Manganese is a trace element essential to the reproductive system and the maintenance of blood, cartilage, and bone formation. Whole grains and cereals are rich sources of Manganese, along with fruits,vegetables, and tea.

Manganese deficiency has never been proven to have occured in human beings, but among animals it has been shown to cause problems in reproduction, abnormal or slowed growth, birth defects, and irregular bone development. Signs of too much Manganese include blurred speech, involuntary laughing, and tembling hands.

References:

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