Last reviewed 01/2018

Magnesium is an essential component of soft tissues and bone. It is required for the normal functioning of muscle and nervous tissue. It exerts effects similar to those of calcium and acts directly at the motor endplate. It is an important activator ion participating in the function of many enzymes involved in phosphate transfer reactions.

Magnesium is found in:

  • bone:
    • 50% of the total
    • insoluble

  • cells:
    • 45% of the total
    • a cation required as a co-factor for ATP, etc.

  • the extracellular fluid:
    • 5% of the total

The normal plasma range is 0.75 to 1.0 mmol/l. It is abundant in the normal diet and is eliminated in the urine and faeces.

Changes in plasma magnesium usually induce changes in calcium. Hypomagnesaemia impairs PTH secretion and may also impair end organ response to PTH.