Magnesium is one of the body’s true workhorses, acting as a cofactor in more than 300 enzymatic reactions — including the ones that produce cellular energy and keep nerves and muscles firing correctly. Despite its importance, intake is often marginal: modern diets skew away from the nuts, seeds, legumes, whole grains and leafy greens that supply it, and both intake and absorption tend to decline with age. Frank deficiency is uncommon in healthy people, but mild shortfalls are widespread — and, because the symptoms are vague (fatigue, muscle cramps, poor sleep), they are easy to overlook [1].
Blood pressure and the heart
The clearest benefit of supplementing is on blood pressure. A meta-analysis of randomized, placebo-controlled trials found that magnesium (a median of ~370 mg/day for three months) lowered systolic pressure by about 2 mmHg and diastolic by about 1.8 mmHg [2]. A more recent umbrella review — pooling multiple meta-analyses — confirmed the effect and sharpened the dosing: reductions were most reliable at doses of 400 mg/day or more taken for at least 12 weeks [3]. These are modest changes on their own, but at a population level even small shifts in blood pressure meaningfully affect heart-disease and stroke risk.
Blood sugar and metabolism
Magnesium is closely tied to how the body handles glucose, and low levels are consistently linked to a higher risk of type 2 diabetes. In people who already have type 2 diabetes, a 2025 meta-analysis of 23 trials found that supplementation raised magnesium levels and lowered fasting blood glucose, with the clearest effects in older participants and longer courses [4]. This metabolic role is part of why chronically low magnesium shows up so often alongside cardiovascular and metabolic disease [1].
Sleep and stress
Magnesium’s reputation as a calming, sleep-promoting mineral is popular — and here honesty is important, because the science is thinner than the marketing. A systematic review of older adults with insomnia found that magnesium helped people fall asleep about 17 minutes faster than placebo, but the underlying trials were few, small and of low quality [5]. Similarly, a review of magnesium for anxiety and stress found suggestive benefits in people already prone to anxiety, again limited by weak study quality [6]. The reasonable reading: given how cheap, safe and well-tolerated magnesium is, it’s a low-risk thing to try for sleep or stress — but treat it as a gentle aid, not a reliable sedative.
How much, and which form
Adults need roughly 310–420 mg/day, and food is the best source [1]. If supplementing, the form matters: magnesium citrate and glycinate are well absorbed, whereas cheap magnesium oxide is poorly absorbed and more likely to cause the main side effect — loose stools. High doses act as a laxative, which is the body’s natural ceiling on overdoing it. One genuine caution: people with significant kidney disease should not supplement without medical advice, since impaired kidneys can’t clear excess magnesium.