Humans are designed to receive the nutrients they need from food sources. However, many aspects of today's lifestyle are causing us to be magnesium deficient, forcing us to look to some form of supplement in order to obtain larger bioavailable amounts than can easily be obtained from food.

Bioavailable - what does that mean?

Bioavailable means able to be absorbed into the bloodstream / lymph for delivery to the body's cells.

Food and oral supplemental magnesium. Absorbed through intestinal wall via digestive process. This article explores the pros and cons of the many available choices of oral magnesium supplements. Mainly two categories of

Transdermal magnesium chloride. By far the quickest and most effective way to increase our body's levels of this very important mineral. However, many people find this method not as convenient as "popping a pill".

Bodys magnesium retained and available for physiological function: Mg++ stores are tightly regulated via a balanced interplay between intestinal absorption and renal excretion. i.e. Magnesium absorbed via skin or GI tract less the magnesium eliminated by kidneys and GI tract (Sweat losses are generally low, but intense exercise can increase loss). "Mg homeostasis is regulated through the secretion and reabsorption in the kidneys, where about 95% of the excreted, ultrafiltrated Mg is reabsorbed. . . .The ion channel TRPM6 is of particular importance for the absorption from the intestine and the reabsorption of Mg secreted into the primary urine." Rylander, 2014

• Only about 1/3 to 1/2 of oral magnesium is absorbed by the body (even under the best conditions). Magnesium supplied in food or oral supplements is primarily absorbed in the distal end (ileum) of the small intestines and then transported via the blood to cells and tissues. NIH Magnesium Facts Sheet

Magnesium transport into cells

Biomembranes are essentially impermeable to ions and most water-soluble molecules, such as glucose and amino acids. Transport of such ions and molecules across cellular membranes is mediated by transport proteins associated with the underlying bilayer. Because different cell types require different mixtures of low-molecular-weight compounds, the plasma membrane of each cell type contains a specific set of transport proteins that allow only certain ions or molecules to cross.

Magnesium ions react with the cell membranes or are actively brought into the cell as needed.

Magnesium absorption via intestines is affected by many variables

Factors that reduce mg absorption

• High / unphysiological doses of other minerals. Some minerals use and compete for the same transport channels. Eg. copper and zinc salts consumed together will compete for transport across the intestinal wall. An excess of zinc can cause a deficiency of copper and vice versa. A high calcium intake may decrease magnesium absorption

• Partly fermentable fibres (e.g., hemicellulose) / non-fermentable fibres (e.g., cellulose, lignin)

• Concurrent consumption with phytate, oxalate and tannins. Phytate is in improperly prepared nuts, seeds, grains, oxalate is in rhubarb, and tannins in tea. Research suggests that we will absorb approximately 20% more zinc and 60% more magnesium from our food when phytate is absent. Navert & Sandstrom B, 2004

• Single, large doses of Mg++. Since magnesium can not be stored, higher doses than can be utilized are usually excreted.

• Some forms may cause diarrhea, which eliminates magnesium before it can be absorbed. E.g. magnesium oxide, sulphate (Epsom Salts), citrate, carbonate, bicarbonate and magnesium hydroxide ("Milk of Magnesia")

• Stress levels (e.g. due to anxiety or infection);

• GI disorders impair magnesium absorption. E.g. Crohn's disease, IBS;

Enhance mg absorption

• Proteins

• Medium-chain-triglycerides (E.g. in coconut oil)

• Low- or indigestible carbohydrates (e.g., resistant starch, oligosaccharides, inulin, mannitol and lactulose)

• The relative Mg2+ uptake is optimal when the mineral is ingested in multiple low doses throughout the day. A single, large intake of Mg2+ is not as well absorbed.

