ATP used in the body is always Mg-ATP 5. Most Americans are deficient. They were not meeting the older, lower recommendations. Deficiencies might be caused by inadequate intake, alcohol consumption, diarrhea, diuretics, and sweating. Symptom of toxicity is diarrhea.
Absorption takes place in the small intestine.
There are only about 20 to 28 grams of magnesium in the human body. About a fourth is in the muscle and red blood cells. Excretion is through the urine, feces, and sweat. Alcohol cause magnesium to be rapidly washed out of the body. When a law enforcement agent stops a driver on the suspicion of driving under the influence, he may check to see if the driver's eyes can smoothly follow a moving object.