While magnesium deficiency is fairly common, it is frequently overlooked as a source of problems. The reason is that serum magnesium levels (the test most doctors use) do not reflect body stores of magnesium. Blood levels are kept within the normal range at the expense of other tissues. Many people do not get enough magnesium from their diet for reasons including the following:

• The amount of magnesium in the soil in which the food is grown may be reduced.
• Magnesium can be lost in the processing and refining of foods and in making oils from the magnesium-rich nuts and seeds. Nearly 85% of the magnesium in grains is lost during the milling of flours.
• Soaking and boiling foods can leach magnesium into the water, so the "pot liquor" from cooking vegetables may be high in magnesium and other minerals.
• Oxalic acid in vegetables such as rhubarb, spinach and chard, and phytic acid in some grains may form insoluble salts with magnesium, causing it to be eliminated rather than absorbed.
• Supplemental vitamin D or calcium reduces magnesium uptake.
• Diets high in phosphorus (meat, milk products, lentils, seeds, beans, nuts, chocolate, peanut butter, bran) reduce magnesium uptake.
• Magnesium elimination is increased in people who use alcohol, caffeine or excess sugar, or who take diuretics or birth control pills.
• Magnesium is absorbed toward the end of the small intestine. If any portion of this area (called the ileum) has been removed, magnesium absorption will be reduced.