Magnesium: The Most Underused Mineral on the Shelf

Why magnesium matters

Magnesium is involved in more than 300 enzymatic reactions in the body, including energy production, muscle and nerve function, blood sugar regulation, blood pressure regulation, and bone health. Adequate magnesium status supports several physiological systems that most adults do not think about until something is off.

Who is likely to benefit

• Patients with documented magnesium deficiency, which can develop from dietary inadequacy, GI losses, or kidney losses.
• Patients on long term proton pump inhibitors, which reduce magnesium absorption.
• Patients on certain diuretics including loop diuretics (furosemide).
• Patients with diabetes, who have higher magnesium losses.
• Patients with alcohol use disorder.
• Patients with chronic GI conditions affecting absorption.
• Older adults with lower dietary intake.
• Patients with frequent muscle cramps, particularly nocturnal leg cramps.
• Patients with migraine. Magnesium has modest preventive evidence.
• Patients with constipation, depending on the form chosen.

The forms and what they do best

Magnesium oxide

Inexpensive, widely available, but poorly absorbed. Useful primarily as a laxative or for short term constipation relief. Not the best choice for correcting deficiency.

Magnesium citrate

Reasonable absorption. Mild laxative effect at higher doses. Useful for patients who also have constipation. Common, affordable, and a reasonable general purpose choice.

Magnesium glycinate

Well absorbed. Gentle on the gut. Good choice for patients who need supplementation but want to avoid the laxative effect. Often used for sleep, muscle cramps, and general supplementation.

Magnesium malate

Well absorbed. Sometimes used for muscle pain and fatigue. Reasonable choice for daytime use.

Magnesium L threonate

Marketed for cognitive benefit based on animal studies showing brain penetration. Limited human evidence. Expensive. Not the first form I reach for.

Magnesium chloride

Topical forms are popular but absorption through skin is limited. Oral forms are reasonable but less common than citrate or glycinate.

Dosing

The recommended dietary allowance for adults is 310 to 420 mg daily depending on age and sex. Supplemental doses for specific purposes typically range from 200 to 400 mg daily, with the upper limit from supplements set at 350 mg per day (food sources are not subject to this limit).

Higher doses (500 to 600 mg daily) are sometimes used for migraine prevention under clinical guidance. Start lower and titrate up to reduce GI side effects.

Side effects and safety

Diarrhea and loose stools are the most common side effects, particularly with magnesium oxide and citrate. Splitting the dose between morning and evening, or using glycinate, often resolves this.

Patients with kidney disease should be careful with magnesium supplementation. The kidney removes excess magnesium, and impaired kidney function can lead to magnesium accumulation. Always check with your pharmacist before starting magnesium if you have CKD.

Drug interactions to know

• Magnesium reduces absorption of several antibiotics including tetracyclines and fluoroquinolones. Separate by 4 hours.
• Magnesium reduces absorption of bisphosphonates (osteoporosis medications). Take bisphosphonate first thing in the morning, magnesium later in the day.
• Magnesium can reduce absorption of thyroid medication. Separate by at least 4 hours.
• Patients on multiple diuretics may have variable effects on magnesium.

Food sources

Nuts (almonds, cashews, pumpkin seeds), legumes, leafy greens, whole grains, and dark chocolate are good dietary sources. Many adults do not consume enough through diet alone.

When to talk to a pharmacist

• You have kidney disease.
• You take antibiotics, thyroid medication, or bisphosphonates.
• You are on long term proton pump inhibitors.
• You are considering magnesium for migraine prevention.
• You have frequent muscle cramps.
• You are pregnant or breastfeeding.

This article is for general information only and is not a substitute for personalized medical advice. Before starting or changing any medication, including over the counter products and supplements, talk with your pharmacist or physician about your specific situation.