Everything You Need To Know About Magnesium


Welcome to my blog entitled ‘Everything You Need To Know About Magnesium“.

The human body contains around 25 g of Mg (1).

Why Is Mg So Important?

Mg is necessary for the functioning of over 300 enzymes in human, with 90% of total body mg being contained in the muscles and bones, 90% of which is bound and with only 10% being free. (1)

Some of the main functions of mg include (1):

  • The maintenance of ionic gradients (keeping intracellular sodium and calcium low and potassium high).
  • Cellular and tissue integrity.
  • Mitochondrial oxidative phosphorylation (energy production).
  • DNA, RNA and protein synthesis and integrity.

Magnesium (Mg) Deficiency

There are two types of nutrient deficiencies:

  1. Frank deficiencies (such as scurvy from ascorbic acid deficiency or goitre from iodine deficiency).
  2. Subclinical deficiencies (a clinically silent reduction in physiological, cellular and/or biochemical functions).

It is the latter that is most concerning as it is hard to diagnose and predisposes to numerous chronic diseases. And while both result in negative health consequences, the former has obvious symptoms (hence frank deficiency), whereas the latter may have negative or variable health effects that are not so apparent (eg, vascular calcification).

The evidence in the literature suggests that subclinical mg deficiency is rampant and one of the leading causes of chronic diseases including cardiovascular disease and early mortality around the globe, and should be considered a public health crisis (1)

Reliable Ways To Test Magnesium

Mg deficiency is extremely hard to diagnose since symptoms are generally non-specific, there are numerous contributing factors, and there is no simple easy way to diagnose mg deficiency.

  • Thoren’s intravenous mg load test (16 hours)

Retention of Mg load (intravenous or oral) after its administration is likely the best indicator of mg deficiency. However, the retention test assumes normal kidney function for intravenous mg loads and normal gastrointestinal and renal function for oral load tests and is cumbersome and invasive.

Unreliable Ways To Test For A Magnesium Deficiency

  • Hair mg content (one study concluded: ‘mg hair concentration may be an easier, cheaper and less invasive indicator of body magnesium depletion’).
  • Bone mg (mg depletion in the coccyx may indicate magnesium deficiency).
  • Ratio of ionised magnesium to total mg (serum or plasma).
  • Lymphocyte magnesium.
  • Urinary or faecal mg excretion (low or high levels may
    indicate deficiency).
  • Urinary fractional mg excretion >4% (some authors
    have suggested >2% in those with normal kidney function).
  • Total erythrocyte mg levels
  • Total serum mg levels.

Top Signs Of A Magnesium Deficiency

  • Anxiety
  • Cramps
  • Irritability
  • Muscular weakness
  • Tinnitus
  • Vitamin D resistance
  • Arrhythmia
  • Depression
  • Osteoporosis

What Causes Magnesium Deficiency?

Numerous factors can lead to deficiency, including:

  • Kidney failure.
  • Alcohol consumption.
  • Malabsorption issues (magnesium is absorbed in the small intestine and in the colon; thus, patients with intestinal or colon damage such as Crohn’s disease, irritable bowel syndrome, coeliac disease, gastroenteritis, ulcerative colitis, may have magnesium deficiency).
  • Supplementing with calcium can lead to magnesium deficiency due to competitive inhibition for absorption.
  • Over supplementing with vitamin D may lead to mg deficiency via excessive calcium absorption.

A meta-analysis of 13 studies in almost 5500 patients found that mg levels were significantly lower in patients with metabolic syndrome versus controls. (1)

How Much Magnesium Should I Supplement?

One group of authors concluded: ‘When mg substitution is started, the minimum dose to be applied is 600 mg mg per day.The therapy should proceed for more than one month, and then continue with a dose that holds the serum value not lower than 0.9mmol/L mg’. The authors noted that using a cut-off of 0.75mmol/L for mg deficiency misses 50% of those with true mg deficiency. (1)

Conclusions: Everything You Need To Know About Magnesium

Subclinical magnesium deficiency is a common and 19. under-recognised problem throughout the world.

Importantly, subclinical magnesium deficiency does not manifest as clinically apparent symptoms and thus is not easily recognised by the clinician.

Despite this fact, subclinical magnesium deficiency likely leads to hypertension, arrhythmias, arterial calcifications, atherosclerosis, heart failure and an increased risk for thrombosis (1).

This suggests that subclinical magnesium deficiency is a principal, yet under-recognised, driver of cardiovascular disease (1).


  1. DiNicolantonio JJ, O’Keefe JH, Wilson W. Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open Heart 2018;5:e000668 (click here)
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