After potassium, Magnesium is the second­most abundant intracellular cation in the body. The adult human body contains approximately 20 to 28 g of magnesium, of which approximately 60% is found in bone, 26% in muscle, and the remainder in soft tissues and body fluids.

Functions

Magnesium plays a role in neuromuscular transmission and activity, working in concert with and against the effects of calcium, depending on the system involved. High magnesium intakes are associated with greater bone density.

Food Sources and Intakes
Magnesium is abundant in many foods. Good sources are seeds, nuts, legumes, and milled cereal grains, as well as dark green vegetables, because magnesium is an essential constituent of chlorophyll. Milk is a moderately good source of magnesium, especially because milk and other dairy products are so widely consumed. Magnesium is lost during the processing of foods such as sugar; after refining wheat cereals, it is not generally replaced as enrichment.

Deficiency
Although rare, severe magnesium deficiency symptoms include tremors, muscle spasms, personality changes, anorexia, nausea, and vomiting. Tetany, myoclonic jerks, athetoid movements, convulsions, and coma have also been . Hypocalcemia and hypokalemia typically occur first, combined with impairment of the individual’s responsiveness to PTH and sodium retention.

 
DRIs
Infants, AIs:    30­-75 mg/day, depending on age
Young children, RDAs:      80­130 mg/day, depending on age
Older children and adolescents, RDAs:   240­-410 mg/day, depending on age and gender
Adults:    310-­400 mg/day, depending on age and gender
Pregnant:   350­-400 mg/day, depending on age
Lactating:     310-­360 mg/day, depending on age