Magnesium and menopause: what it is actually for

Why it is plausible

Magnesium is a cofactor in several hundred enzyme reactions. It is directly involved in muscle relaxation, opposing calcium's contracting effect, in nerve signalling including at the NMDA receptor, in the activity of vitamin D, and in bone structure, where around half the body's magnesium is stored.

Dietary intake below recommended levels is common in Western populations, particularly with low intakes of leafy greens, nuts, legumes and whole grains.

That combination — a plausible mechanism and a plausible shortfall — is why it is recommended so widely. Plausibility is not the same as demonstrated benefit, and the two get conflated here as much as anywhere.

What the evidence supports

Reasonable: muscle cramps, where magnesium is used with some support, and constipation, where certain forms act as an osmotic laxative reliably. Correcting a documented deficiency obviously helps the symptoms that deficiency causes.

Limited: sleep. Some small trials in older adults suggest modest improvement in sleep quality, but the evidence base is not strong and studies specifically in menopausal women are few.

Weak: hot flashes. A small trial in breast cancer survivors generated interest but larger controlled work has not established a benefit.

Unclear but biologically reasonable: bone health, where magnesium is structurally necessary, though supplementation beyond requirements has not been shown to add benefit.

The forms differ, and it matters

This is the most practically useful section, because form determines both absorption and side effects:

• Oxide: cheap, poorly absorbed, strong laxative effect. The form in many inexpensive products
• Citrate: reasonably absorbed, still with a laxative effect at higher intakes
• Glycinate: well absorbed and gentler on the bowel, which is why it is the form usually suggested where sleep or cramps are the target
• Malate, threonate and others: marketed for specific purposes, with limited comparative evidence for those claims

Cautions

Magnesium is cleared by the kidneys, so anyone with reduced kidney function can accumulate it to harmful levels and should not supplement without medical advice.

It interferes with the absorption of several medicines, including some antibiotics, bisphosphonates used for osteoporosis, and thyroid hormone. Separating doses in time is the usual approach, which is a pharmacist conversation.

Diarrhoea is the usual sign of too much, and it resolves on reducing. Serum magnesium testing is a poor measure of body stores, since most magnesium is inside cells and in bone, so a normal result does not exclude a shortfall.

When to see someone

Check with a clinician or pharmacist before supplementing with kidney disease, heart block, or if you take bisphosphonates, thyroid medication or antibiotics.

Persistent cramps, twitching or poor sleep are worth investigating rather than supplementing indefinitely. Iron deficiency, thyroid disease and restless legs syndrome all present this way and are treated differently.