Magnesium is needed for more that 350 different enzymes in the body. Deficiency has been related to many health conditions including osteoporosis, asthma, PMS, hypertension, chronic fatigue syndrome, cardiovascular disease, and diabetes. Muscle spasms/contractions in the calves and soles of the feet are very common and especially indicative of magnesium deficiency.
Magnesium is found in foods such as: list and green vegetables, legumes, seeds and chocolate. In fact chocolate cravings is a common sign that you need more magnesium.
Magnesium deficiency is extremely common. People do not each enough magnesium rich foods such as green leafy vegetables. Disorders of the kidneys or poor digestion can also lead to magnesium deficiency. Stress causes the body to dump magnesium out through the urine. Therefore even if you are eating an ideal diet, you may still be deficient in magnesium.
Standard blood tests:
Blood is made up of the fluid portion (serum) and cells (red blood cells, and white blood cells). Most times doctors test for magnesium they are looking at serum levels. This is in fact a very poor test. Only about 1% of magnesium is stored in blood serum, and this levels is very tightly regulated by the body. In case of magnesium deficiency, levels will fall elsewhere, such as inside the cells (intracellular) long before deficiency shows up in blood serum.
Therefore, it's possible to have a magnesium deficiency, but still have normal blood serum magnesium levels. In fact, only the worst cases of magnesium deficiency will show up in blood serum.
The best way to test magnesium is by a "Red Blood Cell Magnesium." This measures levels of magnesium inside the red blood cells and represents how much magnesium is available to your cells. RBC magnesium is available from standard labs such as Quest or Lab Corp, so all you have to do is ask your doctor to include it on your next lab tests.
Alternatively, specialty lab companies such as Doctors Data or Metametrix offer a Red Blood Cell element test panels. These measure a whole spectrum of intracellular minerals in addition to magnesium. However these tests are generally not covered by insurance, and are only offered by a relatively small number of doctors (mostly who specialize in natural or integrative health). Often naturopathic doctors, chiropractors, integrative doctors or other practitioners in natural health are the best people to go to for this type of advanced functional testing.