What Magnesium Does in the Body: 300 Enzyme Reactions and Why Most People Don't Get Enough

Most people have heard magnesium is important. Very few know why. It’s not just one reaction or one organ system. Magnesium is a cofactor in over 300 enzymatic reactions across the entire body, and without it, basic cell function breaks down.

What Magnesium Actually Does

Start with energy. Every molecule of ATP in your body exists as a complex with magnesium. ATP alone doesn’t work well. It needs to bind Mg2+ to become biologically active (de Baaij et al., 2015, Physiol Rev). That means every time a cell uses energy, from a muscle contraction to a neuron firing, magnesium is required. There’s no workaround.

DNA replication requires magnesium. RNA polymerase needs it. Protein synthesis depends on it. The enzymes that repair DNA damage use it as a cofactor. If you wanted to build a list of the body’s most indispensable mineral, magnesium would be near the top.

Beyond energy and genetics, magnesium controls how calcium moves in and out of muscle cells. This is why the first signs of deficiency are often muscular. When magnesium is low, calcium can’t be properly regulated at the muscle cell membrane, leading to involuntary contractions, cramps, and twitching. The same mechanism applies to cardiac muscle. Severe magnesium deficiency can cause arrhythmias.

The nervous system also depends on magnesium. It blocks NMDA receptors at normal concentrations, acting as a natural brake on excitatory nerve signaling. When magnesium is low, this brake loosens, which may explain why low magnesium correlates with higher rates of anxiety and hyperexcitability in some studies. The research here is correlational, not definitive, but the mechanism is real.

Why Most People Don’t Get Enough

The USDA’s Dietary Guidelines consistently lists magnesium as a “nutrient of public health concern” because surveys show a large fraction of Americans fall below recommended intake, which is 320-420mg/day for adults.

The reason is mostly about food choices. Magnesium is concentrated in nuts, seeds, legumes, whole grains, and dark leafy greens. These are foods that have been systematically removed from the Western diet and replaced with refined grains, processed meats, and packaged snacks.

Refining wheat into white flour removes roughly 75% of the magnesium. It’s in the bran and germ, which get stripped away. Fortification programs add back iron and B vitamins, but not magnesium.

On top of that, intensive modern agriculture and depleted soils mean that even the vegetables people eat contain less magnesium than they did decades ago. This is documented but the effect size is debated. What’s not debated is that most people eat too few of the foods that contain it in the first place.

Magnesium and Sleep

The sleep research is interesting and increasingly cited, though the quality of evidence is moderate rather than strong.

Magnesium appears to affect sleep through two pathways. First, it supports the production of melatonin by acting as a cofactor in its biosynthesis. Second, its NMDA-blocking action reduces neural excitability, which may make it easier to fall asleep.

A small RCT by Rondanelli et al. (2011, J Am Geriatr Soc) found that a combination of magnesium, melatonin, and zinc improved sleep quality in older adults with insomnia. Isolating magnesium’s specific contribution from this trial is difficult. Other trials using magnesium alone have shown modest improvements in sleep efficiency and insomnia scores. None of the studies are large, and most have methodological limitations.

The honest answer: the evidence suggests magnesium may help with sleep quality, particularly in people who are deficient. For people with already-adequate intake, the effect is probably smaller.

Forms and Bioavailability

Not all magnesium supplements deliver magnesium equally. The difference between forms is significant (Schuchardt & Hahn, 2017, Curr Nutr Food Sci).

Magnesium oxide is cheap to produce and shows up in the majority of budget supplements. Absorption is around 4%, which is poor. The kidneys will excrete most of what you take, and you’ll likely experience digestive side effects at high doses.

Magnesium glycinate pairs magnesium with the amino acid glycine. Absorption is substantially higher. Glycine itself has calming properties and may contribute to the sleep benefits some people report. This is the form most often recommended when the goal is supplementing without gastrointestinal issues.

Magnesium citrate absorbs well and is commonly used as a laxative at high doses. At moderate doses (100-200mg), it’s a reasonable supplement option. Just be aware that it can speed up gut transit.

Magnesium malate and magnesium threonate have specific claims (malate for muscle soreness, threonate for brain penetration), but the supporting evidence is thinner. Threonate has shown promise in animal models for cognitive function, but human data is limited.

Food sources are always preferable to supplements for most nutrients. Pumpkin seeds lead the list with about 150mg per ounce. Dark chocolate (70%+ cacao), almonds, black beans, spinach, and avocado are all strong sources. A diet that includes a good handful of nuts or seeds daily plus legumes several times a week gets most people reasonably close to their magnesium needs.

This article is for educational purposes only. It’s not medical advice. Talk to your doctor or a registered dietitian before making significant changes to your diet.

If you’re reading this because you’re curious about how nutrients are absorbed in general, bioavailability explains the underlying mechanisms. Magnesium’s role in energy metabolism connects closely to how cells produce and use ATP, which is part of the story in metabolic rate science.