Magnesium: the pathway in the body · Biomarker & Blood Analysis

This page shows the biochemical pathway behind the laboratory value Magnesium: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Magnesium is a mineral that exists in the body as a doubly charged ion, mostly in bone and inside cells. It forms the active energy carrier together with ATP and acts as a brake in the NMDA receptor. How much stays in the body is regulated mainly by the kidneys.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Magnesium in food → Small intestine Claudin-2, -7, -12 In the small intestine, magnesium passes passively between the gut cells. The passages for this are formed by proteins of the claudin family (claudin-2, -7 and -12). This route follows the gradient and carries most of the absorption. Source 1, 3↑ supplies Most of the magnesium is absorbed here. The route between the cells is passive: it follows the concentration gradient and the electrical voltage across the gut wall. established physiology Source 3, 1
   ⚖ When the balance tips

   too much — If a lot of magnesium is dissolved in the gut, more flows through this route, because it follows the gradient and does not saturate.

   too little — If little magnesium is dissolved, the gradient is shallow and the route between the cells contributes little; the active route through the cells then gains in share.

   established physiology · Source 3

2. Small intestine → Large intestine In the large intestine, the channels TRPM6 and TRPM7 move magnesium into the gut cell. On the blood side, the transporter CNNM4 releases it again, probably in exchange for sodium. This route is adjustable and works even when little arrives. Source 1↑ supplies The route through the cell is active and regulated: TRPM6 and TRPM7 let magnesium in even when little is dissolved in the gut. It is the finely adjustable part of absorption. established physiology Source 1, 3
   ⚖ When the balance tips

   too much — If a lot of magnesium is present, the channels TRPM6 and TRPM7 are fully occupied; this route then does not increase any further.

   too little — If little magnesium is dissolved in the gut, the route through the cell carries a larger share of absorption, because it also works at low concentration.

   established physiology · Source 3, 1

3. Large intestine → Magnesium in the blood TRPM6/7, CNNM4 Only a small share of the body’s magnesium is in the blood. Most of it is in the bones, and a further share in muscles and other tissues. Gut, bone and kidneys keep its level within narrow limits. Source 1↕ both, depending on amount The blood distributes magnesium to cells, bone and kidneys. Its level is kept within narrow limits as gut, bone and kidneys constantly resupply or excrete. established physiology Source 1, 4
   ⚖ When the balance tips

   too much — If magnesium in the blood rises, the kidneys recover less and excrete more; in large amounts it damps the excitability of nerves and muscles.

   too little — If magnesium in the blood falls, the kidneys recover more and the bones resupply. If it falls sharply, the release of parathyroid hormone is slowed, and calcium in the blood also falls more easily.

   established physiology · Source 4, 1

4. Magnesium in the blood → Filtration in kidneys The kidneys filter magnesium from the blood. By far the largest part of it is then recovered along the renal tubules. What is not recovered leaves with the urine. Source 1, 2↓ depletes Filtration removes magnesium from the blood; what the renal tubules do not then recover leaves with the urine. The kidney is thus the site where the body's stock is regulated towards the outside. established physiology Source 2, 1
   ⚖ When the balance tips

   too much — If there is more magnesium in the blood, more of it enters the filtrate; recovery does not keep pace to the same degree, and more leaves with the urine.

   too little — If there is little magnesium in the blood, less is filtered and the tubules recover almost all of it; hardly any is then lost via the urine.

   established physiology · Source 2

5. Filtration in kidneys → Reabsorption Claudin-16/-19, TRPM6 The loop of Henle recovers most of it, between the cells through pores made of claudin-16 and -19. Fine-tuning is done by the distal tubule with the channels TRPM6 and TRPM7. In this way the kidney decides how much magnesium stays in the body. Source 1, 2↑ supplies Recovery decides how much magnesium stays in the body. In the loop of Henle, electrical voltage drives it back between the cells; in the distal tubule, TRPM6 performs the last, adjustable step. established physiology Source 2, 1
   ⚖ When the balance tips

   too much — If magnesium in the blood rises, the calcium sensor CaSR in the loop of Henle detects it; the pores between the cells then let less back, and more is excreted.

