Patients often bring in a magnesium supplement and ask whether the dose is right. It is a reasonable question, but usually the wrong one. The number on the label tells you how much elemental magnesium is in the product. It does not tell you how much of it you will absorb, how your gut will tolerate it, or where in the body it will end up.
That is determined by the form, meaning what the magnesium is bound to. And the forms behave differently enough that two products with identical milligram counts can produce very different results.
Magnesium on its own is poorly absorbed. To be usable it gets combined with another compound, often an amino acid or an organic acid, and that partner compound shapes how the mineral behaves in the digestive tract and beyond.
Magnesium itself is involved in an unusually wide range of physiology: energy production, protein synthesis, nerve signaling, muscle contraction and relaxation, bone maintenance, and cardiac rhythm among them. Given that range, it is worth getting the delivery right.
Glycinate (also sold as bisglycinate). Magnesium bound to the amino acid glycine. These two names describe the same compound, so there is no need to agonize over the distinction; “bis-” simply denotes two glycine molecules. It is well absorbed and tends to be gentle on the stomach, which makes it a common choice for daily use. Glycine has its own calming activity in the nervous system, which is part of why this form is often taken in the evening.
Citrate. Magnesium with citric acid. Also well absorbed, but it draws more water into the intestine and has a more pronounced laxative effect. That is a drawback for routine daily supplementation and an advantage if constipation is the thing you are addressing.
Oxide. Widely sold and inexpensive, with a high proportion of elemental magnesium by weight. That high number is misleading, because absorption is poor relative to more soluble forms. NIH data places it below glycinate, citrate, chloride, and lactate on bioavailability. It is frequently used specifically for its laxative effect.
Threonate. Bound to threonic acid. Notable for crossing the blood-brain barrier more readily than other forms, which is why it appears in products aimed at cognitive support rather than general repletion.
There is no universally superior form. The useful question is what you want it to do.
Magnesium also does not operate alone. Its interaction with vitamin D and calcium is directly relevant to bone and muscle health, which is worth accounting for if you are supplementing several things at once.
Magnesium is generally well tolerated, but it is not universally appropriate. Reduced kidney function meaningfully changes magnesium handling and raises the risk of accumulation. Magnesium can also interfere with the absorption of certain medications, including some antibiotics and thyroid medication, where timing matters.
If you take prescription medication, have kidney disease, or are supplementing to address a specific symptom rather than general wellness, bring it up at your next visit. Serum magnesium is a limited test, but in the right clinical context it is worth checking, and we can help you decide whether supplementation makes sense and which form fits your situation.
Source: Thorne Take 5 Daily
