Magnesium is involved in over 600 processes in the body, including energy production, muscle function, and sleep regulation.
The standard serum magnesium blood test measures only 1% of total body magnesium. Results can appear normal while tissue stores are depleted.
At least 20% of people are clinically low in magnesium; up to 80% may not be getting enough to function well - partly because magnesium content in vegetables has fallen by around 25% since the 1940s due to soil depletion.
Not all supplement forms are equivalent. Magnesium glycinate is the best starting point for sleep and anxiety; citrate works well for digestive sluggishness; L-threonate is designed to cross into brain tissue. Magnesium oxide is poorly absorbed and mainly functions as a laxative.
Introduction
Magnesium doesn't attract the same attention as vitamin D or omega-3s, but it arguably should. It is involved in over 600 enzymatic processes - energy production, muscle contraction, nerve signalling, blood sugar regulation, blood pressure, and protein synthesis among them.
It also has a direct role in sleep. Magnesium helps the body produce melatonin, activates the parasympathetic nervous system, and supports GABA - the neurotransmitter that reduces neuronal excitability and promotes calm. Low magnesium is associated with elevated cortisol, poorer sleep quality, and an increased risk of depression.
For anyone exercising regularly, magnesium helps shuttle blood sugar into muscle cells and clear lactate - which is why deficiency can blunt performance and slow recovery.
The Testing Problem
Here is something worth knowing before you ask your GP to check your levels: the standard serum magnesium test only measures the magnesium circulating in your blood. That is roughly 1% of the body's total magnesium stores. The other 99% sits in bone, muscle, and other tissues, where it is actually doing its job.
The body maintains blood magnesium levels tightly - when tissue stores fall, it draws from bone and muscle to keep the serum reading stable. The result is that you can be genuinely depleted, symptomatic, and still return a 'normal' blood test. As deficiency worsens, symptoms can include muscle cramps, numbness, tingling, abnormal heart rhythms, and - in severe cases - seizures.
At least 20% of the population is clinically deficient; up to 80% may not be getting enough for optimal function, even if their blood work looks unremarkable.
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Magnesium Deficiency
Magnesium deficiency rarely announces itself clearly. It tends to show up as a cluster of symptoms that are easy to chalk up to stress or poor sleep.
What to watch for:
Muscle cramps, particularly in the calves or feet at night, or persistent tension across the neck and shoulders
Difficulty falling asleep or staying asleep - a 'tired but wired' quality, where the body is exhausted but the mind won't settle
Heightened anxiety, emotional reactivity, or a sense that usual coping strategies aren't holding
Difficulty concentrating or brain fog
Constipation, since magnesium is needed for smooth intestinal muscle function
Heart palpitations
Increased sensitivity to noise, light, or caffeine
For people going through hormonal shifts - perimenopause, pregnancy, or fluctuating cycles - these symptoms can be more pronounced, as hormonal changes affect magnesium utilisation.
Why deficiency is now so common:
Several factors have converged to make inadequate magnesium the norm rather than the exception.
Soil depletion: Modern farming has gradually stripped magnesium from agricultural soil. Studies suggest the magnesium content of vegetables has fallen by around 25% since the 1940s - meaning even magnesium-rich foods like spinach and almonds now deliver less than they used to.
Food processing: Refining whole grains into white flour or white rice removes up to 80% of their magnesium. Given how much of the typical Western diet consists of processed foods, many people are eating very little naturally occurring magnesium.
Chronic stress: Stress accelerates magnesium excretion, while magnesium is precisely what the body needs to regulate the stress response. The two deplete each other in a cycle.
Caffeine and alcohol: Both increase urinary magnesium excretion. Occasional use is not a problem, but regular consumption chips away at levels over time.
Medications: Proton pump inhibitors, diuretics, oral contraceptives, and some antibiotics all reduce magnesium absorption or increase excretion.
Gut health: Conditions that impair intestinal absorption - IBS, SIBO, Crohn's disease - can significantly reduce how much dietary magnesium actually makes it into the body.
