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Magnesium plays a role in over 300 enzymatic reactions within the body, including the metabolism of food, synthesis of fatty acids and proteins, and the transmission of nerve impulses.

The human body contains around 25 gram (g) of magnesium, 50 to 60 percent of which is stored in the skeletal system. The rest is present in muscle, soft tissues, and bodily fluids.

This MNT Knowledge Center feature is part of a collection of articles on the health benefits of key vitamins and minerals.

It looks at the recommended intake of magnesium, its effects on health, dietary sources, and possible health risks.

Fast facts on magnesium

Here are some key points about magnesium. More detail and supporting information is in the main article.

  • Magnesium is vital for the proper functioning of hundreds of enzymes.
  • Consuming adequate magnesium might help reduce premenstrual symptoms.
  • Sunflower seeds, almonds, and shrimp are some of the foods high in magnesium.
  • Magnesium supplements can interact with different drugs, so it is best to check with a doctor before taking them.

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Spinach is a good source of magnesium.

Magnesium is one of seven essential macrominerals.

These are minerals that need to be consumed in relatively large amounts, at least 100 milligrams (mg) per day.

An adequate intake can help prevent problems with bones, the cardiovascular system, diabetes, and other functions.

The following health benefits have been associated with magnesium.

1. Bone health

Magnesium is important for bone formation. It helps assimilate calcium into the bone and plays a role in activating vitamin D in the kidneys. Vitamin D is also essential for healthy bones.

Optimal magnesium intake is associated with greater bone density, improved bone crystal formation, and a lower risk of osteoporosis in women after menopause.

2. Calcium absorption

Calcium and magnesium are important for maintaining bone health and preventing osteoporosis.

Without magnesium, a high intake of calcium can increase the risk of arterial calcification and cardiovascular disease, as well as kidney stones.

Anyone who is taking calcium supplements should also take magnesium to ensure their calcium intake is properly metabolized.

3. Diabetes

Magnesium plays an important role in carbohydrate and glucose metabolism, so magnesium status can also impact the risk of diabetes.

Several studies have associated a higher intake of magnesium with a lower risk of diabetes.

For every 100 mg per day increase in magnesium intake, up to a point, the risk of developing type 2 diabetes decreases by approximately 15 percent. Low magnesium levels were linked to impaired insulin secretion and lower insulin sensitivity.

In most of these studies, the magnesium intake was from dietary sources. However, other studies have shown improvement in insulin sensitivity with a magnesium supplement intake of between 300 and 365 mg per day.

According to the National Institutes of Health (NIH), the American Diabetes Association note that further evidence is needed before magnesium can be routinely used for glycemic control in patients with diabetes.

4. Heart health

Magnesium is necessary to maintain the health of muscles, including the heart, and for the transmission of electrical signals in the body.

Adequate magnesium intake has been associated with a lower risk of:

In the Framingham Heart Study, people with the highest intake of magnesium were found to have a 58 percent lower chance of coronary artery calcification and a 34 percent lower chance of abdominal artery calcification.

Patients who receive magnesium soon after a heart attack have a lower risk of mortality. Magnesium is sometimes used as part of the treatment for congestive heart failure (CHF), to reduce the risk of arrhythmia, or abnormal heart rhythm.

A daily intake of 365 mg of magnesium a day has been shown to improve lipid profiles.

The NIH cite findings "significantly" associating higher magnesium levels in the blood with a lower risk of cardiovascular disease and of ischemic heart disease resulting from a low blood supply to the heart. They also note that higher magnesium levels may lower the risk of stroke.

However, they point out that taking magnesium supplements lowers blood pressure "to only a small extent."

The NIH call for a large, well-designed investigation to understand how magnesium from the diet or from supplements might help protect the heart.

5. Migraine headaches

Small studies have suggested that magnesium therapy may help prevent or relieve headaches, but the amount likely to be needed to make a difference is high. It should only be administered by a health professional.

6. Premenstrual syndrome

Ensuring an adequate intake of magnesium, especially combined with vitamin B6, may help relieve symptoms of premenstrual syndrome (PMS), such as bloating, insomnia, leg swelling, weight gain, and breast tenderness.

7. Relieving anxiety

Reductions in magnesium levels, or changes in the way that it is processed, have been linked to increased levels of anxiety.

This appears to related activity in the hypothalamic-pituitary-adrenal (HPA) axis, a set of three glands that control a person's reaction to stress.

Research has shown that a low-magnesium diet may alter the types of bacteria present in the gut, and this may impact anxiety-based behavior.

