Magnesium Blog Series: The Forgotten Nutrient | Part 2 – How the Body Handles Mg

August 6, 2018 • 2 min read
Summary

Magnesium is regulated through gut absorption, renal filtration, reabsorption, and excretion, and exchange with the reservoir of magnesium in bone.

The average human body contains about 24 g of magnesium.11 Most magnesium in the body is intracellular, with >90% located in bone, muscle, and other soft tissues; serum levels represent only ~1% of total body magnesium stores.10,11 In humans, magnesium is regulated through three key mechanisms: absorption by the gut; renal filtration, reabsorption, and excretion; and exchange with the reservoir of magnesium in bone.10,12 About 25%-75% of magnesium consumed in the diet is absorbed by the gut; the degree of absorption depends on multiple factors, most notably magnesium status.11

The kidneys filter about 2.4 g of magnesium per day, reabsorbing ~95% and excreting any excess in the urine.11 When magnesium levels are low, the kidneys increase reabsorption and urinary concentrations fall; when magnesium intake exceeds requirements, the excess magnesium is excreted in the urine. Because magnesium is tightly regulated by the kidneys, urinary magnesium levels are a fairly good indicator of magnesium intake; levels <80 mg/d suggest risk for magnesium deficiency.13

Factors that may contribute to magnesium deficiency include inadequate dietary intake, reduced absorption by the gut, increased losses through the gut or kidney, excessive sweating (e.g., vigorous exercise), increased magnesium needs (e.g., pregnancy, chronic stress), and the effects of certain medications (Figure 2).[4,14]

Figure 2. Factors that may contribute to magnesium (Mg) deficiency. GI: gastrointestinal

When dietary intake and renal reabsorption of magnesium are insufficient to meet physiological needs, magnesium may be mobilized from muscle and bone, potentially contributing to hidden deficits of magnesium.11,12 These hidden or subclinical magnesium deficiencies are especially concerning, as they appear to be common, are difficult to diagnose, and may contribute to a wide range of chronic health problems.15,16 Several sources indicate that up to one-third of the general population has a subclinical magnesium deficit.9,17 However, the prevalence of subclinical magnesium deficiency may be higher than estimated, as current methods for determining body magnesium levels (e.g., serum, urine, dietary intake) are likely inaccurate.18

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9. Costello RB, Elin RJ, Rosanoff A, et al. Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium: The Time Has Come. Adv Nutr. Nov 2016;7(6):977-993.

10. Vormann J. Magnesium: nutrition and metabolism. Mol Aspects Med. Feb-Jun 2003;24(1-3):27-37.

11. Jahnen-Dechent W, Ketteler M. Magnesium basics. Clin Kidney J. Feb 2012;5(Suppl 1):i3-i14.

12. Rude RK, Gruber HE. Magnesium deficiency and osteoporosis: animal and human observations. J Nutr Biochem. Dec 2004;15(12):710-716.

13. Nielsen FH, Milne DB, Gallagher S, Johnson L, Hoverson B. Moderate magnesium deprivation results in calcium retention and altered potassium and phosphorus excretion by postmenopausal women. Magnes Res. Mar 2007;20(1):19-31.

14. Schwalfenberg GK, Genuis SJ. The Importance of Magnesium in Clinical Healthcare. Scientifica (Cairo). 2017;2017:4179326.

15. Hermes Sales C, Azevedo Nascimento D, Queiroz Medeiros AC, Costa Lima K, Campos Pedrosa LF, Colli C. There is chronic latent magnesium deficiency in apparently healthy university students. Nutr Hosp. Jul 1 2014;30(1):200-204.

16. Elin RJ. Re-evaluation of the concept of chronic, latent, magnesium deficiency. Magnes Res. Dec 2011;24(4):225-227.

17. Mejia-Rodriguez F, Shamah-Levy T, Villalpando S, Garcia-Guerra A, Mendez-Gomez Humaran I. Iron, zinc, copper and magnesium deficiencies in Mexican adults from the National Health and Nutrition Survey 2006. Salud Publica Mex. May-Jun 2013;55(3):275-284.

18. 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(1):e000668.

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