Find out how much magnesium you need per day and whether you're likely getting enough from your diet.
Magnesium is involved in over 300 enzyme reactions in the body. Key roles include:
Muscle and nerve function: Magnesium regulates muscle contraction and nerve signals. Low magnesium causes cramps, twitches, and restless legs.
Blood sugar control: Magnesium helps insulin move glucose into cells. Low magnesium is associated with insulin resistance and higher risk of type 2 diabetes.
Blood pressure regulation: Adequate magnesium helps relax blood vessels and maintain healthy blood pressure.
Bone health: About 60% of your body's magnesium is stored in bone. It works alongside calcium and vitamin D for bone density.
Sleep and mood: Magnesium helps regulate melatonin and GABA (a calming neurotransmitter). Many people report better sleep with adequate magnesium intake.
Heart rhythm: Magnesium is critical for a normal heartbeat. Severe deficiency can cause dangerous arrhythmias.
The upper limit for supplemental magnesium is 350mg/day for adults. This does not apply to magnesium from food — only from supplements and medications (like antacids). Excess supplemental magnesium can cause diarrhoea, nausea, and abdominal cramping.
Common forms:
Magnesium citrate: Well absorbed. Can have a mild laxative effect. Good general-purpose choice.
Magnesium glycinate: Well absorbed, less likely to cause GI side effects. Often recommended for sleep and anxiety.
Magnesium oxide: Cheap but poorly absorbed (only ~4%). Often used in antacids. Not the best choice for correcting deficiency.
Magnesium threonate: Crosses the blood-brain barrier. Marketed for cognitive function. More expensive, limited evidence.
Important: Magnesium supplements can interact with some antibiotics, bisphosphonates (osteoporosis medications), and diuretics. Take supplements at least 2 hours apart from these medications. Talk to your GP or pharmacist before starting a supplement if you take regular medications or have kidney disease.
See your GP about magnesium if you have:
Persistent muscle cramps or twitches (especially at night). Heart palpitations or irregular heartbeat. Chronic fatigue that doesn't improve with rest. Numbness or tingling. Difficult-to-control blood sugar (if diabetic). Chronic diarrhoea or GI conditions that may affect absorption. Been on proton pump inhibitors (PPIs) for more than a year.
Your GP can check magnesium with a blood test, although serum magnesium may appear normal even when body stores are low (only 1% of magnesium is in the blood). If your GP suspects deficiency based on symptoms and risk factors, a trial of supplementation may be recommended.