Seeking the Proper Level of Selenium

Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is incorporated into proteins to make selenoproteins that are important antioxidant enzymes. Other selenoproteins help regulate thyroid function and play a role in the immune system. Selenium is an important co-factor for the antioxidant enzyme glutathione-peroxidase, which helps boost the immune system, protect against cardiovascular disease, improve fertility, ward off the growth of cancerous cells, and increase thyroid metabolism. Selenium is also important for detoxification enzymes.

Selenium plays a vital role in metabolism, hormonal, antioxidant and immune functions. It initiates DNA repair in damaged cells, inhibits the proliferation of cancerous cells, and induces their death. Selenium works together with vitamin E, which is a powerful antioxidant. Together, they perform vital antioxidant functions throughout the body, which reduces the risk of heart disease and cancer, and reduces inflammation in cases of rheumatoid arthritis.

Plant foods are the major sources of selenium. Brazil nuts are the best natural source (100 grams of nuts provide about 1917 µg of selenium and 3485% of recommended daily intake). The content of selenium in food depends on the selenium content of the soil where plants are grown. For example, soils in the high plains of northern Nebraska and the Dakotas have very high levels of selenium, while soils in some parts of China and Russia have very low amounts of selenium. Likewise, the selenium content of foods can vary. For example, the U.S. Department of Agriculture Food Composition Database lists the selenium content of Brazil nuts as 544 mcg of selenium per ounce, but values from other analyses vary widely. You should eat no more than one Brazil nut per day because of their very high selenium content. Selected food sources of selenium are provided in the following table.

Sources of Selenium
Food Micrograms
Brazil nuts, dried, unblanched, 1 nut 96 137
Sunflower seed kernels, dry roasted, 1 ounce 23 33
Macaroni, enriched, boiled, ½ cup 19 27
Crimini mushrooms, sliced, 1 cup 19 27
Oatmeal, instant, fortified, cooked, 1 cup 12 17
Bread, whole-wheat, commercially prepared, 1 slice 11 16
Rice, brown, long-grain, cooked, ½ cup 10 14
Rice, white, enriched, long-grain, cooked, ½ cup 6 9
Bread, white, commercially prepared, 1 slice 6 9
Walnuts, black, dried, 1 ounce 5 7
Mustard seeds, ground 1 teaspoon 4.2 6

*DV = Daily Value. DVs are reference numbers developed by the Food and Drug Administration (FDA) to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for selenium is 70 micrograms (mcg). Most food labels do not list a food’s selenium content. The percent DV (%DV) listed on the table indicates the percentage of the DV provided in one serving. A food providing 5% of the DV or less is a low source while a food that provides 10–19% of the DV is a good source. A food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet. For foods not listed in this table, please refer to the U.S. Department of Agriculture’s Nutrient Database Web site.

Death from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher blood levels or intake of selenium. In addition, the incidence of nonmelanoma skin cancer is significantly higher in areas of the United States with low soil selenium content. Selenium might affect cancer risk in two ways. As an anti-oxidant, selenium can help protect the body from damaging effects of free radicals. Selenium may also prevent or slow tumor growth. Certain breakdown products of selenium are believed to prevent tumor growth by enhancing immune cell activity and suppressing development of blood vessels to the tumor.

Selenium is one of a group of antioxidants that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease.

Surveys indicate that individuals with rheumatoid arthritis, a chronic disease that causes pain, stiffness, swelling, and loss of function in joints, have reduced selenium levels in their blood. In addition, some individuals with arthritis have a low selenium intake. Your body’s immune system naturally makes free radicals that can help destroy invading organisms and damaged tissue, but that can also harm healthy tissue. Selenium, as an antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals.

High blood levels of selenium (>100 mcg/dL) can result in a condition called selenosis. Symptoms of selenosis include gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage. The Institute of Medicine of the National Academy of Sciences has set a tolerable upper intake level (UL) for selenium at 400 micrograms per day for adults to prevent the risk of developing selenosis.

Selenium toxicity is rare in the United States. The few reported cases have been associated with industrial accidents and a manufacturing error that led to an excessively high dose of selenium in a supplement. As noted earlier, Brazil nuts contain very high amounts of selenium (68 to 91 mcg per nut), so limit yourself to one nut per day.

This blog uses the latest nutritional data available from the USDA (United States Department of Agriculture), and the FDA (United States Food and Drug Administration), as well as nutritional data provided by food growers and manufacturers about their products. We believe the information on this blog to be accurate. However, we are not responsible for typographical or other errors. Nutrition information for recipes is calculated by Living Cookbook based on the ingredients in each recipe based on statistical averages. Nutrition may vary based on methods of preparation, origin and freshness of ingredients, and other factors.

This blog is not a substitute for the services of a trained health professional. Although we provide nutritional information, the information on this blog is for informational purposes only. No information offered by or through this blog shall be construed as or understood to be medical advice or care. None of the information on this blog should be used to diagnose or treat any health problem or disease. Consult with a health care provider before taking any product or using any information on this blog. Please discuss any concerns with your health care provider.

26 thoughts on “Seeking the Proper Level of Selenium

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