Which Magnesium to Choose? A Guide Based on Updated Research

Standing in front of the supplement shelf, "magnesium" is never just one word: bisglycinate, citrate, marine sucrosomial, oxide, supreme, malate, threonate. They sound like synonyms, but they aren't. They differ in how well they're absorbed and how well they're tolerated.

Be careful, though, about a very common misconception: contrary to how they're often marketed, the various forms of magnesium don't have different uses — there's no "magnesium for sleep" and "magnesium for sport". Magnesium as a nutrient performs the same functions regardless of its chemical form. What really distinguishes the forms is how much of it is absorbed and how well it's tolerated. It's on this level — not on supposed "purposes" — that the choice is made.

This guide compares the main types of magnesium based on absorption data, explains how to really assess your own magnesium status, and when to take it. If you're weighing up several supplements, our guide on when to take supplements may also be useful.

Why magnesium deficiency is so widespread

Epidemiological data show that a significant percentage of the Western population doesn't reach the recommended daily magnesium intake. According to the National Health and Nutrition Examination Survey (NHANES), this situation is correlated with various complaints. Remember that a varied, balanced diet and a healthy lifestyle are always fundamental for overall wellbeing.

Stress and magnesium: a two-way relationship. Scientific literature has documented a complex relationship between stress and magnesium, often described as a "vicious circle". Magnesium is involved in numerous biochemical reactions and plays an important role in regulating the physiological systems involved in the stress response: during tense situations, the body activates response systems that can affect mineral balance. If this sounds like you, you may also be interested in how to manage cortisol and stress.

Modern nutritional impoverishment. Alongside changes in lifestyle, there has been a gradual impoverishment of the magnesium content in food:

• Changes in agriculture: modern farming and changes in soil composition have affected the mineral content of plant-based foods.

• Processing: industrial processing tends to reduce naturally occurring magnesium.

• Evolving dietary habits: the Western diet often favors processed foods over those naturally rich in magnesium, such as leafy greens, whole grains, and nuts.

The contemporary nutritional paradox. This has created a paradox: on one hand a reduction in dietary magnesium intake, and on the other lifestyles that may increase the need for it, along with greater losses linked to various factors of modern life.

What magnesium is for: the authorized claims

Magnesium is an essential mineral: the body doesn't produce it and must obtain it from food. It's involved in hundreds of enzymatic reactions. Unlike many other ingredients, magnesium has the advantage of having officially authorized health claims — statements verified by authorities, not advertising promises. They are as follows:

• Magnesium contributes to the reduction of tiredness and fatigue

• Magnesium contributes to electrolyte balance

• Magnesium contributes to normal energy-yielding metabolism

• Magnesium contributes to the normal functioning of the nervous system

• Magnesium contributes to normal muscle function

• Magnesium contributes to normal psychological function

• Magnesium contributes to normal protein synthesis

• Magnesium contributes to the maintenance of normal bones

• Magnesium contributes to the maintenance of normal teeth

• Magnesium plays a role in the process of cell division

In Italy and the European Union

Health claims are governed by Regulation (EC) 1924/2006 and, for the list of permitted ones, by Regulation (EU) 432/2012. The claims listed above are the ones authorized for magnesium: they can only be used for products that are at least a source of magnesium, meaning they provide at least 15% of the reference nutrient value per serving.

In Switzerland

The Swiss framework, while independent, arrives at the same result: the permitted claims are listed in Annex 14 of the FDHA Ordinance on Food Information (LIV) and, as clarified by the FSVO, are based on European Union provisions. Anyone wishing to use a claim not on that list must apply for individual authorization from the FSVO, which grants it only if the effect is scientifically proven and the consumer isn't misled (authorization procedure — FSVO). The claims apply to products that are at least a source of magnesium under Annex 13 number 28.

In practice: the list is the same on both sides of the border. What differs, as we'll see, are the reference values and the limits in supplements.

