Written & reviewed by
Dr. Jun Chung
NZ Chiropractic Board registered Chiropractor · Auckland Wellness Centre · NZCC graduate · Sports Nutrition Certified · TPI · ART
Jung Min Lee
Pharmacist · PSNZ APC registration 12439 · NZ-registered · Co-developer, WIIP supplements
Not all magnesium supplements are equal. If you've tried magnesium before and felt nothing — or spent more time in the bathroom than expected — the form you took is probably why. Here's what a NZ pharmacist wants you to know before you buy.
The magnesium form problem
Walk into any NZ pharmacy and you'll see magnesium oxide, magnesium citrate, magnesium glycinate, and magnesium chloride side by side. They contain the same mineral. The difference is bioavailability — how much your body actually absorbs.
| Form | Bioavailability | Common use | Note |
|---|---|---|---|
| Oxide | ~4% | Cheap supplement filler | Mostly laxative effect |
| Citrate | ~25–30% | Constipation, general Mg | Loose stools at higher doses |
| Glycinate | ~80% | Sleep, muscle, anxiety | Gentle on gut |
| Malate | ~60% | Energy, fibromyalgia | More stimulating |
Magnesium glycinate is chelated — the mineral is bound to the amino acid glycine. Glycine itself has calming properties. The combination makes glycinate the preferred form for sleep support and muscle relaxation without GI side effects.
How much magnesium do New Zealanders actually need?
The NZ Ministry of Health recommended dietary intake (RDI) for magnesium is 310–320mg/day for adult women and 400–420mg/day for adult men. Most NZ adults fall short, particularly those who:
- Eat a processed food diet (refining removes up to 80% of Mg from grains)
- Drink alcohol regularly (alcohol increases urinary Mg excretion)
- Exercise intensely (sweat losses add up)
- Take proton pump inhibitors (reduces Mg absorption)
What "elemental magnesium" means on a label
This is where most shoppers get confused. A capsule might say "400mg Magnesium Glycinate" — but the elemental magnesium in that is closer to 50mg. The glycinate complex is heavier than the mineral itself.
Look for the elemental magnesium figure — usually in smaller print below the compound dose. Effective sleep and muscle support doses in research range from 200–400mg elemental per day.
When to take magnesium for sleep
Taken 30–60 minutes before bed, magnesium glycinate supports the transition to sleep by activating GABA receptors — the same receptors targeted by sleep medications, but through a gentler, physiological mechanism. Glycine independently lowers core body temperature, which is part of the sleep onset process.
Magnesium and muscle cramps
The relationship between magnesium and muscle cramps is often overstated in marketing but real in specific contexts. Cramps from exercise, pregnancy, or certain medications (diuretics) respond better to magnesium than idiopathic nocturnal cramps. If cramps persist, see a GP — they can indicate other causes.
Reviewed by Dr. Jun Chung (NZ Chiropractic Board registered Chiropractor) and Jung Min Lee (Pharmacist, PSNZ APC 12439). Dietary supplements are not medicines and are not intended to diagnose, treat, cure, or prevent any disease. If you have a health concern, consult your GP or a registered health professional.