   too little — If little magnesium is present, the tubules recover almost all of it. If it falls in the cells of the distal tubule, the potassium channel ROMK releases more potassium into the urine.

   established physiology · Source 2, 4

6. Magnesium in the cell → Mg-ATP ATP, the cell’s energy carrier, forms the Mg-ATP complex with magnesium. It is regarded as the biologically active form; through it, magnesium takes part in several hundred enzyme reactions. Kinases recognise ATP mainly in this form. Source 1, 4↑ supplies Only when bound to magnesium does ATP have the form that kinases and ATPases use. Every step that consumes ATP therefore also depends on magnesium, for example the sodium-potassium pump. established physiology Source 4, 1
   ⚖ When the balance tips

   too much — If more magnesium is present than ATP can bind, the rest stays free or bound to other molecules; no more Mg-ATP then forms.

   too little — If little magnesium is present, more ATP is unbound; enzymes that need Mg-ATP then work more slowly, including the sodium-potassium pump.

   established physiology · Source 4

7. Glucose → Glucose-6-phosphate Hexokinase Hexokinase transfers a phosphate group from ATP to glucose for this. It uses the Mg-ATP complex as its substrate. When little magnesium is present, this step runs more slowly. Source 1, 5↑ supplies Hexokinase uses Mg-ATP, not free ATP: magnesium holds the phosphate groups so that the outermost one can be transferred to glucose. Glucose-6-phosphate is then ready for further breakdown. established physiology Source 4, 1
   ⚖ When the balance tips

   too much — More magnesium does not speed up this step without limit: once the ATP is loaded with magnesium, glucose and hexokinase itself set the limit.

   too little — If little magnesium is present, less Mg-ATP is available to hexokinase, and glucose is converted to glucose-6-phosphate more slowly.

   established physiology · Source 1, 5

8. Glucose-6-phosphate → Glycolysis Glucose-6-phosphate is the entry point to glycolysis, the breakdown of sugar to release energy. Magnesium is needed for this pathway. Several of its enzymes use ATP as Mg-ATP. Source 5↑ supplies Several enzymes of glycolysis use ATP in the form of Mg-ATP or form it anew. In the end, the cell gains more ATP from one sugar molecule than it put in. established physiology Source 5, 4
   ⚖ When the balance tips

   too much — If plenty of magnesium is present, the magnesium-dependent steps are supplied; the pace is then set by the glucose supply and the enzymes themselves.

   too little — If little magnesium is present, the magnesium-dependent steps run more slowly, and the cell gains ATP from sugar less quickly.

   established physiology · Source 5, 4

9. Magnesium in the cell → NMDA receptor The NMDA receptor is a calcium channel opened by the messenger glutamate. Magnesium sits in its pore and has to leave before calcium can flow in. When little magnesium is present, the channel opens more easily. Source 5, 4↓ depletes Magnesium occupies the pore depending on the voltage: at the resting cell it sits tight, and only a prior excitation of the membrane releases it. The channel thus opens only when glutamate and excitation coincide. established physiology Source 5, 4
   ⚖ When the balance tips

   too much — If more magnesium is present, it stays in the pore longer; the channel opens less often, and the excitability of the nerve cell is damped.

   too little — If little magnesium is present, the NMDA receptor is less damped and opens even with weaker excitation; glutamate then acts more strongly.

   established physiology · Source 5, 4

10. NMDA receptor → Calcium influx · Glutamate When the magnesium block is released, calcium flows into the nerve cell and the signal is passed on. At this site magnesium therefore acts like a brake. More magnesium thus damps the excitability of the nerve cell. Source 5↕ both, depending on amount Calcium carries the signal into the nerve cell and switches on enzymes there. In small amounts it serves signal transmission; if it flows in for too long, it burdens the cell, as cell culture and animal models show. observed in studies Source 5
    ⚖ When the balance tips

    too much — If a lot of calcium flows in, the cell has to pump it out or store it; in cell culture and animal models, a sustained overload burdens the mitochondria of the nerve cell.

    too little — If little calcium flows in, for example because magnesium keeps the pore occupied, the signal is passed on more weakly.

