If you are lactose intolerant you will need to plan carefully, eating lots of yogurt and real cheese and perhaps even taking supplements. Serum levels are controlled by Vitamin D and the parathyroid horme. Absorption is facilitated by an acidic environment in the small intestine, the presence of glucose and lactose in the intestinal tract and by normal intestinal motility. Absorption is depressed by excessive protein, caffeine, tannin in tea, phytates in grains, oxalates in green vegetables, smoking, alcohol intake, menopause, diarrhea, some medications, and old age. Storage is in the bones and teeth and can be drawn upon in times of need.
Excretion is through the kidneys if the blood levels are too high.
If the body does not need calcium from food it remains in the small intestine, combines with fat, and is excreted from the bowel as a soap. The muscle cell cannot contract again with out relaxing. Magnesium is necessary for the muscle cell to relax. Therefore, both are needed each time a muscle is used. As calcium causes the smooth muscles in the blood vessels to contract, the heart pumps harder and causes a reflexive lowering of blood pressure.