How much magnesium per day: reference values

Here Italy and Switzerland diverge, and it's useful to know this:

The reference nutrient value (RNV) — 375 mg — is the value you'll find on the label as a percentage, and it's identical in both countries because it derives from European labeling regulations. Recommended intakes, on the other hand, are set at the national level: in Italy the LARN from the Società Italiana di Nutrizione Umana indicate 240 mg per day for adults, while Swiss reference values (aligned with EFSA) speak of 300 mg for women and 350 mg for men.

The most relevant difference in practice concerns supplements: Switzerland sets 250 mg per day as the additional intake considered safe (beyond what's obtained from food), while in Italy the Ministry of Health allows up to 450 mg. In both cases the same golden rule applies: follow the dose indicated on the label of the product you have in hand, which is already calibrated for the market it's sold in.

How much magnesium actually gets in: absorption and bioavailability

The recommended intakes seen above are calculated based on a mass balance: how much elemental magnesium is needed, on average, to maintain homeostasis in a healthy population. That's a useful number for dietary planning, but it says little about the real performance of a supplement, because it doesn't account for three variables that determine what happens after ingestion:

1. The actual intestinal absorption rate of the chosen chemical form;

2. The systemic bioavailability, meaning how much of that absorbed magnesium remains available for tissues after the first metabolic pass;

3. The transport to the receptor site, far from a given, since there are specific tissue barriers (particularly the blood-brain barrier) that some forms cross better than others.

A systematic review published in Nutrition, which analyzed 14 studies selected from an initial pool of 433, concluded that inorganic magnesium formulations are generally less bioavailable than organic ones, and that the absorption percentage is dose-dependent: it decreases as the dose administered in a single intake increases. This is an important and often underestimated finding: it's worth avoiding a single high-dose daily intake, because it quickly saturates active transcellular transport (TRPM6/TRPM7 channels). Absorption is indicatively 65-70% at low doses (~50 mg) and drops to 20-30% at high doses (>300-400 mg). The authors also note that almost all supplements can maintain physiological levels in healthy individuals without pre-existing deficiencies, but this guarantee doesn't automatically hold for people with conditions that alter absorption (Pardo et al., 2021, Nutrition).

In other words: the label tells you how much elemental magnesium the capsule contains. It doesn't tell you how much of it will actually reach the bloodstream, and even less how much will reach the tissue of interest.

Effects of the unabsorbed portion. Unabsorbed magnesium remains in the intestinal lumen and exerts an osmotic effect, drawing water along a gradient. It's the same principle behind osmotic magnesium laxatives (hydroxide, citrate), and it can result in osmotic diarrhea, abdominal cramps, flatulence, and bloating. In cases of very high and prolonged doses in people with impaired kidney function, there's also a risk of hypermagnesemia — a different mechanism, linked to excess absorption. The extent of these effects varies significantly depending on the bioavailability of the form used: it's no coincidence that the threshold beyond which magnesium preparations can have a laxative effect is indicatively above 250 mg per daily dose.

The advantage of highly bioavailable forms. Better-absorbed forms allow lower dosages while maintaining a good nutritional profile. The advantages are concrete: better tolerability (lower dosages reduce the risk of laxative effects), greater compliance (fewer capsules to take), a safety profile that stays well below the maximum permitted limits, and better nutritional efficiency.

Comparing types of magnesium

The chemical form magnesium is bound to changes its absorption and tolerability. The table compares the forms on verifiable practical characteristics, not on supposed uses: as mentioned, magnesium as a nutrient performs the same functions regardless of form.

Marine sucrosomial magnesium

Marine magnesium is obtained from seawater through sustainable processes and naturally contains trace minerals in proportions developed by nature; the marine matrix provides cofactors that may support magnesium utilization. In its sucrosomial form, the magnesium is encapsulated in a phospholipid matrix (the "sucrosome") that protects it during gastrointestinal transit and improves absorption and tolerability. This is the delivery matrix mentioned above: it doesn't change the elemental magnesium, it changes how much of it gets through.

