Among all the essential minerals and vitamins you can take in supplement form, magnesium is one of the few that actually has a noticeable effect. That’s probably due to the fact that most people do not get adequate amounts of this mineral from their everyday diet. 
If you search any nutrition store for magnesium supplements, you’ll notice that there are numerous different formulations. Magnesium does not come in its pure elemental form, but rather as a salt or chelate compound that consists of magnesium attached to one or more other molecules — examples: magnesium citrate, magnesium oxide, magnesium taurate, etc.
Different forms of magnesium salts and chelates vary in their bioavailability (absorption rate), efficacy, benefits and side effects.
When broken down by the body, each magnesium salt/chelate initially yields two parts: magnesium and whatever molecule(s) it is attached to. For example, magnesium citrate provides both magnesium and citric acid (citrate), each of which has its own effects within the body.
So now that you see how different forms of magnesium may have different benefits and uses, let us just focus on one of the most popular types of magnesium, and that is magnesium glycinate.
Why Magnesium Glycinate?
Magnesium glycinate is an amino acid chelate of magnesium, which consists of one magnesium ion attached to two glycine ions. Glycine is a non-essential amino acid that has some functions in the human body.
By mass, the compound contains about 14% elemental magnesium, so 100 mg of magnesium glycinate yields about 14 mg of pure elemental magnesium upon digestion.
Magnesium glycinate has higher bioavailability than other kinds of magnesium compounds, i.e. it is better absorbed by the body and thus it is a relatively more effective form of oral magnesium supplements. 
Another advantage of magnesium glycinate is that it is less likely to cause diarrhea. When poorly absorbed, a large percentage of ingested magnesium remains in the intestines and ends up in the colon, where it has a laxative effect.
If you have suffered from diarrhea with other magnesium supplements, this may be the right choice for you. More intestinal absorption = less diarrhea.
Magnesium Glycinate vs. Bisglycinate
You may have noticed that some product labels say magnesium glycinate and others call it magnesium bisglycinate or diglycinate — well, these are just the same compound.
Magnesium bisglycinate is the scientifically accurate name; the compound contains two glycine molecules, hence the prefix “di” or “bis”. For simplicity’s sake, it is often referred to as magnesium glycinate.
A Sleep-Promoting Magnesium
When taking magnesium glycinate you reap the health benefits of both magnesium and glycine.
As far as sleep issues are concerned, magnesium supplementation has been shown to help improve sleep quality, especially for insomniac people and those who don’t get adequate amounts of this mineral from their diet. 
Glycine also has a positive effect on sleep.  Studies found that it improves sleep quality in people suffering from insomnia.  Additionally, it has also been found to improve daytime performance and reduce fatigue in sleep-deprived individuals. 
For these reasons, this is arguably the best and most beneficial form of magnesium to take before bedtime, particularly for people who have difficulty falling or staying asleep.