Magnesium

Similar to calcium, magnesium is found as a divalent cation (Ca2+) within the body.¹ More than half of the magnesium found is within bone tissue, and an adult body contains anywhere between 20-28 grams.¹

Absorption: Magnesium is absorbed in different areas within the small intestine. It is minimally absorbed in the colon unless the small intestine’s function is reduced.¹ Within the ileum, magnesium uses a saturable process that relies on a channel protein known as TRPM6.¹ Paracellular diffusion is used when the luminal concentration of magnesium is high compared to the saturable process.¹ To export magnesium from blood, an energy-dependent process is used to exchange sodium for magnesium.¹

Magnesium absorption is dependent on a variety of factors and ranges between 25-60%.¹ Low levels of magnesium and the presence of vitamin D increase its absorption. A diet high in magnesium or calcium, and the presence of phosphates, phytates, and fatty acids lower its absorption. Calcium may compete with magnesium, and fatty acids create soaps that prevent absorption.¹

Circulation and Excretion: 60% of magnesium is found within bone; the remaining portions are found within extracellular fluid (1%) and soft tissue (39%).¹ Within circulation, magnesium can be bound to proteins or anions (phosphates, citrates, etc).¹ Unabsorbed magnesium is excreted as feces and circulating magnesium is reabsorbed by the kidneys after entering ultrafiltrate.¹

Functions:  

Bone Structure - Magnesium makes up a portion of the crystal lattice of bone and is also found on the surface of bone.¹

ATP Structure and Function - Magnesium bonds with negatively charged oxygen on ATP’s phosphate tail which stabilizes the molecule and assists reactions.¹

Enzyme Reactions - Magnesium serves as a cofactor or as a component in over 300 enzymatic reactions, including enzymes used in glycolysis such as hexokinase, glucokinase, and phosphofructokinase (PFK).¹ Cholesterol synthesis, B-oxidation, DNA replication, RNA transcription, protein synthesis, and cAMP synthesis are processes that require magnesium.¹ 

Active Transport of Nutrients - Magnesium serves as a cofactor for ion channels and pumps that actively transport ions such as calcium and potassium.² This impacts nerve impulses, muscle contractions, and heart rhythm.²

Hormonal Signals - Magnesium is used to stimulate the parathyroid hormone which is responsible for kidney, bone, and intestinal hormonal responses.¹ The conversion of vitamin D into 25-hydroxycholecalciferol in the liver requires magnesium for enzyme 25-hydroxylase.¹ 24-hydroxylase (converts 25-hydroxycholecalciferol to the inactive form of vitamin D) and 1α-hydroxylase (converts 25-hydroxycholecalciferol to the active form of vitamin D) within renal cells also relies on magnesium.¹

Anti-Inflammatory Role - Hypoxia (lack of oxygen) can arise from low magnesium levels which results in the production of free radicals and cytokines (interleukins and interferon) that produce an inflammatory response.¹

Role in Diseases - Low magnesium is linked to a variety of diseases such as type II diabetes, ischemic heart disease, cancers, Alzheimer’s disease, and metabolic syndromes.¹ In clinical trials, supplementation of magnesium in individuals with high blood pressure and type II diabetes has demonstrated lower blood pressure, increased insulin sensitivity, and reduced blood glucose.¹ However, magnesium supplementation can potentially cause cardiovascular issues and some studies produce inconclusive results.¹

Dietary Reference Intake (DRI) - The recommended dietary allowance (RDA) for young adult men (19-30 years old) is 400mg, and for older adult men (31-51+ years old) is 420 mg.² The RDA for young adult women (19-30 years old) is 310 mg, and for older adult women (31-51+ years old) is 320 mg.²

Deficiency - Magnesium deficiency is uncommon by itself but can present due to complications from excessive vomiting and diarrhea, alcoholism, endocrine diseases, kidney disease, and malnutrition. Diuretics can also cause a deficiency of magnesium if excessive. Deficiency results in abnormal parathyroid hormone release and protein pump ability to regulate sodium and potassium.¹ Low calcium may also occur. Symptoms range from anorexia to muscle spasms, tremors, and tachycardia.¹

Toxicity - Excessive magnesium intake, likely through supplementation, can possibly result in renal damage.² It can cause varying degrees of symptoms, ranging from vomiting and lethargy in the beginning stages to difficulty breathing and cardiac arrest in critical stages.²

Dietary Sources of Magnesium

Magnesium is found in a variety of foods, including nuts/seeds, grains, legumes, vegetables, and dairy products. Magnesium is found in chlorophyll (the green pigment of plants), and green-leaf vegetables are known to contain magnesium.¹ It is also fortified into refined grain or wheat products. Boiling foods can reduce magnesium content as it is a water-soluble mineral.¹

Examples of foods containing magnesium include:

Grains/Nuts/Seeds - Pumpkin seeds, chia seeds, cereal, peanuts, cashews 

Vegetables - spinach, potato, peas, avocado

Legumes - black beans, kidney beans

Dairy - yogurt, milk

Meat - chicken, beef, pork 

Fruit - Banana, raisins, apple

Source(s):

1. Denise M Medeiros and Robert E.C. Wildman, Advanced Human Nutrition, 4th ed. (Burlington, MA: Jones & Bartlett, 2019).

2. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/