Manganese is an essential trace mineral that is available only from the diet. It is widely distributed in the earth’s crust at a proportion of 0.085%. Water, plants and animals all contain the mineral in minute quantities.
The body of an adult person contains between 12 and 20 mg manganese with the highest concentrations in the skeleton, liver, kidneys and head. About 4 mg daily is excreted in the faeces.
Whole grains and cereal products are the richest dietary sources of manganese but up to 90% of the mineral is lost during the refining and processing of these foods.
Fruits and vegetables contain lower quantities of the mineral, but are still good sources. Dairy products, meat, fish and poultry are poor sources.
Tea is a good provider of manganese but, at the other end of the scale, drinking water provides negligible amounts.
Little is known about the chemical form of manganese in the diet and its nutritional bioavailability. The extent of absorption depends upon the body’s manganese status. For example, during the third trimester of pregnancy, the rate of absorption of the mineral increases to three times the normal rate. The manganese content of human milk is so low that lactation does not demand any extra intake of the mineral.
In a healthy adult, only between 3 and 5% of manganese is absorbed. Manganese derived from tea is less well absorbed and 2 litres of drinking water per day will provide only 40 mcg, or 2% of the daily requirement. Despite this, body levels remain remarkably constant.
In animals, manganese deficiency causes poor reproductive performance, growth retardation, congenital malformation in the offspring, abnormal bone and cartilage structures and impaired handling of glucose.
Deficiency in humans (observed under experimental conditions) caused decreased levels of cholesterol and clotting proteins as well as reddening of the hair, slowing of fingernail growth and scaly dermatitis.
It is claimed that low body organ levels of manganese have been associated with diabetes, heart disease, schizophrenia, atherosclerosis, myasthenia gravis and rheumatoid arthritis.
Deficiency is usually related to poor diet since food processing and refining causes large-scale losses of the mineral.
Excessive intake of copper may cause manganese deficiency.
Iron is said to be more efficacious in haemoglobin synthesis when there is adequate manganese.
In one case, vitamin K deficiency was not corrected unless a manganese deficiency was first treated.