Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
Vitamin D enters the body inactive and must be converted by liver and kidney enzymes before cells can use it, and those enzymes depend on magnesium to do their work. Keeping magnesium present alongside vitamin D supports the activation step the vitamin relies on.
Calcium drives muscle fibers to contract while magnesium supports the relaxation that follows, so steady muscle and nerve signaling rests on a working balance between the two minerals. They also share intestinal transport, so a very large calcium dose taken alone can compete with magnesium for absorption, which is why formulas keep them in proportion.
The sodium potassium pump that keeps potassium inside cells runs on magnesium bound ATP, and magnesium also helps regulate the kidney channels that decide how much potassium is held versus passed in urine. When magnesium is low the body tends to let potassium slip away, so adequate magnesium supports normal potassium balance.
The kinase that turns vitamin B6 into its active coenzyme form uses magnesium bound ATP as its working substrate, so magnesium supports the step that makes B6 usable in the body. That shared dependence is part of why magnesium and B6 have been formulated together for decades.
Zinc and magnesium share paracellular and carrier-mediated uptake routes, so a large dose of one lowers the other's absorbed fraction. Separating the doses is the standard formulation answer.
Ferrous iron and magnesium compete for the same duodenal uptake routes, so co-dosing large amounts lowers both absorbed fractions. Citrate does raise iron solubility, which is why the interaction can run either way at low doses.
Magnesium citrate is already fairly soluble, but carbonate raises gastric pH and adds a competing divalent cation at the same uptake sites. A large carbonate dose in the same swallow lowers the magnesium fraction absorbed.
Thiamine is converted to thiamine pyrophosphate by a magnesium-dependent kinase, and the enzymes that use the cofactor need magnesium too. A soluble magnesium form supports the whole thiamine step.
Creatine kinase moves a phosphate between creatine and magnesium-bound ATP, so magnesium is part of the reaction rather than an add-on. Citrate is a well-absorbed form for supplying it.
Psyllium forms a viscous gel that traps divalent cations and slows their diffusion to the mucosal surface, lowering the absorbed magnesium fraction from the same dose. Both also draw water into the lumen, so the osmotic effects add.
Magnesium Citrate + TaurineEstablished co-formulation and shared electrolyte handling. A candidate trial studied a magnesium taurate salt. Taurine is used as the counter-ion in magnesium taurate and both compounds appear in the same cardiovascular and neuromuscular formulation category. A randomised trial in the candidate set studied a magnesium taurate with potassium citrate combination on blood pressure and vascular stiffness measures rather than magnesium citrate specifically. The salt studied is not the salt on this page, which is the caveat to carry.
Products often combine two magnesium salts to split the elemental load between a more osmotically active salt and a less osmotically active one. Citrate dissociates readily and draws water into the gut lumen at higher single doses. Glycinate is chelated and does that less. Combining them is a formulation choice about total elemental magnesium and gut tolerance.
Theanine and magnesium appear together in evening formulations on the grounds that magnesium is a cofactor across neuronal energy metabolism while theanine acts on glutamate receptor signalling and alpha wave activity. The two routes do not overlap. No trial has measured the pair.
Melatonin acts through MT1 and MT2 receptors on circadian timing, which is unrelated to magnesium's role as an enzyme cofactor. Products combine them for evening use. Where other sedating agents are already in the routine, the combined effect on alertness the next morning is the thing to watch.
Vitamin K is the cofactor for the carboxylation that lets matrix Gla protein and osteocalcin bind calcium, and magnesium is required for the conversion of vitamin D to its active form. The three appear together in bone formulations for those distinct roles. Anyone on a vitamin K antagonist medicine needs to raise vitamin K intake with their prescriber.
Magnesium and phosphate form poorly soluble complexes in the gut lumen, so large simultaneous doses reduce each other's absorbed fraction. This is the same chemistry that makes magnesium salts useful as phosphate binders. A published trial design in the candidate set sets out to modulate both together in adults with reduced kidney function. Spacing large doses is the practical answer.
Boron appears in mineral nutrition work in relation to how the body handles magnesium and calcium, and it is a routine minor component of bone formulations. The human evidence base is small next to magnesium's. Read it as a supporting mineral at modest confidence.
Fermentable fibres lower colonic pH through short-chain fatty acid production, which keeps magnesium and calcium in solution and supports passive absorption in the large bowel. The effect is measurable but modest next to small intestinal uptake. Combining a fermentable fibre with an osmotically active magnesium salt can also add to gas and stool looseness.
Activated charcoal adsorbs a wide range of compounds in the gut lumen without selectivity, and charcoal appears in the co-occurrence record alongside magnesium citrate in bowel preparation contexts. Taking the two together lowers what is available for absorption. Separating them by several hours is standard practice.
Citrate is metabolised to bicarbonate, so a citrate salt acts as an alkalinising agent and raises urinary citrate excretion, and added bicarbonate pushes urinary pH the same way. Urinary pH and citrate are markers of that handling, not outcomes. Anyone using either under medical direction should keep the combined load in view.
Magnesium oxide carries the highest elemental magnesium per gram of the common salts and dissolves poorly, while citrate carries less elemental magnesium per gram and dissolves readily. Blending them is a formulation approach to fitting a target elemental dose into a given capsule size. Two magnesium products in one routine can also add up past what the gut tolerates in a single sitting.
Magnesium salts need to dissociate before absorption, and the poorly soluble salts depend more on gastric acid to do it than citrate does. Citrate is already comparatively soluble at gastric pH, so the acid dependence is smaller here than for oxide or carbonate. This is chemistry rather than a measured combination.
Riboflavin as FAD and magnesium as the ATP counter-ion both sit inside mitochondrial energy handling, which is the mechanistic reason they are formulated together. A Cochrane review in the candidate set assesses magnesium supplementation on its own, not the combination. The pairing is mechanistic plus formulation convention.
Ubiquinone carries electrons between complexes I and II and complex III, while magnesium is required by the ATP synthase reaction and by every kinase that uses ATP. Both appear in the same energy-support formulations for those separate positions in the same pathway. There is no combination trial.