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Food-Info.net > Minerals Magnesium (Mg) |
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Cocoa powder |
Sunflower seeds |
Pumpkin seeds |
Bran |
Nuts |
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Peanut butter |
Wheat flakes |
Popcorn |
Spinach |
Wholegrain bread |
The European Union RDA for the general population is set at 300 mg/day.
In general, the intake of magnesium depends on the age of the person. Pregnant women need a higher intake for the developing baby.
Vitamin D and calcium The active form of vitamin D (1,25-dihydroxycholecalciferol, calcitriol) may increase the intestinal absorption of magnesium to a small extent. Inadequate blood magnesium levels are known to result in low blood levels, resistance to parathyroid hormone (PTH), and resistance to some of the effects of vitamin D.
Zinc High doses of zinc in supplement form appear to interfere with the absorption of magnesium.
Magnesium is involved in over 300 essential metabolic reactions.
Energy production
The metabolism of carbohydrates and fats to produce energy require numerous magnesium-dependent chemical reactions. Magnesium is required by the adenosine triphosphate (ATP) synthesizing protein in mitochondria. ATP, the molecule that provides energy for almost all metabolic processes, exists primarily as a complex with magnesium (MgATP).
Synthesis of essential molecules
Magnesium is required at a number of steps during the synthesis of nucleic acids (DNA and RNA) and proteins. A number of enzymes participating in the synthesis of carbohydrates and lipids require magnesium for their activity. Glutathione, an important antioxidant, requires magnesium for its synthesis.
Structural roles
Magnesium plays a structural role in bone, cell membranes, and chromosomes.
Ion transport across cell membranes
Magnesium is required for the active transport of ions like potassium and calcium across cell membranes. Through its role in ion transport systems, magnesium affects the conduction of nerve impulses, muscle contraction, and the normal rhythm of the heart.
Cell signalling
Cell signalling requires MgATP for the phosphorylation of proteins and the formation of the cell signalling molecule, cyclic adenosine monophosphate (cAMP). cAMP is involved in many processes, including the secretion of parathyroid hormone (PTH) from the parathyroid glands.
Cell migration
Calcium and magnesium levels in the fluid surrounding cells affect the migration of a number of different cell types. Such effects on cell migration may be important in wound healing.
For many people, dietary intake may not be high enough to promote an optimal magnesium status, which may be protective against disorders such as cardiovascular disease and immune dysfunction.
The health status of the digestive system and the kidneys significantly influences magnesium status. Magnesium is absorbed in the intestines and then transported through the blood to cells and tissues. Approximately one-third to one-half of dietary magnesium is absorbed into the body. Gastrointestinal disorders that impair absorption such as Crohn's disease can limit the body's ability to absorb magnesium. These disorders can deplete the body's stores of magnesium and in extreme cases may result in magnesium deficiency.
Healthy kidneys are able to limit urinary excretion of magnesium to compensate for low dietary intake. However, excessive loss of magnesium in urine can be a side effect of some medications and can also occur in cases of poorly controlled diabetes and alcohol abuse.
Adverse effects have not been identified from magnesium occurring naturally in food. However, adverse effects from excess magnesium have been observed with intakes of various magnesium salts (supplemental magnesium). The initial symptom of excess magnesium supplementation is diarrhoea--a well-known side effect of magnesium that is used therapeutically as a laxative.
Individuals with impaired kidney function are at higher risk for adverse effects from magnesium supplementation, and symptoms of magnesium toxicity have occurred in people with impaired kidney function taking moderate doses of magnesium-containing laxatives or antacids. Elevated serum levels of magnesium (hypermagnesemia) may result in a fall in blood pressure (hypotension). Some of the later effects of magnesium toxicity, such as lethargy, confusion, disturbances in normal cardiac rhythm, and deterioration of kidney function, are related to severe hypotension. As hypermagnesemia progresses, muscle weakness and difficulty breathing may occur. Severe hypermagnesemia may result in cardiac arrest
Magnesium homeostasis is regulated by a fine balance between gastrointestinal absorption and renal excretion.
Magnesium is absorbed homogeneously throughout the small intestine, which is vitamin D dependent. The percentage of magnesium absorbed is inversely proportional to the amount of this cation in the diet.
The other major site of regulation of magnesium homeostasis is the kidney. The excretion of magnesium varies between 3% to 25% of the amount filtered in the glomeruli, depending on the serum level of magnesium. Magnesium restricted diet causes an increase in magnesium reabsorption in the loop of Henle before the occurrence of a detectable change in serum concentration. The most important mechanism of regulation of magnesium excretion in the kidney is changes in the reabsorption of the filtered magnesium in the loop of Henle and the proximal tubule. Magnesium reabsorption occurs mainly in the loop of Henle (65%), and in the proximal tubule (20%-30%) and a smaller percentage of magnesium is reabsorbed in the distal tubule (2%-5%). The endocrine system might also have a role in the regulation of magnesium homeostasis. Different studies have shown that aldosterone might either increase or have an effect on urinary magnesium excretion
Ursel, A. : Natural care Vitamins & Minerals Handbook. Dorling Kindersley, London, 2001. ISBN 80-89179-01-0
Dutch Nutrition Centre : www.voedingscentrum.nl/
Images adapted from here.
www.mgwater.com/bar_dayan.shtml
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