Magnesium is an important mineral involved in many biological processes in the cells of our body. Magnesium is present in bread and cereal products, vegetables, dairy products and meat. The magnesium balance is maintained by the absorption of magnesium in the intestine and bone and the absorption and excretion of magnesium by the kidneys. Blood contains only 1% of the total amount of magnesium in the body. The rest is located in the cells of the bone, the muscles and several other organs.

Numerous complaints can occur due to a low magnesium level in the blood. Examples include nausea, vomiting, sleepiness, fatigue, (muscle) weakness, muscle spasms and muscle cramps, joint pain, a low potassium level in the blood, heart rhythm disturbances and even psychical phenomena and psychiatric diseases. Some people, however, have relatively little complaints of a low magnesium content.

Causes of hypomagnesemia
A low magnesium can be caused by a low intake with the diet, insufficient gastro intestinal uptake or loss through the bowel (sometimes due to chronic diarrhea or certain medications like antacids). In addition, magnesium loss via the urine can also occur due to a problem in the kidneys (renal hypomagnesaemia).

Renal hypomagnesemia
Virtually all of the magnesium in the blood is filtered by the kidney and ends up in the pro-urine, of which our kidneys produce about 180 liters at daily basis. The vast majority of water and substances dissolved therein, including magnesium, are then re-absorbed in the blood by the kidney tubules. There are different processes which, if disturbed, can lead to reduced re-uptake, and hence increased loss of magnesium in the urine. This can have several causes, including certain medications, damage to the renal tubules, as well as genetic defects in the production of proteins that are involved in the re-uptake of magnesium.

Determining the cause
The diagnosis of renal hypomagnesemia is based on an increased magnesium excretion in the urine. This is done by calculating the excretion of urine magnesium in a urine portion. Usually a 24-hour urine sample is collected as well. Depending on the results of the first studies, additional diagnostic studies could be performed. This may include tests to investigate the function of the kidney tubules, or genetic testing. For a description of specific syndromes which may present with renal hypomagnesemia see the links below.
The treatment consists of, where possible, elimination of the cause. If the cause is genetic or the result of chronic damage to the renal tubules, this is often not possible. Usually magnesium supplementation is given, which often have unpleasant side effects such as diarrhea (see text magnesium supplementation) especially because patients require high doses of magnesium to increase the magnesium in their blood and to reduce symptoms.

–    HNF1beta associated kidney disease
–    Familial hypomagnesemia with hypercalciuria and nephrocalcinosis  (FHHNC)
–    Hypomagnesemia with secondary hypocalcemia (HSH)
–    Gitelman syndrome
–    Bartter syndrome
–    Magnesium supplementation