Active Absorbable Algal Calcium (AAA Ca) is made by submaximally (800 degrees ) heating cleaned oyster shell under reduced pressure and mixing it with similarly heated seaweed (Cystophyllum fusiforme). AAA Ca, the best absorbed from the intestine than other available calcium compounds, consequently most efficiently suppresses parathyroid hormone secretion, increases bone mineral density and decreases vertebral fracture. Aging is associated with calcium deficiency, mostly because of the decreased biosynthesis of 1,25 (OH)2 vitamin D in the kidney. Parathyroid hormone consequently increases, contributing to various diseases associated with aging such as osteoporosis or decrease of calcium in the bone, as well as hypertension, arteriosclerosis, Alzheimer's disease and osteoarthritis due to paradoxical increase of calcium in vascular walls, brain, cartilage and intracellular compartment of many kinds of cells. Mild calcium deficiency is hard to detect despite these serious consequences because of the remarkable constancy of blood calcium concentration maintained by elaborate homeostatic control. Only by successfully counteracting calcium deficiency by AAA Ca with outstanding absorbability, the phenomenon of calcium paradox becomes a recognizable reality within our reach.