What it is. Magnesium is an essential mineral involved in nerve signaling, muscle relaxation and normal energy metabolism. Because it interacts with NMDA and GABA-related signaling, it is often marketed as a sleep supplement. The biology is plausible, but the clinical evidence is more modest than the marketing.
What the evidence says. Small trials in older adults with insomnia suggest magnesium may improve sleep time, sleep efficiency and early-morning waking. A systematic review found the evidence promising but limited: studies are few, sample sizes are small and methods vary. That means magnesium is not a universal sleep pill, but it can be reasonable when intake is low or muscle tension/restlessness is part of the picture.
WHO is most likely to benefit. People with low dietary magnesium intake are the best candidates. Diets low in nuts, seeds, legumes, whole grains and leafy greens can easily miss the mark. Older adults may also be more vulnerable, especially if appetite is low or medications affect magnesium balance. For someone already eating plenty of magnesium-rich foods, the effect may be small or absent.
Which form to choose. Magnesium glycinate is popular because it is usually gentle on the gut. Citrate is well absorbed but can loosen stools. Oxide is cheap but less attractive for sleep because it is more likely to cause gastrointestinal side effects and is not absorbed as well. Magnesium L-threonate is marketed for the brain, but it is not the default choice for ordinary sleep support.
How to use it. A practical dose is often 100-200 mg elemental magnesium in the evening. More is not automatically better; higher doses increase the risk of diarrhea. People with kidney disease or those taking medications that interact with minerals should check with a clinician first.
Bottom line. Magnesium can help some people sleep better, especially when intake is low, but it is a support tool. Light exposure, caffeine timing, alcohol reduction and a consistent sleep window remain the foundations.