Few nutrients are marketed as hard for better sleep. The evidence is thinner than the advertising suggests.
Magnesium has become the sleep aid of social media. A spoon of powder in the evening, the marketing promises, and sleep turns deep and calm.
The studies that exist are far more cautious. A systematic review of recent trials rates the evidence for magnesium against sleep problems as low to very low.
That does not make magnesium unimportant. It takes part in hundreds of reactions in the body, in the function of muscles and nerves, energy metabolism, bone building.
A genuine deficiency shows up as muscle cramps, irritability and fatigue. The requirement is about 300 milligrams a day for women and 350 for men.
But such a deficiency is rarer than the market implies. Magnesium is plentiful in nuts, seeds, legumes, whole grains and green vegetables.
Anyone eating a reasonably balanced diet usually meets the need from food. A supplement helps where too little actually arrives, not as a general sedative.
When a deficiency is real
A genuine deficiency tends to affect specific groups. Older people absorb less, and some medicines drive excretion, among them acid blockers and diuretics.
Heavy drinking and poorly controlled diabetes also drain the stores. Anyone in one of these groups has a real reason for a supplement, unlike the healthy adult on a mixed diet.
What it actually does for sleep
Where magnesium does improve sleep, the effect is usually small and touches subjective feeling more than measured sleep architecture.
The studies differ widely in dose, form and participants, and their results contradict one another. Those most likely to benefit have a real shortfall or restless legs, not everyone with the odd bad night.
The forms differ. Magnesium oxide is cheap but poorly absorbed and acts mainly as a laxative.
Organic compounds such as magnesium citrate or magnesium glycinate are better tolerated. Anyone correcting a deficiency does better with a well absorbed supplement than with the cheapest option, but should keep expectations for sleep low.
More is not better here. Magnesium is hard to overdose through food, but easier through supplements: the most common result is diarrhoea, and anyone with reduced kidney function should take higher doses only under medical guidance.
A moderate amount in the evening is harmless for most; several times the recommended dose is not.
Magnesium is an important nutrient with a modest role in sleep. Anyone sleeping badly will find the larger levers elsewhere, in fixed hours, less screen time at night and a cool, dark room.
