What exactly does magnesium glycinate do in your body?
Magnesium glycinate is well absorbed, but for most healthy people it is not demonstrably better than citrate. For those with poor intestinal function or a sensitive stomach, it is a worthwhile choice.
Magnesium glycinate is a compound in which magnesium is bound to the amino acid glycine. That binding matters for absorption: the compound is partly taken up as an intact molecule via a dedicated transport route in the small intestine, alongside the ordinary route through which free magnesium ions enter. This distinguishes it from cheaper forms such as magnesium oxide.
For most healthy people, that advantage is smaller than manufacturers suggest. In a comparative study after 60 days, organic forms such as citrate and amino acid chelate (the category that includes glycinate) both outperformed oxide, but citrate produced the highest magnesium blood levels. Glycinate did not perform measurably better than citrate.
Where glycinate does stand out clearly is in people with poor intestinal function, for example after surgery in which part of the small intestine has been removed. In that group, absorption of glycinate was twice as high as that of oxide (23.5% versus 11.8% in the poorest-absorbing patients). The alternative absorption route genuinely helps in those cases. In addition, glycinate was better tolerated than oxide in that study, although this was not substantiated with numerical data.
Magnesium itself plays a role in hundreds of processes in the body, and a chronically low magnesium level is associated with a greater risk of cardiovascular disease and metabolic problems. These are associations from years of public health research, not evidence that supplementation prevents those diseases. One additional pitfall: a normal blood test result for magnesium does not rule out a deficiency. The standard blood test measures only what is circulating in the blood, not the total supply in your tissues.
When choosing a magnesium form, the practice guide points to magnesium citrate as the best-supported choice for absorption in healthy people, with 300 mg of elemental magnesium per day as the most commonly used dose in bioavailability studies and at least 60 days required for a stable effect on blood levels. Glycinate is a reasonable alternative, especially if you experience gastrointestinal complaints with other forms or if your intestinal function is limited. Oxide performs worst in every comparison.
This answer is based on two small randomised studies (one in patients with an intestinal resection, one comparative absorption study in healthy people), supplemented by two review articles on the broader role of magnesium in the body and the reliability of blood tests. The evidence on absorption is reasonable but limited to small groups. For tolerability, only one small study is available, without quantitative data. The broader health associations are based on long-term public health research without a demonstrated causal relationship.
Can magnesium glycinate cause diarrhoea or gastrointestinal complaints?
At normal doses (around 5 mg per kilogram of body weight per day) gastrointestinal complaints are not to be expected, but at higher doses a laxative effect is a well-known side effect of oral magnesium.
Does magnesium glycinate help you sleep better?
Magnesium may offer some benefit for sleep in certain people who are deficient or have a medical condition, but this has not been demonstrated for healthy people without a deficiency. If you have had poor sleep for years, first discuss with your doctor whether other causes may be involved.
What is the difference between magnesium bisglycinate and magnesium glycinate?
Magnesium bisglycinate and magnesium glycinate are two names for the same supplement. Whether it is absorbed better than magnesium citrate is not yet clear: the studies in healthy people contradict each other, and citrate currently has the strongest evidence base.