Manganese little known and underrated by both doctors and the general public, is an essential mineral important to many enzyme systems in carrying out such functions as energy production, protein metabolism, bone formation, and the synthesis of L-dopamine, cholesterol, and mucopolysaccharides.
The human body contains a total of about 15–20 mg. of manganese. About half of that is in the bones, and the remainder is found in the liver, pancreas, pituitary gland, adrenal glands, and kidneys—the active metabolic organs. Manganese is present in many enzymes in body cells, particularly in the mitochondria (or energy factories) as manganese—containing superoxide dismutase, an antioxidant enzyme.
In the food chain, most manganese is present in plant tissues, mainly in nuts, seeds, and whole grains, but in most vegetables as well, particularly the dark leafy greens. Like that of iron, our absorption of manganese is low; utilization of manganese from the diet has been estimated in the range of 15—30 percent efficiency. Absorption may be influenced by body manganese levels. Alcohol and lecithin cause slight increases in manganese absorption.
Large amounts of calcium and/or phosphorus will interfere with manganese absorption. Heavy milk drinkers, meat eaters, or consumers of soda beverages may therefore need additional manganese. Magnesium, as is found in antacids, may interfere somewhat with manganese absorption. Iron definitely has a seesaw interaction with manganese; too much of either mineral will interfere with absorption of the other. In other words, taking extra manganese can interfere with iron absorption and lead to deficiency, which must then be corrected by taking extra iron. Zinc, cobalt, and soy protein may also interfere with manganese absorption into the blood from the intestines. Manganese can interfere with copper absorption and can decrease copper levels. Optimal absorption of manganese occurs when it is taken in the absence of other minerals or food and in its protein–chelated form.
After absorption, manganese is transported to the liver and then to other organs, such as the kidneys, for storage. A globulin protein called transmangamin carries the manganese molecules in the blood. Manganese is eliminated mainly through the feces after being excreted in the bile. The kidneys clear only a small amount. A manganese blood level (whole blood) can be measured; this level is often low in a person who eats the average American diet.
Sources: Nuts and whole grains are the best sources of manganese. Most animal foods have low levels, though egg yolks are a decent source. Seeds, legumes (peas and beans), and leafy greens, especially spinach, are all good sources of manganese if there is manganese in the soil in which these plants are grown. Alfalfa is high, and black teas and coffee beans have some manganese.
A number of factors, however, can affect dietary manganese levels. As I just implied, food manganese levels may vary greatly because of soil deficiencies; the leafy greens are particularly sensitive to this. Soil mineral losses related to runoff and high-tech farming have created manganese and other mineral depletion problems. Lime added to the soil binds manganese, and, though it may make nice greens, it will result in most foods having a lower manganese content.
Also, though the whole grains, such as barley, whole wheat, millet, and oats, all have good levels of manganese, most of it is in the bran and germ, and these outer parts are often stripped away through milling and refining. Nearly 90 percent of manganese is lost in the refinement of wheat to white flour. Ideally, we should eat whole and unprocessed foods from healthy, balanced soil to get sufficient amounts of manganese and many other minerals.