If you could only recommend one supplement to the general population, there is a strong argument for magnesium. Not because it is exciting or trendy, but because the gap between how much most people need and how much they actually consume is enormous. Magnesium is involved in over 300 enzymatic reactions in the body, and somewhere between 40-60% of adults in developed countries do not meet the recommended dietary intake. This is not a niche deficiency. It is a widespread nutritional gap with measurable health consequences.

Why magnesium deficiency is so common

The recommended dietary allowance for magnesium is 310-320mg for women and 400-420mg for men. The average American adult consumes roughly 260mg per day -- consistently below the RDA across multiple NHANES surveys spanning decades.

Several factors drive this gap. Modern agricultural practices have depleted soil magnesium levels, reducing the magnesium content of crops over the past century. Water treatment removes magnesium that historically contributed to dietary intake. Processed food diets are inherently low in magnesium -- refined grains lose approximately 80-95% of their magnesium content during processing. And chronic stress, alcohol consumption, and several common medications (proton pump inhibitors, diuretics, certain antibiotics) actively deplete magnesium stores.

A 2018 review in Open Heart characterized subclinical magnesium deficiency as a "principal driver of cardiovascular disease and a public health crisis." The authors argued that standard serum magnesium tests -- the ones most doctors order -- miss the vast majority of deficiency cases because only 1% of total body magnesium is in the blood. Intracellular magnesium testing (RBC magnesium) is more accurate but rarely ordered in routine practice.

What magnesium does in your body

Magnesium is not a single-function mineral. It is a cofactor in ATP production (every molecule of ATP must be bound to magnesium to be biologically active), DNA and RNA synthesis, protein synthesis, muscle contraction and relaxation, nervous system regulation, blood glucose control, and blood pressure regulation. Deficiency manifests in ways that are often attributed to other causes: muscle cramps, insomnia, anxiety, headaches, fatigue, irregular heartbeat, and constipation.

A 2017 scientometric analysis in Scientometrics mapped the magnesium research landscape and identified over 12,000 published studies. The evidence connecting magnesium status to cardiovascular health, metabolic function, neurological health, and musculoskeletal function is extensive and consistently directional.

The form problem: not all magnesium is equal

This is where most consumers go wrong. "Magnesium" is an element that must be bound to another molecule (a "chelate" or salt) for oral supplementation. The form determines absorption, bioavailability, and which specific benefits you experience. Choosing the wrong form means spending money on magnesium that either is not absorbed or does not reach the tissues you are targeting.

Magnesium Glycinate (Bisglycinate)

Best for: sleep, anxiety, general supplementation

Magnesium glycinate binds elemental magnesium to glycine, an amino acid that itself has calming and sleep-promoting properties. The absorption rate is excellent -- roughly 20-25% bioavailability compared to 4% for magnesium oxide. The glycine chelation protects the magnesium from interacting with phytates and other absorption inhibitors in the gut.

A 2012 study in the Journal of Research in Medical Sciences found that magnesium supplementation significantly improved insomnia severity index scores, sleep efficiency, sleep time, and early morning awakening in elderly subjects. While the study used magnesium oxide, the benefits are more consistently achieved with better-absorbed forms like glycinate.

The glycine component is itself an active sleep ingredient. As discussed in our sleep supplements article, glycine at 3g before bed has independent evidence for improving sleep quality by lowering core body temperature. While the glycine in magnesium glycinate supplements is typically less than 3g (usually 1-1.5g from 200-300mg elemental magnesium doses), it provides additive benefit.

Magnesium glycinate causes minimal GI distress compared to other forms, making it the best general-purpose option for most people. If you are choosing one form without a specific therapeutic target, glycinate is the default recommendation.

Magnesium L-Threonate (Magtein)

Best for: cognitive function, brain health, neuroprotection

Magnesium L-threonate is the only form with specific evidence for crossing the blood-brain barrier and increasing brain magnesium levels. It was developed by MIT researchers (Guosong Liu et al.) and is sold under the Magtein brand name.

A 2010 study in Neuron demonstrated that magnesium threonate increased brain magnesium levels by 15% in animal models, while other forms did not significantly alter brain magnesium. This translated to enhanced synaptic plasticity and improved short-term and long-term memory. A 2016 human clinical trial in the Journal of Alzheimer's Disease found that older adults taking Magtein showed significant improvements in cognitive ability compared to placebo, with brain age effectively reduced by 9 years on cognitive testing.

