1, 4 The amount reabsorbed can vary, however, from nearly zero to 99.5% depending on the individual's magnesium balance. To maintain homeostasis, the nephrons normally reabsorb more than 96% of the filtered magnesium. 3, 6 Ionised and complexed magnesium are freely filtered at the glomerulus (70% of circulating magnesium).
There is a circadian excretory rhythm with more magnesium excretion occurring at night. The kidney's handling of magnesium is more complicated. Approximately 1 mmol is lost in gastrointestinal secretions daily. 4Absorption can range from 24% of ingested magnesium in magnesium replete states to 76% in deficient states.
The main site of absorption is the small intestine with smaller amounts absorbed in the colon. Homeostasis depends on the balance between intestinal absorption and renal excretion, with kidney tubules having primary control. Under normal conditions the body maintains constant circulating concentrations of magnesium in the blood.
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