    observed in studies · Source 5

Further stations

• Magnesium in food — mineral Magnesium enters the body with food and drink. There it exists only as a dissolved ion with a double positive charge (Mg²⁺). How much of it is absorbed depends on how well it is dissolved. Source 1, 3↑ supplies Food is the only intake of magnesium. How much of it arrives depends on its solubility: only dissolved Mg²⁺ can pass the gut wall. established physiology Source 3, 1
  ⚖ When the balance tips

  too much — If a lot of magnesium arrives at once, the gut absorbs a smaller share of it; what stays in the gut draws water osmotically into the gut lumen.

  too little — If little magnesium arrives, the gut absorbs a larger share of it and the kidneys recover more; the bones serve as a reserve.

  established physiology · Source 3, 1

• Magnesium in the cell — mostly bound Inside the cell, magnesium is the second most common positively charged ion after potassium. It is mostly bound: to proteins, to ATP and to other negatively charged molecules. When little is present, calcium enters nerve and muscle cells more easily. Source 4, 1↕ both, depending on amount Bound magnesium stabilises ATP, proteins and genetic material; a small free fraction acts as a regulator of enzymes and ion channels. The cell keeps this free fraction within narrow limits via channels and transporters. established physiology Source 4, 1
  ⚖ When the balance tips

  too much — If more magnesium flows into the cell, binding sites bind it and transporters release it again; the free fraction rises only slightly.

  too little — If there is little magnesium in the cell, channels for calcium and potassium are less restrained; calcium enters nerve and muscle cells more easily, and they are excited more easily.

  established physiology · Source 4, 1

• Glucose — blood sugar In the cell, glucose first receives a phosphate group before it is broken down further. The phosphate group comes from Mg-ATP. Source 5

Cofactors in this pathway

• ATP — Forms the Mg-ATP complex with magnesium, the form used by enzymes such as hexokinase, i.e. kinases and ATPases Source 4, 1
• Sodium — The transporter CNNM4 probably releases magnesium into the blood in the colon in exchange for sodium as the exit step Source 1In the ORY catalogue as a laboratory value: Natrium (intrazellulär)
• Potassium — Its recycling in the loop of Henle builds the voltage that drives magnesium back between the cells into the blood Source 2In the ORY catalogue as a laboratory value: Kalium (intrazellulär)
• Calcium — Flows in through the NMDA receptor once magnesium has left the pore; with little Mg, this happens more easily Source 5In the ORY catalogue as a laboratory value: Calcium (intrazellulär)
• Glutamate — Messenger that opens the NMDA receptor, in whose pore magnesium sits; magnesium damps its effect Source 5In the ORY catalogue as a laboratory value: Glutamat

What acts on this pathway

• Acid blockers — Proton pump inhibitors raise the pH in the gut. It has been described that magnesium then stays less well dissolved and the channel TRPM6 in the large intestine is less active. Source 1
• Diuretics — Loop diuretics inhibit the transporter NKCC2 in the loop of Henle; this removes the electrical gradient that drives magnesium back between the cells. Lower magnesium levels have also been described with thiazide diuretics. Source 1

Sources

1. Kröse JL, de Baaij JHF. Magnesium biology. Nephrol Dial Transplant 2024 · PubMed 38871680
2. de Baaij JHF. Magnesium reabsorption in the kidney. Am J Physiol Renal Physiol 2023 · PubMed 36633869
3. Schuchardt JP, Hahn A. Intestinal Absorption and Factors Influencing Bioavailability of Magnesium — An Update. Curr Nutr Food Sci 2017 · PubMed 29123461
4. de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev 2015 · PubMed 25540137
5. Kirkland AE, Sarlo GL, Holton KF. The Role of Magnesium in Neurological Disorders. Nutrients 2018 · PubMed 29882776

Related pathways

• GABA, glutamate and glutamine — Natrium (intrazellulär), Kalium (intrazellulär)
• Gut fermentation and breath gases — Natrium (intrazellulär), Calcium (intrazellulär)
• Gluten antibodies — Calcium (intrazellulär), Glutamat
• HbA1c and insulin — Kalium (intrazellulär), Calcium (intrazellulär)
• Pancreatic elastase — Natrium (intrazellulär), Calcium (intrazellulär)

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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