Role in the body
Symptoms of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures, personality changes, abnormal heart rhythms, and coronary spasms can occur. Severe magnesium deficiency can result in hypocalcemia or hypokalemia (low serum calcium or potassium levels, respectively) because mineral homeostasis is disrupted.
Forms of administration
Magnesium may be taken as an oral supplement but may not be well absorbed. Other forms of magnesium administration include transdermal magnesium and intramuscular magnesium injections.
Magnesium is hypotonic. Administration can cause water to flow into cells in the local area where it is applied, which can cause a temporary stinging sensation.
Chronic Fatigue Syndrome
A randomised, double-blind, placebo-controlled trial of 20 CFS patients found that CFS had lower red blood cell magnesium than healthy controls. Patients treated with intramuscular magnesium sulphate for six weeks had higher self-reported energy levels, better emotional state and less pain on the Nottingham health profile when compared to placebo. 
A 2014 study found magnesium transporter issues were linked to chronic Epstein-Barr infection, decreased Natural killer cell function, and neoplasia (sometimes-cancerous growths).  This disorder, termed 'X-MEN' (for X-linked, EBV, and neoplasia) was identified as a recessive, X-linked disorder that would therefore be many times more common in men. Due to magnesium's role as a 'second messenger', this magnesium transporter disorder also would result in a primary immunodeficiency that would worsen with age.  Patients also have impaired T-cell activation and decreased natural killer (NK) cell function due to a decreased expression of "the NK stimulatory receptor 'natural-killer group 2, member D' (NKG2D)." Although T-cells are affected, there is no direct evidence of B-cell effects in X-MEN disease.
Since chronic Epstein-Barr virus infection has been associated with chronic fatigue syndrome, this error in magnesium transport may be worth considering in male patients, especially with slow onset and history of childhood infection.
Mast cell activation disorder
- I.M., Cox; M.J., Campbell; D., Dowson (1991), "Red blood cell magnesium and chronic fatigue syndrome", The Lancet, PMID 1672392, doi:10.1016/0140-6736(91)91371-Z
- Li, F.-Y.; Chaigne-Delalande, B; Su, H; Matthews, H; Lenardo, M.J. (2014), "XMEN disease: a new primary immunodeficiency affecting Mg2+ regulation of immunity against Epstein-Barr virus.", Blood, doi:10.1182/blood-2013-11-538686
- Ravell, J; Chaigne-Delalande, B; Lenardo, M (2014), "XMEN disease: a combined immune deficiency with magnesium defect.", Current Opinion in Pediatrics, doi:10.1097/MOP.0000000000000156