Magnesium

mineralmagnesium atom

What is it

Magnesium is an essential mineral involved in more than 300 enzymatic reactions, including energy production, protein synthesis, muscle and nerve function, blood pressure regulation, and bone health. It is one of the most common nutrient deficiencies in modern diets.

How it works

Magnesium acts as a cofactor for ATP — the body's energy currency must be bound to magnesium to be biologically active. It regulates muscle contraction by competing with calcium, supports nerve signaling, and is needed for DNA and protein synthesis. About 60 percent of body magnesium is in bone; most of the rest is in soft tissue, with less than 1 percent in blood. Magnesium is absorbed mainly in the small intestine through both passive diffusion and active transport. Absorption efficiency drops as dose increases — a 500 mg dose absorbs less efficiently than 100 mg doses spread through the day. The kidneys regulate body magnesium by adjusting excretion.

Evidence for 7 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Correction of magnesium deficiency

Grade A

Strong evidence

Supplementation reliably reverses deficiency, which can cause muscle cramps, weakness, irritability, abnormal heart rhythms, and seizures in severe cases.

Constipation

Grade A

Strong evidence

Magnesium citrate, hydroxide (milk of magnesia), and oxide are effective osmotic laxatives at appropriate doses. This is one of the most reliable supplement uses.

Blood pressure reduction

Grade B

Good evidence

Meta-analyses show small but consistent reductions in blood pressure (around 2-3 mmHg systolic) with supplementation, particularly in people with hypertension or low baseline magnesium.

Migraine prevention

Grade B

Good evidence

400 to 600 mg per day reduces migraine frequency in some trials. The American Academy of Neurology rates magnesium as 'probably effective' for migraine prevention.

Type 2 diabetes risk reduction

Grade B

Good evidence

Observational and supplementation studies suggest improved insulin sensitivity, particularly in people who are deficient.

Sleep quality

Grade C

Moderate evidence

Some trials in older adults with insomnia show modest sleep improvement, but evidence is limited and most trials are small.

Muscle cramps

Grade C

Moderate evidence

Mixed evidence. Useful for cramps related to deficiency, less clear for general or exercise-induced cramps in well-nourished people.

6 commercial forms

Magnesium glycinate (bisglycinate)

highly bioavailable, gentle on stomach

Bound to glycine for good absorption with minimal laxative effect. Often preferred for sleep, anxiety, and people sensitive to other forms.

Magnesium citrate

good absorption, mild laxative

Well absorbed and inexpensive. Has a mild osmotic laxative effect, useful for constipation but unwelcome at higher doses.

Magnesium oxide

poor absorption (around 4 percent), strong laxative

Inexpensive and high in elemental magnesium per mg, but poorly absorbed. Mainly useful as a laxative, not for raising body magnesium status.

Magnesium malate

well absorbed, often used for fatigue

Magnesium bound to malic acid. Popular for fibromyalgia and chronic fatigue, though evidence for advantage over other forms is limited.

Magnesium L-threonate

claimed to cross blood-brain barrier

Marketed for cognitive benefits based on animal studies showing brain magnesium increases. Human evidence is limited and the form is expensive.

Magnesium chloride / sulfate (Epsom salts)

rapidly absorbed orally

Chloride is well absorbed; sulfate is mostly used as oral or transdermal Epsom salt. Topical absorption claims are largely unsupported.

Dosage

The RDA is 400-420 mg per day for adult men and 310-320 mg for women. Most adults fall short of this from food alone. Common supplemental doses are 100 to 400 mg of elemental magnesium. The tolerable upper limit from supplements (not food) is 350 mg per day for adults — exceeding it causes diarrhea but rarely serious harm in people with normal kidney function.

When and how to take it

Magnesium is often recommended in the evening because it has a calming effect on muscles and nerves, and many people find it helps with sleep and restless legs. That said, time of day is flexible — what matters more is consistency. Splitting larger doses (over 300 mg) into two smaller doses through the day improves absorption and reduces digestive side effects. Magnesium absorbs better when taken with food, particularly for forms like magnesium oxide that can otherwise cause stomach upset. Glycinate and citrate are gentler on the stomach.

Food sources

Food	Amount	%DV
Pumpkin seeds, 1 oz	168 mg	40%
Chia seeds, 1 oz	111 mg	26%
Almonds, 1 oz	80 mg	19%
Spinach (boiled), 1/2 cup	78 mg	19%
Cashews, 1 oz	74 mg	18%
Black beans (cooked), 1/2 cup	60 mg	14%
Edamame (cooked), 1/2 cup	50 mg	12%
Dark chocolate (70-85%), 1 oz	65 mg	15%
Avocado, 1 cup	44 mg	10%
Salmon, 3 oz cooked	26 mg	6%

Safety

Magnesium from food is safe at any intake level — kidneys excrete excess. Supplemental magnesium most commonly causes diarrhea and digestive upset, especially in forms like magnesium oxide and magnesium citrate. Very high doses (above 5,000 mg) can cause magnesium toxicity with weakness, low blood pressure, and irregular heartbeat, but this almost never happens in people with normal kidney function. People with kidney disease can develop dangerous hypermagnesemia even at modest doses and should not take magnesium supplements without medical supervision.

Who should be cautious

People with chronic kidney disease should not take magnesium without medical guidance. Pregnant and breastfeeding women have slightly higher needs (350 mg and 310 mg respectively). People with myasthenia gravis should avoid IV magnesium and discuss oral supplements with their doctor.

Interactions

Magnesium reduces absorption of bisphosphonates (osteoporosis drugs), tetracycline and quinolone antibiotics, and some thyroid medications — separate them by at least 2 hours. Loop diuretics and thiazides can increase magnesium loss in urine. Proton pump inhibitors used long-term can cause magnesium deficiency.

Frequently asked questions

Which form of magnesium is best?⌄

It depends on the goal. Glycinate for general use, sleep, and anxiety (gentle on the stomach). Citrate for constipation. Oxide is cheap but poorly absorbed. Malate is popular for fatigue. L-threonate for cognitive aims, though evidence is limited.

Should I take magnesium at night?⌄

Many people do because of its calming effect on muscles and nerves. Time of day is flexible, but evening dosing is reasonable, especially for sleep support.

How much magnesium causes diarrhea?⌄

It depends on the form and individual sensitivity. Most people tolerate 300 to 400 mg of glycinate or malate. Citrate and oxide cause diarrhea more easily, sometimes at lower doses.

Can magnesium help me sleep?⌄

Possibly. Some trials show modest improvement in sleep quality, especially in older adults or people with low magnesium status. The effect is not dramatic.

Does magnesium help anxiety?⌄

Some trials suggest modest benefit, particularly with magnesium glycinate. Effects are gentler than prescription anti-anxiety medications.

References

NIH ODS Magnesium Fact Sheet — NIH Office of Dietary Supplements link

Track Magnesium with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.