The downside: magnesium threonate provides relatively low elemental magnesium per capsule (approximately 48mg per 2g dose). If you are addressing a significant whole-body magnesium deficiency, threonate alone may not be sufficient. Many practitioners recommend combining threonate (for brain-specific benefits) with glycinate (for overall magnesium repletion).

Magnesium threonate is also the most expensive form, typically $25-35 per month. The premium is justified if cognitive health is your primary concern, less so for general supplementation.

Magnesium Citrate

Best for: constipation, general supplementation on a budget

Magnesium citrate has reasonable bioavailability (roughly 16-20%) and is significantly cheaper than glycinate or threonate. The citric acid component has a mild osmotic laxative effect, which is beneficial if constipation is one of your symptoms and counterproductive if it is not.

A 2017 study in Magnesium Research compared magnesium citrate to magnesium oxide and found significantly higher bioavailability for the citrate form. For general magnesium repletion in someone who tends toward constipation, citrate is an efficient and economical choice.

The laxative effect is dose-dependent. At 200-300mg elemental magnesium, most people tolerate citrate well. At 400mg+, loose stools become common. If GI sensitivity is a concern, glycinate is the better option.

Magnesium Oxide

Best for: nothing, frankly

Magnesium oxide is the most common and cheapest form of magnesium supplement. It is also the worst. With approximately 4% bioavailability, a 400mg magnesium oxide capsule delivers roughly 16mg of usable magnesium. You would need to take enormous quantities to achieve meaningful repletion, and the GI side effects (primarily diarrhea) make that impractical.

A 2001 study in the Journal of the American College of Nutrition directly compared magnesium oxide to magnesium citrate and found oxide absorption was "significantly lower." Magnesium oxide is essentially an expensive laxative with minimal supplemental value. If your current magnesium supplement is oxide-based, switching to glycinate or citrate is one of the highest-value changes you can make.

Magnesium Malate

Best for: muscle pain, fatigue, fibromyalgia

Magnesium malate combines magnesium with malic acid, which plays a role in the Krebs cycle (cellular energy production). There is preliminary evidence suggesting benefit for fibromyalgia-related pain and fatigue, though the research is limited. A 1992 pilot study in the Journal of Nutritional Medicine found reduced pain and tenderness scores in fibromyalgia patients taking magnesium malate. Bioavailability is good, and it is generally well tolerated.

Evidence for specific conditions

Sleep: A 2021 systematic review in BMC Complementary Medicine and Therapies found that magnesium supplementation was associated with significant improvements in subjective sleep quality, particularly in populations with low dietary magnesium intake. The evidence is strongest for glycinate and threonate forms.

Anxiety: A 2017 systematic review in Nutrients found that magnesium supplementation had a beneficial effect on subjective anxiety, with the strongest effects in individuals with insufficient magnesium intake. The evidence is moderate but consistent across multiple studies.

Migraine prevention: A 2016 systematic review in Headache found that magnesium supplementation (typically 400-600mg daily) reduced migraine frequency by approximately 40% compared to placebo. The American Academy of Neurology and the American Headache Society include magnesium in their evidence-based guidelines for migraine prophylaxis. This is one of the strongest evidence-based applications for magnesium supplementation.

Muscle cramps: The evidence here is actually more nuanced than expected. While magnesium deficiency can cause cramps, a 2020 Cochrane review found that magnesium supplementation did not significantly reduce cramp frequency or intensity in the general population. However, it did show benefit in pregnant women experiencing cramps and in individuals with documented deficiency. The takeaway: magnesium helps cramps if your cramps are caused by magnesium insufficiency, which is common but not universal.

Practical recommendations

For general health and sleep: magnesium glycinate (bisglycinate) at 200-400mg elemental magnesium, taken in the evening. For cognitive function and brain health: add magnesium L-threonate (Magtein) at the standard 2g dose (providing 144mg elemental magnesium). For constipation: magnesium citrate at 200-400mg elemental magnesium. For migraine prevention: 400-600mg elemental magnesium daily (glycinate or citrate), ideally split into two doses.

Avoid magnesium oxide unless you specifically want a laxative effect. Ignore products that list "magnesium" without specifying the form -- this almost always means oxide, the cheapest and least effective option.

Magnesium is not glamorous. It does not have slick marketing campaigns or influencer sponsorships. But in terms of evidence strength, prevalence of deficiency, breadth of health benefits, and cost-effectiveness, it may be the single most impactful supplement for the general population. The best part: a quality magnesium glycinate supplement costs roughly $0.15-0.30 per day. For the price of one AG1 subscription, you could supplement magnesium for an entire year.