Selenium is a trace element closely tied with vitamin E which prevents the breakdown of fats and certain chemicals. Selenium has been shown to be a factor in contracting Keshan disease, and selenium defiency may also affect muscle discomfort and weakness. In areas where selenium levels are low, cancer rates and deaths from high blood pressure are both greater.

Although excessive amounts of selenium have never been observed in humans, in animals it causes stiffness, lameness, hairloss, blindness, and even death.

References:

• National Research Council. Recommended Dietary Allowances, 10th Edition. Washington: 1989.
• Brody, Jane. Jane Brody's Nutrition Book. Bantam Books. 1987.