Magnesium deficiency is rare, but it may affect older people. It can result from excess consumption of alcohol, some health conditions, such as a gastrointestinal disorder, and the use of some medications.

Symptoms include:

  • loss of appetite
  • nausea and vomiting
  • fatigue and weakness

More advanced symptoms include:

  • numbness and tingling
  • muscle cramps
  • seizures
  • personality changes
  • heart rhythm changes and spasms

Deficiency is linked to insulin resistance, metabolic syndrome, coronary heart disease, and osteoporosis. It can lead to low calcium or low potassium levels in the blood.

The Recommended Daily Allowance (RDA) for magnesium depends on age and gender.

The NIH recommend the following intake of magnesium:

  • From 1 to 3 years of age: 80 mg a day
  • From 4 to 8 years: 130 mg a day
  • from 9 to 13 years: 240 mg a day

From 14 years, the requirements are different for men and women.

  • Males aged 14 to 18 years: 410 mg a day
  • Males aged 19 years and over: 400 to 420 mg a day
  • Females aged 14 to 18 years: 360 mg a day
  • Females aged 19 years and over: 310 to 320 mg a day
  • During pregnancy: 350 to 400 mg a day
  • During breast feeding: 310 to 360 mg a day

How well do we absorb magnesium?

The "bioavailability" of a nutrient is the degree to which it is absorbed and retained in the body for use.

Magnesium has a medium level bioavailability. It is mainly absorbed in the small intestine.

How effective absorption is depends on:

  • the amount of magnesium in the diet
  • the health of the gastrointestinal tract
  • the overall magnesium status of a person
  • the diet as a whole

The best sources of magnesium are nuts and seeds, dark green vegetables, whole grains, and legumes. Magnesium is also added to some breakfast cereals and other fortified foods.

Here are some good sources of magnesium:

  • Sunflower seeds, dry roasted, 1 cup: 512 mg
  • Almonds, dry-roasted, 1 cup: 420 mg
  • Sesame seeds, roasted whole, 1 ounce: 101 mg
  • Spinach, boiled, 1 cup: 78 mg
  • Cashews, dry-roasted, 1 ounce: 74 mg
  • Shredded wheat cereal, two large biscuits: 61 mg
  • Soymilk, plain, 1 cup: 61 mg
  • Black beans, cooked, 1 cup: 120 mg
  • Oatmeal, cooked, 1 cup: 58 mg
  • Broccoli, cooked, 1 cup: 51 mg
  • Edamame, shelled, cooked, 1 cup: 100 mg
  • Peanut butter, smooth, 2 tablespoons: 49 mg
  • Shrimp, raw, 4 ounces: 48 mg
  • Black-eyed peas, cooked, 1 cup: 92 mg
  • Brown rice, cooked, 1 cup: 84 mg
  • Kidney beans, canned, 1 cup: 70 mg
  • Cow's milk, whole, 1 cup: 33 mg
  • Banana, one medium: 33 mg
  • Bread, whole-wheat, one slice: 23 mg

Magnesium is lost as wheat is refined, so it is best to choose cereals and bread products made with whole grains. Most common fruits, meat, and fish, are low in magnesium.

An overdose of magnesium through dietary sources is unlikely, because any excess magnesium that is consumed in food will be eliminated in the urine.

However, a high intake of magnesium from supplements can lead to gastrointestinal problems, such as diarrhea, nausea, and cramping.

Very large doses can cause kidney problems, low blood pressure, urine retention, nausea and vomiting, depression and lethargy, a loss of central nervous system (CNS) control, cardiac arrest, and possibly death.

Anyone with a kidney disorder should not take magnesium supplements, unless their doctor advises it.

Magnesium supplementation may also give rise to some drug interactions.

Medications that may interact with magnesium include:

  • Dabrafenib
  • Digoxin
  • Eltrombopag
  • Elvitegravir
  • Gefitinib
  • Ketoconazole
  • Ledipasvir
  • Levomethadyl
  • Licorice
  • Mycophenolate Mofetil
  • Mycophenolic acid
  • Pazopanib
  • Phenytoin
  • Quinine
  • Raltegravir
  • Rilpivirine
  • Vismodegib

Should I take supplements?

Magnesium supplements are available to purchase online, but it is best to obtain any vitamin or mineral through food, because nutrients work better when combined with other nutrients.

Many vitamins, minerals, and phytonutrients work synergistically. This means that taking them together brings more benefit for health than consuming them separately.

It is better to focus on a healthful, balanced diet to meet daily requirements for magnesium, and to use supplements as a backup, but under medical supervision.