Getting Magnesium from Food: The Foundation
Food remains the best foundation. These are the most useful sources, with quantities based on a standard serving:
Pumpkin seeds - 28g provides approximately 262mg (around 90% of daily needs)
Brazil nuts - 28g provides 107mg (38%)
Sunflower seeds - 28g provides 91mg (32%)
Swiss chard, cooked - 100g provides 81mg (28%)
Spinach, cooked - 100g provides 79mg (28%)
Cashews - 28g provides 83mg (29%)
Almonds - 28g provides 76mg (27%)
Black beans, cooked - 100g provides 70mg (25%)
Quinoa, cooked - 100g provides 64mg (22%)
Dark chocolate (70%+ cacao) - 28g provides 64mg (22%)
Chickpeas, cooked - 100g provides 48mg (17%)
Brown rice, cooked - 100g provides 43mg (15%)
Lentils, cooked - 100g provides 36mg (13%)
Banana, medium - approximately 32mg (11%)
Avocado, medium - approximately 29mg (10%)
The chlorophyll in green vegetables is itself structured around a magnesium atom, which is why leafy greens are among the most bioavailable dietary sources.
Even with a good diet, many people find it difficult to consistently reach optimal intake - particularly given soil depletion and the effect of modern stressors on magnesium requirements. Supplementation is often a reasonable addition.
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How to Supplement
Supplement forms differ significantly in absorption and effect. The most relevant options:
Magnesium glycinate combines magnesium with glycine, an amino acid with mild calming properties of its own. It is well-absorbed, gentle on the stomach, and is the most practical all-round choice - particularly for sleep, anxiety, and muscle tension. Take 200-400mg around 30-60 minutes before bed.
Magnesium citrate is also well-absorbed and draws water into the intestines, which softens stool. This makes it useful for constipation or digestive sluggishness, but means that too large a dose - or taking it on an empty stomach before you're accustomed to it - can cause loose stools. Start at 150-200mg and adjust.
Magnesium L-threonate was developed specifically to cross the blood-brain barrier more effectively than other forms, with cognitive support as the primary target. Early research suggests benefits for memory, focus, and mental clarity. Some people find it mildly energising; timing (morning vs. evening) is worth experimenting with.
Topical magnesium - oils, creams, or Epsom salt baths - allows absorption through the skin, bypassing the gut entirely. Useful if you have digestive issues that interfere with oral supplements, or for targeted muscle tension. Some people experience mild tingling initially; this typically settles with regular use.
Magnesium oxide is poorly absorbed by design. It functions primarily as a laxative and is not an appropriate choice if your goal is raising body magnesium levels.
Small studies have found that the aspartate, citrate, lactate, and chloride forms are more completely absorbed than oxide or sulphate.
Supporting Absorption
Magnesium works alongside several other nutrients, and deficiency in one can limit the effect of another.
Vitamin D and magnesium are mutually dependent. Magnesium is needed to activate vitamin D, and vitamin D improves magnesium absorption. If you supplement vitamin D without adequate magnesium, you may get limited benefit from either.
Vitamin B6 enhances magnesium uptake at the cellular level. This is particularly relevant for mood and stress support. If you are dealing with both, a B-complex taken alongside magnesium is worth considering.
Calcium and magnesium need to be kept in balance. Both are essential for bone health, but high calcium intake without adequate magnesium can interfere with magnesium function. Severe magnesium deficiency also depresses serum calcium and disrupts potassium levels - a reminder that these minerals regulate each other.
Stress management improves utilisation. This is not simply lifestyle advice. Chronic psychological stress directly increases magnesium excretion. Anything that genuinely reduces baseline stress - consistent sleep, regular moderate exercise, reduced alcohol - helps your body hold on to the magnesium it has.
Where to start
If you are experiencing several of the symptoms described above, start with magnesium glycinate at 200-300mg taken an hour before bed. Give it at least four weeks before assessing the effect - it takes time to rebuild tissue stores.
If you want to know whether deficiency is contributing to your symptoms, a standard serum magnesium test is a reasonable starting point - but bear in mind its limitations. A comprehensive blood panel that includes magnesium alongside other relevant markers gives a clearer picture of where any gaps actually are.
References
Touyz RM, de Baaij JHF, Hoenderop JGJ. Magnesium Disorders. The New England Journal of Medicine. 2024;390(21):1998-2009.
de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in Man: Implications for Health and Disease. Physiological Reviews. 2015;95(1):1-46.
Fiorentini D, Cappadone C, Farruggia G, Prata C. Magnesium: Biochemistry, Nutrition, Detection, and Social Impact of Diseases Linked to Its Deficiency. Nutrients. 2021;13(4):1136.
Pelczyńska M, Moszak M, Bogdański P. The Role of Magnesium in the Pathogenesis of Metabolic Disorders. Nutrients. 2022;14(9):1714.
Barbagallo M, Veronese N, Dominguez LJ. Magnesium in Aging, Health and Diseases. Nutrients. 2021;13(2):463.
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