Magnesium bisglycinate

This is the chelated form, in which magnesium is bound to two molecules of the amino acid glycine. The bond makes it bioavailable and gentle on the digestive tract: it doesn't have the laxative effect typical of other forms, an advantage for people with a sensitive gut or taking higher doses. It's also the single most-searched form among people researching online. It should be noted, however, that in the comparative study below, bisglycinate showed lower increases in magnesium concentration than the sucrosomial form.

Magnesium citrate

Bound to citric acid, this is one of the most widely used forms: highly soluble and with a good level of absorption. It has a mild laxative effect, which can be a pro if you're also looking for support for bowel regularity, or a con if you have a sensitive gut.

Oxide, malate, supreme, and other forms

Magnesium oxide, the most common form in commercial products, contains a lot of magnesium per dose but is poorly absorbed: much of it passes through the gut with a marked laxative effect. Magnesium malate contains malic acid, involved in cellular energy metabolism. Magnesium supreme is magnesium carbonate plus citric acid, which becomes citrate when dissolved in water. Among the niche forms: threonate, the only one with data on crossing the blood-brain barrier and the subject of recent studies on memory and sleep (research data, not a usage indication); taurate, with recent clinical literature limited relative to its notoriety; chloride and pidolate, both highly soluble.

Comparing absorption data: what the study shows

A randomized clinical trial measured the percentage change in magnesium concentration in the 24 hours following a single oral administration of different formulations, in healthy volunteers, comparing marine sucrosomial magnesium with citrate, oxide, and bisglycinate. Three compartments were analyzed: blood, red blood cells, and urine.

Change in magnesium concentration 24 hours from baseline, single dose. Source: Rondanelli M. et al., Eur Rev Med Pharmacol Sci 2018;22(6):1843-1851. Data refer exclusively to the cited study.

In the head-to-head comparison, the sucrosomial form showed the greatest increase in all compartments analyzed: in blood, the increase was 2.1 times higher than bisglycinate, in red blood cells over 2.6 times, in urine 3.1 times.

Two necessary clarifications, to read this data honestly. First: this is a single-dose study in healthy volunteers, which measures concentration changes — not long-term clinical effects. Second, and even more important: this information relates to the results of a scientific study and should not be understood as health claims under the FDHA Ordinance on Food Information (LIV). Research on individual molecules and label-usable claims remain two separate levels — a principle that applies to every form of magnesium, including our own.

A second clinical study confirmed a faster increase in magnesemia with the sucrosomial form compared to magnesium pidolate, in a population with confirmed deficiency (Stefanelli et al., 2023, Journal of Clinical Medicine).

Is magnesium safe? The regulatory status of the various forms

The different forms of magnesium don't enjoy the same regulatory status, and that's not a bureaucratic detail: it reflects the depth (or absence) of long-term safety data evaluated by authorities.

In the European Union, Directive 2002/46/EC establishes in Annex II the closed list of mineral forms permitted in supplements: if a form isn't on that list, it can't be marketed as a source of magnesium, unless authorized as a novel food through a dedicated EFSA assessment. Two recent cases illustrate this:

• Magnesium L-threonate received European authorization as a novel food in October 2024 and was added to Annex II in November 2025. EFSA made the authorization conditional on a maximum intake cap, excluding pregnant and breastfeeding women.

• In the same period, magnesium orotate dihydrate instead failed the EFSA safety assessment and was not authorized: anyone wishing to use it must submit new toxicological data.

The principle useful for consumers: the fact that a form of magnesium is sold online (perhaps imported from non-EU markets) doesn't equate to a European safety judgment. Some forms have circulated for decades with extensive documented human consumption (citrate, oxide, chloride, basic salts); others, like newly synthesized chelates or patented complexes with organic acids, have only a few years of regulatory documentation behind them, however solid it may be.

