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Category Health & Nutrition

Serum Correction

Measured Serum Mg (mg/dL) Normal range: 1.7–2.2

Serum Albumin (g/dL) Normal range: 3.5–5.5

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Age (years)

Biological Sex

Special Status

Daily Intake

Estimated Dietary Mg (mg/day) Avg. US adult: ~250 mg/day

Supplement Dose (mg elemental)

Supplement Form

Medications & Conditions

Proton Pump Inhibitor (PPI) Loop Diuretic Type 2 Diabetes Chronic Kidney Disease High Alcohol Intake GI Disorder (Crohn's, Celiac)

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About

Serum magnesium tests report total magnesium, but roughly 0.8% of body stores reside in blood. A "normal" serum value of 1.7 - 2.2 mg/dL can mask chronic intracellular depletion. Corrected magnesium accounts for albumin binding: approximately 33% of serum Mg is protein-bound, so hypoalbuminemia artificially lowers measured values. This calculator applies the albumin-correction formula to your serum magnesium and cross-references your total daily intake (diet + supplements) against the Institute of Medicine RDA for your demographic bracket. It flags supplement forms with poor bioavailability (magnesium oxide absorbs at roughly 4% versus 25 - 30% for citrate or glycinate) and warns when medications such as proton pump inhibitors or loop diuretics accelerate renal magnesium wasting.

Getting this wrong matters. Subclinical magnesium deficiency correlates with increased risk of type 2 diabetes, cardiovascular events, and osteoporosis. Overcorrection beyond the 350 mg/day supplemental UL set by the IOM can cause osmotic diarrhea and, in renal impairment, dangerous hypermagnesemia. This tool approximates absorption assuming normal gastrointestinal function. Pro tip: if you take a PPI, your effective absorption drops further and you should discuss ionized magnesium testing with your physician.

Formulas

The albumin-corrected serum magnesium formula compensates for the protein-bound fraction. Because approximately 33% of serum magnesium binds to albumin, measured values underestimate true ionized magnesium when albumin is low.

Mg_corrected = Mg_measured + 0.005 × (4.0 − Alb_measured)

Where Mg_corrected = corrected serum magnesium in mg/dL, Mg_measured = lab-reported serum magnesium in mg/dL, Alb_measured = serum albumin in g/dL, and 4.0 g/dL is the assumed normal albumin reference.

The daily intake gap is computed as:

Gap = RDA − (D_intake + S_dose)

Where D_intake = estimated dietary magnesium intake in mg/day, and S_dose = elemental magnesium from supplements in mg/day. A positive Gap indicates a shortfall relative to the RDA. The absorbed amounts are estimated as:

Mg_absorbed = D_intake × 0.35 + S_dose × B_form

Where B_form is the bioavailability fraction specific to the supplement form (e.g., 0.27 for citrate, 0.04 for oxide).

Reference Data

Age Group	Sex	RDA mg/day	Pregnancy mg/day	Lactation mg/day	UL (Suppl.) mg/day
0 - 6 mo	Both	30 (AI)	-	-	ND
7 - 12 mo	Both	75 (AI)	-	-	ND
1 - 3 yr	Both	80	-	-	65
4 - 8 yr	Both	130	-	-	110
9 - 13 yr	Both	240	-	-	350
14 - 18 yr	Male	410	-	-	350
14 - 18 yr	Female	360	400	360	350
19 - 30 yr	Male	400	-	-	350
19 - 30 yr	Female	310	350	310	350
31 - 50 yr	Male	420	-	-	350
31 - 50 yr	Female	320	360	320	350
51 - 70 yr	Male	420	-	-	350
51 - 70 yr	Female	320	-	-	350
71+ yr	Male	420	-	-	350
71+ yr	Female	320	-	-	350
Supplement Form Bioavailability
Magnesium Citrate		Absorption: ~25 - 30%		Good solubility
Magnesium Glycinate		Absorption: ~24%		Low GI side effects
Magnesium Oxide		Absorption: ~4%		High elemental Mg, poor uptake
Magnesium Chloride		Absorption: ~20%		Moderate
Magnesium Taurate		Absorption: ~15 - 20%		Cardiovascular research interest
Magnesium L-Threonate		Absorption: ~15%		CNS penetration research
Magnesium Malate		Absorption: ~20 - 25%		Krebs cycle substrate
Magnesium Sulfate		Absorption: ~4 - 7% (oral)		Primarily IV/IM use

Frequently Asked Questions

Approximately 33% of circulating magnesium is bound to albumin. When albumin drops below the reference of 4.0 g/dL (common in hospitalized, elderly, or malnourished patients), the total serum magnesium reading appears lower than the physiologically active ionized fraction. The correction formula adds 0.005 mg/dL of Mg for every 1.0 g/dL albumin is below 4.0. Without correction, clinicians may over-diagnose hypomagnesemia or miss a true deficiency masked by high albumin.

Magnesium oxide contains roughly 60% elemental magnesium by weight, the highest of any oral form, but its fractional absorption is approximately 4%. A 500 mg magnesium oxide tablet delivers about 300 mg elemental Mg, of which only ~12 mg is absorbed. Magnesium citrate at 16% elemental Mg with ~27% absorption from a 500 mg tablet delivers ~21.6 mg absorbed. Glycinate at ~14% elemental with ~24% absorption yields ~16.8 mg from the same tablet weight. Oxide is therefore the least efficient despite appearing strongest on the label.

The reference range for serum magnesium is 1.7-2.2 mg/dL. A corrected value below 1.7 mg/dL indicates hypomagnesemia. Values below 1.2 mg/dL are considered severe and can cause cardiac arrhythmias, tetany, and seizures. However, even values within the "normal" range (1.7-1.8 mg/dL) may reflect subclinical depletion because only 0.8% of total body magnesium resides in blood. Intracellular or RBC magnesium testing provides better assessment of true stores.

Yes. The FDA issued a safety warning in 2011. PPIs reduce active magnesium transport in the intestine via TRPM6 channels. Clinically significant hypomagnesemia typically develops after prolonged use exceeding 12 months, though cases have been reported at 3 months. PPI-induced hypomagnesemia is resistant to oral supplementation because the absorption mechanism itself is impaired. Patients on long-term PPIs should have serum magnesium checked at baseline and periodically, with consideration for IV repletion if oral supplements fail to normalize levels.

The IOM set 350 mg/day as the UL specifically for supplemental magnesium (not dietary). This threshold is based on osmotic diarrhea as the critical adverse effect, which occurs in most individuals above this dose. The UL does not apply to food sources because dietary magnesium has never been shown to cause adverse effects at any intake level. In renal impairment (GFR below 30 mL/min), even doses below the UL can cause dangerous hypermagnesemia (above 4.9 mg/dL) leading to hypotension, respiratory depression, and cardiac arrest.

The 35% figure is the midpoint of the established range of 30-40% fractional absorption for dietary magnesium from a mixed diet, as reported in balance studies compiled by the IOM. Absorption varies with magnesium status (depleted individuals absorb up to 80%), fiber content (phytates reduce absorption), and concurrent nutrients (high-dose zinc above 142 mg/day competes for absorption). The calculator uses 35% as a population-level estimate. Individual absorption may differ substantially.

No. Sweat magnesium concentration ranges from 0.2-1.5 mmol/L depending on acclimation and exercise intensity. A 2-hour endurance session losing 2 liters of sweat could deplete 5-36 mg of additional magnesium. This loss is modest relative to RDA values of 310-420 mg/day but becomes significant with chronic high-volume training. Athletes should add 10-20% to their RDA target. This tool does not adjust for exercise level and assumes sedentary to moderate activity.