If one of vitamin D’s cofactors could be labeled as most important, magnesium would be it.

The fourth most abundant mineral in the human body, magnesium is crucial to its proper functioning and is involved in more than 300 bodily processes 12 including:

  • muscle and nerve function
  • heart rhythm
  • immune system function
  • blood sugar level regulation
  • blood pressure
  • energy metabolism
  • protein synthesis
  • bone health

Magnesium is also important for proper metabolism of calcium, phosphorus, sodium, potassium, and vitamin D.

Magnesium and vitamin D

Magnesium has been found to influence the body’s utilization of vitamin D in the following ways: Magnesium activates cellular enzymatic activity. In fact, all the enzymes that metabolize vitamin D require it. 34 Low magnesium has been shown to alter, by way of decreasing, production of vitamin D’s active form, 1,25(OH)2D (calcitriol). 5



Magnesium is needed to exert positive influence over the human genome and may be involved in the genetic actions of vitamin D. Magnesium possibly has a role in vitamin D’s effect on the immune system. 6

Animal studies have shown magnesium is also necessary for vitamin D’s beneficial actions on bone. 78

Supplementary and dietary magnesium

Daily needs

Men generally require more magnesium per day than do women. The US Government RDA for magnesium is not sufficient for maintaining adequate magnesium balance within the body, and both men and women may require more than is recommended. 9

Studies reveal the minimal daily requirement for magnesium is around 3 mg/lb (6 mg/kg). So, for a 160 lb (70 kg) adult, this would be about 420 mg. 9

In addition, optimum daily intake is considered to be between 3-5 mg/lb (7-10 mg/kg), equaling somewhere around 490-700 mg. 9

Which form of magnesium?

Supplemental magnesium comes in many different forms, many of which have low absorption and bio-availability, decreasing their effectiveness. How effective a magnesium supplement is can be determined by two things:

  1.  amount of elemental magnesium contained
  2.  bioavailability of the magnesium (determined by its source)

Magnesium oxide is the most common form of magnesium sold, but only about 4% is absorbed, making it ineffective at providing the body’s magnesium needs. 10 One study even found magnesium oxide supplementation “resulted in no differences compared to placebo.” 11

Magnesium taurate, glycinate, citrate, and gluconate have demonstrated higher absorption and bioavailability. 12 Magnesium malate and glycinate are considered by many to be even more effective supplemental forms.

Transdermal magnesium chloride

Gaining in popularity is another form of magnesium, known as transdermal magnesium chloride or magnesium oil. Instead of oral administration, the magnesium chloride is applied to the skin where it is absorbed directly into the cells, bypassing the digestive tract. Due to this, magnesium chloride is said to be the most readily-absorbed form, though there have yet to be any studies performed.

Foods that contain magnesium

 Nuts and seeds are a great source of magnesium.

The following foods are good sources of magnesium, providing anywhere from 64-170 mg per serving:

  • Halibut
  • Spinach
  • Squash
  • Seeds, especially pumpkin and toasted sesame
  • Beans, especially pinto and black
  • Plantain, raw
  • Nuts, especially Brazil nuts, almonds, peanuts

Magnesium deficiency

Magnesium deficiency is epidemic in the United States, with the majority of Americans unknowingly deficient. 913 This can be problematic when optimizing vitamin D levels. In fact, it is common for rising vitamin D levels to bring up symptoms of an underlying magnesium deficiency.

Vitamin D has no known side effects. If one experiences any of the following symptoms due to supplementing with vitamin D – or with sun exposure – a magnesium deficiency is most likely the reason why:

  • irritability or anxiety
  • nausea
  • headaches
  • insomnia
  • fatigue
  • muscle cramps/twitching
  • weakness
  • constipation

How do I know if I am magnesium deficient?

Risk factors

Risk factors for magnesium deficiency include excessive use of alcohol, use of diuretics (water pills), or chronic diarrhea. 141516

Other risk factors are use of blood pressure medication and liver problems. 17181920

Unreliability of blood testing

Magnesium is distributed in the body in the following manner: 21

  • bone: over 60%
  • intracellular:
  • muscle: about 27%
  • other cells: 6-7%
  • extracellular (blood serum): less than 1%

Because very little magnesium resides in the blood, serum levels are an inaccurate index of magnesium status. 222324 In other words, your doctor will not be able to determine magnesium status by testing your serum levels. 25

A low urinary fractional excretion of magnesium (< 2%) may be helpful in diagnosing deficiency. 24 An ionic magnesium test is the most reliable indicator of magnesium status, but is not often performed. 26

Can I get too much magnesium?

Hypermagnesemia (high blood magnesium) is rare due to the kidneys’ rapid response to elevated serum levels. 1527 Main symptoms include lethargy, confusion, arrythmias (slow heart rate), and muscle weakness.

Risk factors for hypermagnesemia include impaired kidney function 15 and/or excessive magnesium intake (example: magnesium laxatives or supplements), which may induce loose stool. 2829 Reduce dosage if this occurs.


Magnesium is safe for the majority of the population. However, those with severe renal insufficiency or who may have a neuromuscular transmission disorder such as Myasthenia Gravis should only use magnesium under a doctor’s supervision. 30

Page last edited: 16 August 2011


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