Selenium: RDA and upper tolerable limit

http://umm.edu/health/medical/altmed/supplement/selenium

Recommended dietary allowance of selenium for Adult
19 and older: 55 mcg

As a supplement

Some studies have used 200 mcg per day for some conditions. But evidence suggests that taking that amount over a long period of time could increase your risk of developing diabetes. Talk to your doctor before taking more than the recommended daily allowance.

Precautions

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Talk to your doctor before taking more than the recommended daily allowance of selenium.

Although some studies have used doses of 200 mcg, there is some evidence that this amount could increase your risk for diabetes.

DO NOT exceed the upper tolerable limit of 400 mcg. Remember that you may also get some selenium in the foods you eat.