Magnesium

Magnesium is an essential mineral involved in numerous biochemical processes, including adenosine triphosphate (ATP) production, cellular signal transduction, DNA, RNA and protein synthesis, and bone formation ^{(1) (2)}. Magnesium also helps regulate blood pressure and enzymes such as those that control intracellular calcium and potassium, and is essential for normal heart functioning ^{(1) (3)}. Dietary magnesium can be found in many foods, and especially in dark green leafy vegetables, nuts, legumes, whole grains, fruits, and fish ⁽⁴⁾.

In dietary supplements, other over-the-counter products, and pharmaceutical preparations, magnesium is combined with another substance such as a salt or acid, and has specific therapeutic uses. Magnesium carbonate, magnesium hydroxide, and magnesium oxide are found in antacid and laxative products. Magnesium citrate is used as a laxative before diagnostic procedures or surgery of the colon. Magnesium chloride, magnesium gluconate, magnesium lactate, and magnesium sulfate are clinically used to treat magnesium deficiency.

Both dietary magnesium and magnesium supplementation have been studied widely for their potential role in chronic ailments such as heart disease and diabetes. Dietary magnesium intake is associated with reduced mortality from cardiovascular disease, especially for women ⁽⁵⁾. It is also associated with reduced risk of sudden cardiac death (SCD), although studies have been mixed and more affirmative for the effect of serum magnesium on SCD ^{(6) (7)}. Dietary magnesium may help reduce the risk of ischemic stroke ⁽⁸⁾, metabolic syndrome ^{(9) (10)}, type 2 diabetes ⁽¹¹⁾ and insulin resistance ⁽¹²⁾, asthma ⁽¹³⁾, and osteoporosis ⁽¹⁾, but study results are conflicting as to whether dietary magnesium can reduce depression ^{(14) (15)}. Other studies also have not linked dietary magnesium with cancer incidence and mortality ⁽¹⁶⁾, or pancreatic cancer risk ⁽¹⁷⁾, but have associated higher intakes with a lower risk for colorectal tumors ⁽¹⁸⁾ and lung cancer ⁽¹⁹⁾. Additional studies are needed to confirm these effects.

Magnesium supplementation has been evaluated for a variety of health conditions. Oral magnesium may increase survival in patients with heart failure ^{(20) (21)}, and improve insulin sensitivity in healthy adults ⁽²²⁾. In a study of overweight individuals, magnesium supplementation resulted in changes in gene expression and other positive effects on metabolic pathways ⁽²³⁾. Some studies have shown a reduction in blood pressure after magnesium supplementation ^{(24) (25)}, but an earlier systematic review suggests the positive findings are due to poor trial design and short duration ⁽²⁶⁾. Also in contrast, data from a large, community-based cohort did not show low serum magnesium to be a risk factor for developing hypertension or cardiovascular disease ⁽²⁷⁾.

Other studies of oral supplements have demonstrated positive effects on bone mass accrual in healthy adolescents with inadequate magnesium intake ⁽²⁸⁾, and suppressed bone turnover in postmenopausal osteoporotic women ⁽²⁹⁾. In adults with asthma, magnesium improved objective measures of airway resistance and subjective measures of asthma control and quality of life ⁽¹³⁾; in pediatric patients with cystic fibrosis, it has improved respiratory muscle strength ⁽³⁰⁾. There is also moderate evidence for its use in migraine headache and prophylaxis ⁽³¹⁾. Although preliminary clinical data have shown mixed results with oral magnesium for premenstrual syndrome ⁽³²⁾, another pilot study has shown it reduces menopausal hot flashes in breast cancer patients ⁽³³⁾, and a systematic review supports its use for leg cramps during pregnancy ⁽³⁴⁾. More and larger studies are needed to elucidate conflicting results and clarify the roles for magnesium supplementation across various health conditions.

Many adults, particularly African-Americans ⁽³⁵⁾ and the elderly ⁽⁹⁾, may not have adequate dietary intakes of magnesium. However, true magnesium deficiency most often occurs with critical illness including cardiac conditions and preeclampsia, as well as gastrointestinal and renal conditions, poorly-controlled diabetes, and alcoholism ⁽³⁾. In addition, certain medications including calcineurin inhibitors ⁽³⁶⁾, high-dose antivirals ⁽³⁷⁾, and the long-term use of proton pump inhibitors ⁽³⁸⁾, as well as some cancer therapy regimens ^{(39) (40)} and surgical procedures ^{(41) (42)}, may also cause hypomagnesemia. If magnesium deficiency is suspected, patients should be evaluated by their treating physician to determine the extent of inadequate intake and its effective management, as well as to avoid potential drug interactions or magnesium toxicity.

Hypermagnesemia is rare and results from failure to excrete magnesium or because of excessive intake. It may especially occur in patients with gastrointestinal or renal dysfunction, and have serious effects such as hypotension, bradycardia, depression of tendon reflexes, and other cardiovascular and neuromuscular manifestations ^{(43) (44)}.