The specific status in Switzerland

The Swiss framework isn't a photocopy of the European one, but follows a principle of active harmonization. On novel foods, the FSVO clarifies that new foods authorized by the EU are generally marketable in Switzerland too, provided they meet the requirements of Annex 1 of the ordinance on novel foods; the official FSVO list, updated as of February 25, 2026, explicitly includes magnesium L-threonate. On permitted substances, the FDHA Ordinance on the addition of vitamins, minerals, and other substances to food (OAVM, SR 817.022.32) requires that only forms bioavailable to the human body may be added, and sets the threshold for additional magnesium intake beyond diet at 250 mg/day. The maximum dose for supplements remains 375 mg per recommended daily dose.

On the communication front, the constraint is even stricter: supplements can't have a pharmacological effect, nor be presented as medicines or advertised with claims of curing, alleviating, or preventing disease. The only usable health claims are those in Annex 14 LIV or those authorized by the FSVO.

Tests and analyses: how to really assess magnesium levels

The standard blood magnesium test. Blood magnesium is often ordered alongside other electrolytes (calcium, potassium, sodium) to assess overall mineral balance. It has a structural limitation, though: only 1-2% of the body's magnesium is found in the blood, while 98-99% is distributed in bones, muscles, and tissues. Standard tests therefore only provide a rough estimate of actual status. The body also keeps blood magnesium stable within a narrow range by drawing on bone reserves and regulating renal excretion, even when intracellular reserves have already started to decline: this is why blood magnesium, while remaining the most commonly used clinical parameter, often fails to detect subclinical deficiency (Rondón & Marín, 2026, Advances in Clinical Chemistry).

A doctor might order the test in cases of: symptoms like persistent fatigue, muscle cramps, or irritability; changes in calcium or potassium in previous tests; conditions that may affect absorption (gastrointestinal disease); monitoring during supplement use; assessment of overall electrolyte balance.

Alternative tests for more accurate assessment.

• 24-hour urinary magnesium: provides information on renal excretion and is useful for assessing magnesium balance over time; requires collecting all urine over 24 hours.

• Red blood cell magnesium (RBC magnesium): may better reflect tissue reserves than serum magnesium and is considered more representative of intracellular status; not available at all laboratories.

• Magnesium loading test (only under medical supervision): involves controlled administration of magnesium followed by measurement of urinary excretion. Used mainly in specialist settings and can help identify subclinical deficiencies.

Test preparation. Blood magnesium generally doesn't require fasting; for urinary magnesium, specific collection instructions must be followed. Always inform your doctor of all medications and supplements you're taking, and follow the laboratory's instructions.

Complementary nutritional assessment. Besides testing, it's useful to consider dietary intake (leafy greens, nuts, whole grains), factors that increase requirements (prolonged stress, intense physical activity, heavy sweating), and conditions that reduce absorption (gastrointestinal disorders, certain medications, older age).

When and how to take magnesium

Beyond the form, timing and manner of intake also matter — though it should be said that scientific research specifically on the optimal timing of magnesium intake is, to date, rather limited: the following recommendations are based more on general tolerability principles than on trials specifically comparing different times of day.

• When: magnesium can be taken at any time of day, preferably during or after a meal to improve gastrointestinal tolerability. Forms like marine sucrosomial or bisglycinate, well tolerated even on an empty stomach, lend themselves well to an evening routine — not because they're more effective at that time of day, but because they don't interfere with nighttime rest through possible gut discomfort. Some researchers propose, based on synthesizing studies on individual circadian mechanisms, that there's a window in the late afternoon (indicatively between 3pm and 8pm) in which the body might use magnesium particularly efficiently ahead of nighttime anabolic processes. For now this is a synthesis hypothesis, not a finding confirmed by a dedicated study: it will be important to follow developments.

• How: higher single doses tend to have a lower absorption percentage than smaller doses; splitting the daily dose into two intakes, when it's high, is therefore consistent with this principle, as well as useful for tolerability. Drink enough water, especially if the chosen form has a laxative effect.

• How much: always follow the label instructions and don't exceed the recommended daily dose. The reference nutrient value on the label is 375 mg (including dietary intake); limits for supplements differ between Italy and Switzerland, as seen above.