• Parathyroid hormone (PTH), glucocorticoids (probably by reducing calcium absorption)

Other factors

• Intestinal absorption rate is mainly dependent on person's existing magnesium levels. Mineral absorption increases when there is a mineral shortage, and decreases when mineral levels are high. When intestinal magnesium concentration is low, active transcellular transport prevails, primarily in the distal small intestine and the colon;

• Overall absorption of Mg++ takes place at different rates along the small and large intestines. Duodenum (11%; pH 6), jejunum (22%), ileum (56%, pH 7.4 at terminal end), colon (11%, pH 6.7 at cecum ); Ref. for pH values

• Body has upper limits for absorption rates of minerals to prevent absorption of toxic levels. The body adjusts for specific needs of the body and deficiencies. Magnesium's typical absorbancy rate is 21-27%. Groff et al; Shils et al, 1999. According to Dr. Shealy in his book Holy Water, Sacred Oil: The Fountain of Youth, optimum absorption from the intestines requires a minimum 12 hour transit time. Mg forms which cause diarrhea (Eg. magnesium oxide), speed up the transit time whilst also being eliminated in the stools.

• Circadian plasma magnesium levels vary about 6%. Peak levels occur around 10 a.m and 8 p.m. Wilimzig et al, 1996

• Choose forms of Mg with low ionic bond strength. High bond-strength ionic sources are not well-absorbed (E.g. Magnesium oxide, magnesium carbonate). Magnesium oxide has been shown to have only ~4% absorption rate and is primarily used as a laxative. Firoz & Graber, 2001

• All non-magnesium chloride forms require a sufficiency of hydrogen chloride for their absorption. A problem for many aging people, especially with chronic diseases.

• Whether mg++ salt is organic or inorganic is not of high importance. Some studies demonstrated a slightly higher bioavailability of organic Mg2+ salts compared to inorganic compounds under standardized conditions, whereas other studies did not.

• All non-chelated magnesium salt supplements require a sufficiency of hydrogen chloride in the stomach to ionize (break the ionic bond between) magnesium and whatever it is bonded to. An HCl deficiency is a problem for many older people, especially with chronic diseases. You can ensure a sufficiency of chloride ions for overall digestion by supplementing with betaine HCl.

Forms and location of magnesium in the human body

Total serum magnesium is present in three different states. Published results for each state vary considerably because of different measurement methods. These are the ranges:

55-70% Free, ionized Mg++ (ultrafilterable fraction i e. can pass through kidney filters, of which 95% is reabsorbed);

20-30% Protein-bound (non-ultrafilterable);

5-15% Complexed with anions (e.g. magnesium citrate, bicarbonat

Where is magnesium?

~99% is INTRACELLULAR (inside cells; 1-5% ionized, the rest bound to proteins, anions and ATP [18].) of which:

60-65% is in bone. Mostly in the surface hydroxyapatite, where as a magnesium store, it is accessible in times of serum deficiency;

25-30% in skeletal muscle;

10-15% in non-muscle soft tissues

Only ~1% EXTRACELLULAR

Primarily in serum and red blood cells (RBCs) as free/ionized (most active), bound to protein or complexed with anions;

Reference range for total magnesium concentration in adult blood serum is 0.65-1.05 mmol/L

References:

Dr. H. Dewyne Ashmead's book Amino Acid Chelation in Human and Animal Nutrition

Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnesium Research. 2001; 14: 257-62

Groff JL, Gropper SS. Advanced nutrition and human metabolism, 3rd ed. Belmont, CA: Wadsworth, pp. 371-483.

Jahnen-Dechent W, Ketteler M. Magnesium basics. Clinical Kidney Journal. 2012;5(Suppl 1):i3-i14. doi:10.1093/ndtplus/sfr163..

Magnesium in chronic renal failure

Ragnar Rylander (2014) Bioavailability of Magnesium Salts - A Review. Journal of Pharmacy and Nutrition Sciences, 2014, 4, 57-59 57 pdf

Shils ME, Olsen JA, Shike M, Ross AC (1999) Modern nutrition in health and disease, 9th edition. Baltimore: Williams & Wilkins

Wilimzig C, Latz R, Vierling W, Mutschler E, Trnovec T, Nyulassy S. (1996) Increase in magnesium plasma level after orally administered trimagnesium dicitrate. Eur J Clin Pharmacol 1996; 49: 317-23. Springer link abstract

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