Some of the key functions of manganese include:

1. Bone development: Manganese plays a crucial role in the development of healthy bones. It helps in the formation of connective tissues, collagen production, and bone mineralization.
2. Metabolism: Manganese is involved in the metabolism of carbohydrates, amino acids, and cholesterol. It also plays a role in the synthesis of fatty acids and the breakdown of carbohydrates for energy.
3. Antioxidant activity: Manganese is a cofactor for several enzymes that act as antioxidants in the body. It helps to neutralize free radicals and protect cells from oxidative damage.
4. Blood sugar regulation: Manganese is involved in the production and secretion of insulin, which helps to regulate blood sugar levels.
5. Wound healing: Manganese plays a role in the formation of blood clots and tissue repair, which is important for wound healing.

Manganese is present in a variety of foods, including plant-based and animal-based sources. Here are some of the main sources of manganese:

1. Whole grains: Brown rice, oatmeal, quinoa, and whole wheat bread are all good sources of manganese.
2. Nuts and seeds: Almonds, hazelnuts, pecans, walnuts, sunflower seeds, and pumpkin seeds are all high in manganese.
3. Legumes: Chickpeas, lentils, navy beans, pinto beans, and soybeans are all good sources of manganese.
4. Vegetables: Spinach, sweet potatoes, green beans, carrots, and peas all contain manganese.
5. Fruits: Pineapple, raspberries, strawberries, and blueberries all contain manganese.
6. Seafood: Clams, mussels, and crayfish are good sources of manganese.
7. Tea: Black tea and green tea both contain small amounts of manganese.

Manganese deficiency is rare in humans, but it may occur due to several causes, including:

1. Inadequate dietary intake: A diet that is low in manganese-rich foods can lead to deficiency.
2. Malabsorption: Certain conditions such as celiac disease, Crohn’s disease, and ulcerative colitis can interfere with the absorption of manganese from the digestive system, leading to deficiency.
3. Liver disease: Liver damage can impair the metabolism of manganese and result in lower levels of the mineral in the body.
4. Parenteral nutrition: Intravenous feeding without manganese supplementation can lead to a deficiency.
5. Antacids: Overuse of antacids can interfere with the absorption of manganese and lead to deficiency.
6. Chronic alcoholism: Chronic alcohol consumption can increase the excretion of manganese and reduce its absorption, leading to deficiency.
7. Medications: Certain medications such as antipsychotics, anticonvulsants, and some antibiotics can interfere with manganese absorption.

The symptoms of manganese deficiency may include:

1. Impaired growth and reproductive functions
2. Weakness and fatigue
3. Abnormal glucose metabolism leading to high blood sugar levels
4. Skeletal abnormalities
5. Skin rash
6. Impaired vision and hearing
7. Changes in hair and nails
8. Nausea and vomiting

However, manganese deficiency is rare in humans and usually occurs only in cases of severe malnutrition or certain medical conditions.