Combinations. Magnesium fits well into a complete wellness routine. Combining it with vitamin D has a solid scientific rationale, not just a practical one: vitamin D promotes intestinal absorption of magnesium, while magnesium in turn is needed to activate vitamin D in the body — a mutually dependent relationship documented in the literature, in addition to vitamin D's own independent contribution to normal muscle function (Dominguez et al., 2025, Nutrients). Prebiotic fibers like inulin, too, according to a systematic review of human studies, promote the absorption of calcium and magnesium through gut fermentation by the microbiome (Hughes et al., 2023, Advances in Nutrition) — a different mechanism from that of the delivery matrix, but pointing in the same direction: the context in which magnesium is taken matters as much as the chemical form itself. It's worth keeping in mind, though, that some compounds compete with magnesium for the same absorption pathways — particularly phytates from whole grains, legumes, and seeds: if you're already taking a supplement rich in phytic fiber or a high-dose calcium multivitamin, it's useful to space out intakes across the day.

NIGHTRELAX: marine sucrosomial magnesium and synergistic formulation

NIGHTRELAX by Swiss Natural Med is born from combining the natural origin of marine magnesium with sucrosomial technology: the ocean's matrix, with its trace minerals, delivered in a phospholipid matrix that protects its transit and improves absorption and tolerability. This is the form whose comparative absorption data you saw above.

But NIGHTRELAX isn't just magnesium: it's a synergistic formulation, combining the mineral with other selected ingredients.

• Saffron (Crocus sativus) — research has studied saffron's active compounds and their effects on neurotransmitter systems.

• Hawthorn (Crataegus) — the extracts contain flavonoids and oligomeric procyanidins, the subject of clinical research.

• B vitamins from plant fermentation — B1, B6, and B12 work synergistically with magnesium in numerous enzymatic reactions of energy metabolism and in neurotransmitter synthesis.

Thanks to the high bioavailability of the sucrosomial form, NIGHTRELAX allows working with lower dosages while maintaining a good nutritional profile: better tolerability, fewer capsules to take, and a wide margin relative to the maximum permitted limits. Magnesium contributes to the normal functioning of the nervous system, to normal psychological function, to normal muscle function, and to the reduction of tiredness and fatigue — with the quality and traceability that characterize Swiss Natural Med's Swiss formulation.

For even more complete evening wellness support, you can pair it with SerenDay.

The information in this article is for educational purposes and doesn't replace the advice of a doctor or healthcare professional. Food supplements don't replace a varied, balanced diet and a healthy lifestyle. In case of pregnancy, breastfeeding, medication use, or particular conditions, consult a doctor before use.

By Derry Procaccini — Swiss Natural Med.

Frequently asked questions

What's the difference between marine sucrosomial magnesium and bisglycinate?

They're two different strategies for improving magnesium absorption: bisglycinate does it by changing the chemical nature of the salt (chelation with glycine), sucrosomial does it by protecting the salt with an outer matrix that modulates its intestinal release (encapsulation). A crossover study in healthy volunteers found, after administration of the same dose, significantly higher red blood cell magnesium concentration with the sucrosomial form compared to bisglycinate (Brilli et al., 2018, European Review for Medical and Pharmacological Sciences) — a relevant finding because intra-erythrocyte concentration is considered, in the literature, a more direct indicator of intracellular magnesium reserves than blood magnesium alone, which the body tends to keep stable even in the presence of initial tissue deficiency.

Which magnesium is most absorbable?

There's no single answer that's absolutely valid. Among the best-absorbed forms are chelates like bisglycinate and delivery-matrix formulations like marine sucrosomial, which has comparative human absorption data. Oxide, by contrast, is poorly absorbed. Dose matters too: the highest absorption percentages are seen with smaller doses.

Bisglycinate or citrate: which to choose?

It mainly depends on tolerability. Bisglycinate has no laxative effect, so it's convenient at higher doses or in the evening; citrate has a mild laxative effect, which can be useful if you're also looking for support with bowel regularity, or a downside if you have a sensitive gut.

When is it best to take magnesium, morning or evening?

