When it comes to vitamins and minerals, more isn't necessarily better. This is particularly true for micronutrients, which your body needs only in small amounts. Selenium is an essential trace mineral required for your body to function properly, but it can be toxic at elevated levels. For this reason, it's crucial to avoid exceeding the recommended daily allowance and to know the signs and symptoms of selenium toxicity.
The recommended daily selenium allowance is 55 micrograms for adults, 60 micrograms if you are pregnant and 70 micrograms for nursing mothers. Levels exceeding this amount, especially from supplements, are not guaranteed to be safe. However, most healthy adults can typically tolerate up to 400 micrograms. Young children, on the other hand, cannot tolerate as much, with the safe upper limit being 90 micrograms for children 1 to 3 years of age.
The amount of selenium recommended per day refers to a combination of dietary and supplemental intake. The average adult following a balanced diet gets enough selenium without the need for supplementation. Therefore, selenium toxicity is almost always related to dietary supplements. Selenium is found in a wide variety of foods, and because you will get at least a portion of your daily intake from your diet, it is recommended that you avoid supplements with amounts exceeding 55 micrograms.
Dietary supplements are not held to the same standards as pharmaceutical medications and, therefore, some manufacturers produce products with an unsafe amount of selenium. Toxicity symptoms can arise within days or weeks of taking supplements with amounts that exceed the recommended intake. The most frequently reported symptoms include gastrointestinal upset, diarrhea and nausea. If it's not caught quickly, you can go on to experience hair loss, fatigue, joint pain and brittle nails.
Although 400 micrograms is the tolerable upper limit for adults, the safety of taking 100 micrograms per day in the form of dietary supplements is not established and could be unsafe if you are getting enough from your diet. Consider that a 3-ounce can of tuna contains nearly 70 micrograms, an ounce of sunflower seeds has 23 micrograms and a cup of oatmeal contains 12 micrograms. It's best to obtain your daily selenium requirement from food. If you must take supplements due to malabsorption issues, consult your physician to help you choose a safe supplementation level.
Janet Renee is a clinical dietitian with a special interest in weight management, sports dietetics, medical nutrition therapy and diet trends. She earned her Master of Science in nutrition from the University of Chicago and has contributed to health and wellness magazines, including Prevention, Self, Shape and Cooking Light.