizziness
- Nausea
- Vomiting
- Facial flushing
- Tremors
- Muscle soreness
In severe cases, acute selenium toxicity can lead to serious intestinal and neurological symptoms, heart attack, kidney failure and death (34).
SUMMARYWhile selenium toxicity is rare, overconsumption of this mineral through diet or supplements can have dangerous side effects.
Selenium is a powerful mineral that is essential for the proper functioning of the body.
For starters, it plays a critical role in metabolism and thyroid function. It also helps protect the body from damage caused by oxidative stress.
Not only is selenium necessary for health, but it may also help boost the immune system, slow age-related mental decline and even reduce the risk of heart disease.
This micronutrient can be found in a wide variety of foods from oysters to mushrooms.
Adding more selenium-rich foods to your diet is an excellent way to maintain good health.
Selenium is a mineral found in the soil. Selenium naturally appears in water and some foods. While people only need a very small amount, selenium plays a key role in the metabolism.
Why do people take selenium?
Selenium has attracted attention because of its antioxidant properties. Antioxidants protect cells from damage. Evidence that selenium supplements may reduce the odds of prostate cancer has been mixed, but most studies suggest there is no real benefit. Selenium does not seem to affect the risk of colorectal or lung cancer. But beware: some studies suggest that selenium may increase the risk of non-melanoma skin cancer.
Among healthy people in the U.S., selenium deficiencies are uncommon. But some health conditions -- such as HIV, Crohn's disease, and others -- are associated with low selenium levels. People who are fed intravenously are also at risk for low selenium. Doctors sometimes suggest that people with these conditions use selenium supplements.
Selenium has also been studied for the treatment of dozens of conditions. They range from asthma to arthritis to dandruff to infertility. However, the results have been inconclusive.
How much selenium should you take?
The recommended dietary allowance (RDA) includes the total amount of selenium you should get from foods and from any supplements you take. Most people can get their RDA of selenium from food.
In studies to determine if selenium could aid in prostate cancer prevention, men took 200 micrograms daily.
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The safe upper limit for selenium is 400 micrograms a day in adults. Anything above that is considered an overdose.
Group |
Recommended Dietary Allowance |
| Children 1-3 | 20 micrograms/day |
| Children 4-8 | 30 micrograms/day |
| Children 9-13 | 40 micrograms/day |
| Adults and children 14 and up | 55 micrograms/day |
| Pregnant women | 60 micrograms/day |
| Breastfeeding women | 70 micrograms/day |
Can you get selenium naturally from foods?
Selenium content of food is largely dependent on location and soil conditions, which vary widely.
Good natural food sources of selenium include:
- Nuts, like Brazil nuts and walnuts
- Many fresh and saltwater fish, like tuna, cod, red snapper, and herring
- Beef and poultry
- Grains
Whole foods are the best sources of selenium. The mineral may be destroyed during processing.
What are the risks of taking selenium?
- Side effects. Taken at normal doses, selenium does not usually have side effects. An overdose of selenium may cause bad breath, fever, and nausea, as well as liver, kidneyand heart problems and other symptoms. At high enough levels, selenium could cause death.
- Interactions. Selenium may also interact with other medicines and supplements, such as some antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.
- Skin cancer. Selenium supplements may be associated with a risk of skin cancer (squamous cell carcinoma), so people at high risk of skin cancer should not take these supplements.
- Prostate Cancer. A study by the National Cancer Institute shows that men who already have high concentrations of selenium in their bodies nearly double their risk of aggressive prostate cancer if they take selenium supplements.
- Diabetes. One study found that people who took 200 micrograms a day of selenium were 50% more likely to develop type 2 diabetes. So far, it's unknown if the selenium actually caused the disease. Discuss the risk with your doctor.
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