It can be taken at any time, preferably with meals. Forms well tolerated even on an empty stomach lend themselves to the evening because they don't disturb rest — not because they're more effective at that time. Research on optimal timing is still limited.

Are blood tests enough to detect magnesium deficiency?

Not entirely. Only 1-2% of the body's magnesium is found in blood: blood magnesium is a poorly sensitive indicator and may fail to detect a subclinical deficiency. Alternative tests exist (24-hour urinary magnesium, red blood cell magnesium, loading test), always to be evaluated with a healthcare professional.

What's the daily dose of magnesium?

The reference nutrient value on the label is 375 mg per day, including dietary intake. Recommended intakes vary: in Italy the LARN indicate 240 mg per day for adults, in Switzerland the figures are 300 mg for women and 350 mg for men. Supplement limits also differ: 450 mg/day in Italy, 250 mg/day in Switzerland. Always follow the label instructions of the product you're using.

Does magnesium have contraindications?

For most people it's well tolerated. High doses, especially of poorly absorbed forms, can have a laxative effect. In case of kidney insufficiency, medication use, or particular conditions, it's advisable to consult a doctor before use.

Scientific bibliography

• Pardo MR et al. Bioavailability of magnesium food supplements: A systematic review. Nutrition, 2021.

• Aniebo Umoh E et al. Effect of chronic administration of magnesium supplement (magnesium glycinate) on rat intestinal motility. Heliyon, 2023 (preclinical study in a mouse model).

• Zhang C et al. A Magtein, Magnesium L-Threonate, -Based Formula Improves Brain Cognitive Functions in Healthy Chinese Adults. Nutrients, 2022.

• Hausenblas HA et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems. Sleep Medicine: X, 2024.

• Brilli E et al. Magnesium bioavailability after administration of sucrosomial magnesium: results of an ex-vivo study and a comparative, double-blinded, cross-over study in healthy subjects. European Review for Medical and Pharmacological Sciences, 2018.

• Rondanelli M et al. Percent Changes in Magnesium Concentrations in Serum, Red Blood Cells, and Urine After a Single Oral Dose of Sucrosomial Magnesium Compared to Those of Other Magnesium Formulations. European Review for Medical and Pharmacological Sciences, 2018;22(6):1843-1851.

• Stefanelli LF et al. Calcineurin-Inhibitor-Induced Hypomagnesemia in Kidney Transplant Patients: A Monocentric Comparative Study between Sucrosomial Magnesium and Magnesium Pidolate Supplementation. Journal of Clinical Medicine, 2023.

• Dominguez LJ et al. The Importance of Vitamin D and Magnesium in Athletes. Nutrients, 2025.

• Hughes RL et al. The Prebiotic Potential of Inulin-Type Fructans: A Systematic Review. Advances in Nutrition, 2023.

• Rondón & Marín. Advances in Clinical Chemistry, 2026.

Regulatory sources

• Directive 2002/46/EC and subsequent amendments, Annex II — EUR-Lex.

• Commission Implementing Regulation (EU) 2024/2694 of 17 October 2024 — authorization of magnesium L-threonate as a novel food.

• FSVO — List of "novel foods and food ingredients that may be placed on the market in accordance with Regulation (EC) No 258/97 and 2015/2283", as of 25 February 2026.

• FDHA Ordinance of 16 December 2016 on Food Supplements (OIAI, SR 817.022.14).

• FDHA Ordinance of 16 December 2016 on the addition of vitamins, minerals and other substances to foodstuffs (OAVM, SR 817.022.32).

• FDHA Ordinance on Food Information (LIV) — Annex 14.

• FSVO/BLV — Authorization for health claims (blv.admin.ch).

• Regulation (EC) 1924/2006 on nutrition and health claims made on food.

• Regulation (EU) 432/2012 — list of permitted health claims made on foods.

• LARN — Reference Intake Levels of Nutrients and Energy for the Italian population, SINU.

• Ministry of Health (Italy) — Maximum daily intakes of minerals in food supplements.