Manganese acts as an important activator for the metabolism of amino acid glutamine. Without it, the brain could build up an excessive amount of glutamate that is observed to cause numerous symptoms. These include hyperalgesia (increased sensitivity to pain), anxiety, restlessness and ADHD-like symptoms. Besides neurodegenerative conditions, manganese is also responsible for proper bone growth, digestion, and blood sugar homeostasis.
International variability in diet and requirements of manganese: Causes and consequences
Manganese superoxide dismutase in disease.
Those who have a manganese deficiency are more prone to poor bone growth, slow or imparied growth, low fertility, and abnormal metabolism of carbohydrates and fat.