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

Key Topics: Lifestyle Health & Wellness

August 6, 2018 • 2 min read

Magnesium

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Summary

Magnesium is regulated in the body by 3 mechanisms: absorption by the gut; renal filtration, reabsorption, and excretion; and exchange with the magnesium reservoir in bone.

The average human body contains about 24 grams of magnesium.₁₁ Most magnesium in the body is intracellular, with greater than 90 percent located in bone, muscle, and other soft tissues; serum levels represent only about one percent 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._10,11 About 25 percent to 75 percent 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 grams of magnesium per day, reabsorbing about 95 percent 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 less than 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 depicting factors that contribute to magnesium deficiency.

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 deficiency._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

Read Part 3 of the Magnesium Blog Series: The Forgotten Nutrient.

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References

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