With magnesium often claimed to be one of the most common nutrient deficiencies, and with so many clients asking about the nutrient I thought I would start creating a ‘master document’ on this amazing nutrient. So over the coming days/week I will add to this article with the aim of covering all necessary questions:

  • What is magnesium?
  • What are the sources of magnesium?
  • How is it absorbed?
  • What functions does it have?
  • What are the symptoms of deficiency?
  • How can we test it?

What Is Magnesium?

Magnesium is the second most abundant intracellular cation, after potassium, and is the fourth most abundant cation in the human body (cation meaning it is negatively charged). This essential mineral is needed for a broad variety of physiological and biochemical functions. As a co-factor in more than 300 enzymatic reactions, which often depend on ATP (energy), magnesium is involved in many biochemical pathways of key importance, including:

  • The degradation of macronutrients (such as fats from our diet)
  • Oxidative phosphorylation (energy production)
  • DNA and protein synthesis
  • Neuro-muscular excitability
  • Regulation of parathyroid hormone secretion

As a physiological calcium channel antagonist, magnesium affects processes that are regulated by intracellular calcium concentration fluxes and is therefore essential for normal neurological and muscular function.

Furthermore, magnesium regulates cell membrane permeability via interactions with phospholipids and affects vessel tone and blood pressure.

More than 99% of the total body magnesium is located in the intracellular space, mainly stored in bone (60-65%), muscle and soft tissues (34-39%), whereas less than 1% is located in the extracellular space. This makes testing for magnesium status very hard (more on this later!).

What Are The Sources Of Magnesium?

Dark leafy greens (e.g kale, spinach), oatmeal, buckwheat, whole grains, chocolate, nuts & seeds, lima beans and molasses, fish, meat, dairy foods.

What Are The Symptoms Of Deficiency?

Cardiac arrhythmia, palpitations, weakness and fatigue, ataxia (loss of full control over body movements), muscle twitches and spasms, low blood levels of calcium and related disorders such as tetany and osteomalacia, low blood levels of potassium, apparent vitamin D deficiency and resistance to standard treatment.

More moderate magnesium deficits may contribute to the following disorders: osteopenia and osteoporosis, soft tissue calcification (such as kidney stones), high blood pressure (hypertension), preeclampsia and eclampsia, migraines, and many aspects of cardiovascular disease.

Recommend Intake

Balance studies suggest a daily Mg2+ requirement of 3.0- 4.5 mg per kg body weight.

Whereas the Institute of Medicine recommends 310-320 mg per day for women and 400-420 mg per day for men as ade- quate, the European Food Safety Authority recently defined an adequate intake of 300 and 350 mg per day for women and men, respectively.


Various factors influence the intestinal uptake of magnesium and are of substantial importance for the supply of the min- eral. Dietary magnesium uptake in the intestine varies within a broad range and depends on dose, the food matrix, and en- hancing and inhibiting factors. Furthermore, several studies have shown that the absorption of magnesium from food supple- ments and pharmaceutical preparations under standard con- ditions is slightly influenced by the type of magnesium salt. Never- theless, an approach that focuses on one or a few aspects is insufficient from a nutritional and medical point of view. To understand the true absorption of magnesium, numerous endogenous and exogenous factors must be considered. Overall, the understanding of magnesium absorption and its influencing factors is still limited, which has been due to methodological limitations.

Intestinal magnesium absorption  occurs pre-dominantly in the small intestine via a paracellular pathway, and smaller amounts are absorbed in the colon, mainly via a transcellular pathway. In humans, magnesium absorption starts approximately 1 h after oral intake, reaches a plateau after 2-2.5 h up to 4-5 h and then declines. At 6 h, the magnesium absorption is approximately 80% complete.

With a daily intake of 370 mg, the absorption rate of magnesium in the intestine ranges from 30-50%. However, the efficiency of magnesium uptake is dependent on the ingested dose. For example, early studies with a low dietary magnesium intake showed that the relative absorption rate can reach 80%, whereas it is reduced to 20% with magnesium surfeits.

(Schuchardt & Hahn, 2017)

Magnesium & Cardiovascular Health

We concluded that high Mg intake is associated with lower risk of major CV risk factors (mainly metabolic syndrome, diabetes and hypertension), stroke and total CVD. Higher levels of circulating Mg are associated with lower risk of CVD, mainly ischemic heart disease and coronary heart disease (Rosique-Esteban et al., 2018).

Magnesium and The Gut Microbiome

Animal studies suggest that magnesium deficiency can contribute to a decline in bacterial diversity.

Testing Magnesium Status

  • Serum magnesium​
  • Red blood cell​ ​magnesium​ (​LabCorp​, ​Quest​)
  • 24-Hour urine magnesium ​(​LabCorp​, Q​ uest​)

Serum magnesium declines in deficiency and rises in toxicity, but it is less sensitive than red blood cell and urine to changes in magnesium status. Red blood cell magnesium may be low when serum is not, and while this could indicate an early deficiency, it could also indicate a deficiency in factors needed for bringing magnesium into cells, such insulin signaling, energy production, and sodium. Urine magnesium will be low in nutritional deficiency, but high in deficiencies caused by urinary loss.

The interpretation of magnesium markers is best facilitated by taking all three measurements. A nutritional magnesium deficiency is likely to produce low values across all three measurements. Low blood values coupled to high urine values reveal urinary magnesium wasting. A large discrepancy between serum and red blood cell magnesium could suggest a problem with magnesium transport.


Jan Philipp Schuchardt & Andreas Hahn (2017) Intestinal Absorption and Factors Influencing Bioavailability of Magnesium – An Update, Current Nutrition & Food Science, 13, 260-278 click here

Rosique-Esteban et al., (2018) Dietary Magnesium and Cardiovascular Disease: A Review with Emphasis in Epidemiological Studies, Nutrients. 2018 Feb 1;10(2) click here

Winther G et al (2015) Dietary magnesium deficiency alters gut microbiota and leads to depressive-like behaviour, Acta Neuropsychiatr. Jun;27(3):168-76 click here

Share this post