What drains magnesium from your body?

The three exits, and the kidney as the regulated door that most drains open wider

What drains magnesium from your body is a question about exits, and the body has three, of very different sizes. Exit one, the kidney, the regulated door: the kidneys filter magnesium from the blood continuously and reabsorb most of it, in the loop of Henle and the distal tubule, excreting only the surplus, so that a replete person on a steady diet loses in the urine what they took in and a deficient person's kidneys conserve magnesium down to very low urinary losses, the regulation that keeps serum magnesium in its narrow range. Most of the things that drain magnesium work by propping that door open. Alcohol, heavy and sustained, directly increases urinary magnesium excretion and is the commonest cause of clinically low magnesium in otherwise-fed adults, the drain no supplement outruns while the drinking continues. Loop and thiazide diuretics, furosemide and bendroflumethiazide, act on the very segments that reabsorb magnesium and increase its loss as a known effect, a pharmacist's conversation and often a reason a doctor adds magnesium. High blood sugar, in poorly controlled diabetes, drags magnesium out through osmotic diuresis, low magnesium being common in diabetes and improving with glucose control. Certain other drugs, some chemotherapy agents, calcineurin inhibitors and others, waste magnesium through the tubule. And rare inherited tubular disorders leave the door permanently ajar. Caffeine, often named, is a minor diuretic whose effect on magnesium balance at ordinary intakes is a footnote, and a high-sodium diet modestly increases urinary magnesium, another footnote against the main drains.

The gut and sweat exits, the magnitudes side by side, and what a lifter does about each

Exit two, the gut: magnesium can be lost before it is ever absorbed, or drawn back out afterwards, and the gut door opens with diarrhoea of any cause, with magnesium-containing and other laxatives, with malabsorption from coeliac disease, inflammatory bowel disease, short bowel or pancreatic insufficiency, and with fat malabsorption, which binds magnesium in the gut, the deficiency causes page's second mechanism and a gastroenterologist's territory where it is a disease rather than a bout. Exit three, sweat: magnesium leaves in sweat at low concentrations, and a hard session in heat or a long run loses tens of milligrams, more in a very hot environment or a very long effort, the sweat page's arithmetic, a real drain and a small one, replaced by the next meal and never the reason a lifter is deficient on its own. The magnitudes side by side: the kidney is the main drain and the one the serious causes act on, alcohol, diuretics, diabetes and drugs; the gut is a large drain when disease opens it and a passing one in a bout of diarrhoea; and sweat is a small drain that heat and duration enlarge modestly, with caffeine and sodium as footnotes. What a lifter does about each: nothing for sweat beyond eating; a doctor for the gut where disease is the cause and fluids and food for a bout; and, for the kidney door, the drinking reduced, the diuretic and the glucose discussed with the prescriber, with a supplement holding status while the door is addressed and never substituting for closing it, the diet audit deciding whether a training diet was also running light, which it often is. The exits filed: urine as the regulated main drain, opened by alcohol, diuretics, glucose and drugs; the gut, opened by diarrhoea, laxatives and malabsorption; and sweat, small and enlarged by heat, with the worked example being the top-up for a diet the drains outrun, bisglycinate at 300mg elemental, £19.99 for 90 days at 22p.

The verdict, three doors and one that matters most

What drains magnesium from your body: three exits, the kidney as the regulated main drain that alcohol, loop and thiazide diuretics, high blood sugar and certain drugs prop open, the gut as a large drain when diarrhoea, laxatives, malabsorption or bowel disease open it and a passing one in a bout, and sweat as a small drain that heat and long sessions enlarge to tens of milligrams a session, with caffeine and sodium as footnotes, each door addressed at its source and a supplement holding status while it is. The top-up for a diet the drains outrun: Futuro Labs Magnesium Glycinate, bisglycinate, 300mg elemental at 80% NRV, £19.99 for 90 days at 22p a day.

What to check on the label

Questions people also ask

What is the biggest drain on magnesium?

The kidney, propped open: heavy alcohol is the commonest cause of clinically low magnesium in fed adults, with loop and thiazide diuretics, poorly controlled blood sugar and certain drugs increasing urinary loss through the same door.

Does sweating drain magnesium?

A little: sweat carries magnesium at low concentrations, so a hard session in heat or a long run loses tens of milligrams, more in extreme heat or duration, replaced by the next meal and never the reason a lifter is deficient on its own.

Does coffee drain magnesium?

Barely: caffeine is a minor diuretic whose effect on magnesium balance at ordinary intakes is a footnote against alcohol, diuretics and blood sugar.

How does the gut lose magnesium?

Before absorption, when diarrhoea, laxatives or malabsorption from coeliac disease, inflammatory bowel disease, short bowel or fat malabsorption prevent uptake, a large drain when disease opens it and a passing one in a bout.

Can a supplement keep up with a magnesium drain?

It can hold status while the drain is addressed, but no supplement outruns heavy drinking or an unmanaged diuretic or glucose effect, so the door is closed at its source and the supplement tops up a diet that also ran light.

Sources

1. The renal magnesium handling literature: the kidney is the main regulated exit for magnesium, reabsorbing most filtered magnesium in the loop of Henle and distal tubule and excreting the surplus, with loss increased by alcohol, loop and thiazide diuretics, high glucose and certain drugs. PubMed record
2. The hypomagnesaemia literature: clinically low serum magnesium presents with cramps, tremor, weakness and, when severe, arrhythmias and seizures, with alcohol misuse, proton-pump inhibitors, diuretics and gastrointestinal loss the common causes, and serum magnesium an imperfect marker of tissue status. PubMed record
3. Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. American Journal of Clinical Nutrition 2000;72(2 Suppl):585S-593S. PubMed record
4. The magnesium and medicines literature: magnesium supplements reduce absorption of tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine when taken together and are spaced from them, while proton-pump inhibitors and some diuretics lower magnesium status, a reason for medical advice in either direction. PubMed record

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