Magnesium is involved in hundreds of processes in the body, including muscle and nerve function, blood sugar control and bone health. Many adults don’t get enough from food. That’s made magnesium one of the most popular supplements — and one of the most confusing.
How much you need
The recommended intake for adult women is about 310–320mg per day from all sources. The upper limit for supplemental magnesium is 350mg per day — above that, digestive side effects become common. Magnesium from food doesn’t count toward that limit.
The common forms
Magnesium oxide. Contains a lot of magnesium by weight but is poorly absorbed. Often used as a laxative or antacid. Cheap, and common in multivitamins.
Magnesium citrate. Better absorbed. Has a mild laxative effect at higher doses, which makes it useful for constipation.
Magnesium glycinate (bisglycinate). Magnesium bound to the amino acid glycine. Well absorbed and gentle on the stomach. Popular for sleep and relaxation, though evidence for sleep benefits is limited and mostly comes from studies in people who were low in magnesium.
Magnesium L-threonate. Marketed for brain health because it may raise magnesium levels in the brain in animal studies. Human evidence is early and limited.
Magnesium malate, taurate and others. Each is marketed for specific uses, but strong human evidence distinguishing them is scarce.
What the evidence supports
Magnesium supplements may help with constipation, and magnesium is used medically for certain conditions. Evidence for sleep, anxiety, muscle cramps and migraine is mixed — some studies show benefit, particularly in people with low intake, while others don’t.
Food first
Good sources include pumpkin seeds, almonds, spinach, black beans, edamame, whole grains and dark chocolate.
Safety
People with kidney disease should not take magnesium supplements without medical advice. Magnesium can interact with some antibiotics and osteoporosis drugs (bisphosphonates) — separate the doses by a few hours and check with your pharmacist.