I've briefly read DR. Carolyn Dean, MD ND's book at Border's once (took about 20min); it's short and easy-peasy. We apparently deplete out Mag a VARIETY of ways:
--breathing --moving --living --generating ATP those little packets of energy produced by mitochondria in every cell (even sperm) -- remember the Ca-Mg-ATPase enzmes from bio? --high cortisol, chronically elevated cortisol (eg, insomnia, stress, physical/mental stress, injections for joints or orally for tx of autoimmune d/o or allergic reactions, etc) --chronic pain syndromes (see above) --autoimmune diseases (Grave's, Hashimoto's, RA, psoriasis, T1DM, etc) --high elevated blood glucoses (due to high urination) --sweating --exercise (esp endurance types) --alcohol --caffeine --diuretics: HCTZ, furosemide/LASIX, bumetanide, metolazone, chlorthalidone, etc --diarrhea --growth (pregnancy, lactation, weight gain, etc) --acute syndromes (preeclampsia, V-tach, DKA, acidosis, etc) --high phytic acid and high whole grain intake (binds iron, minerals including Magnesium) --consumption of nuts/seeds/fruits/veggies grown on depleted soils --consumption of livestock and fowl raised on grain/depleted-soils
Also, with high calcium supplementation (eg, pregnant/lactating women, post-menopausal women, osteopenic/-porotic individuals, food/beverages 'calcium-supplemented'), the minerals Ca++ and Mg++ compete for the same carriers for uptake from the stomach and intestines which prevents uptake of magnesium.
When I initiate vitamin D therapy, I always check the Mag -- baseline and 1-2mos out -- and unless someone is supplementing Mag, the blood levels drop (and I would assume the more accurate assessment, the RBC Magnesium, does critically decrease as well).
Initially with vitamin D therapy, Mag will appear 'high' or normal. This is deceptive. Often PTH is also > 20-30 or elevated abnormally > 65 which indicates bone resorption and breakdown. The serum Mag is being 'sourced' from degradation of the bone matrix until minerals/hormones are re-balanced.
Many conditions are highly associated with low dietary Magnesium: --atrial fibrillation --irregular heart beats (PVCs, PACs) --osteoporosis --muscle spasms/cramping/Charley horses --impaired insulin secretion, insulin resistance --headaches, migraines --hypothyroidism --hyperthyroidism --hypertension --low HDL, high Triglycerides --dysmenorrhea, PMS, peri-menopausal symptoms --impaired clotting
Magnesium (like thyroid hormone) is required by every cell and tissue for every second of our lives to produce ATP and the function of a variety of other vital celllular processes (according to Dr. Dean ~375 but I bet there are more than this now). Maintaining the high end of 'normal' serum levels for Magnesium (2.3-2.6 mg/dl) is extremely prudent if you lack access to RBC Mag measurements. Go by symptoms too -- take enough to eliminate muscle cramps/Charley horses, migraines/headaches, and other overt signs, etc.
Several Magnesium-dependent enzymes exert control on inflammation: -- Mg-ATP complex controls HMG-CoA Reductase, the rate limiting step in cholesterol formation. The authors report "When cellular Mg is low, this ratio tilts towards the active form, and when such a state occurs, more cholesterol, more mevalonate and more of the pathway’s other intermediates will be produced." -- Lecithin cholesterol acyl transferase (LCAT) which lowers LDL and triglyceride levels and raises HDL-cholesterol levels -- Desaturase and other vital enzymes involved in lipid metabolism and balance. "Desaturase catalyzes the first step in the conversion of essential fatty acids (omega-3 and omega-6s) into prostaglandins, which, like the prenylated proteins, have a cascade of stimulating and inhibiting cellular effects important in cardiovascular and overall health."