Magnesium Digestion and Absorption
Ingested magnesium is absorbed in the intestines and then transported by the blood to the cells and tissues. Most of the non-absorbed magnesium is passed as urine, and in individuals whose kidneys are functioning normally, the process is remarkably efficient. Neither too little nor too much magnesium is excreted in this manner, so blood levels remain stable. Additional magnesium is lost in feces (normally about 25-50 mg/day) and sweat (normally about 15 mg/day).
Usually, in healthy individuals, about 40-50% of consumed magnesium is absorbed. However, absorption rates can vary from as little as 25% to as much as 75%, depending on such factors as stomach acid level, body needs, and type of diet. Certain medical conditions such as liver disease, colitis, and diabetes can adversely affect absorption, as can physical or psychological stress or the use of diuretics or birth control pills.
Doctors frequently recommend taking magnesium supplements as either a preventative or therapeutic measure in at-risk patients. The magnesium included in dietary supplements can either be in chelated form (connected to an amino or organic acid) or non-chelated (as in magnesium oxide, sulfate or carbonate). The chelated forms of magnesium are more easily absorbed.
Absorption is also facilitated in an acidic stomach environment. Therefore, magnesium supplements are best taken between meals or at bedtime, preferably with Vitamin C (ascorbic acid). Furthermore, many calcium/magnesium combinations include both hydrochloric acid and Vitamin D to make both minerals easier to absorb. Fructose and oligosaccharides are other commonly used additives included in supplements to improve magnesium absorption.