Most phosphorus is present in the skeleton and teeth as calcium phosphate crystals. The remaining phosphorus exists in a metabolically active pool in body cells and in the extracellular fluid compartment. The mineral is present as part of phospholipids in cell membranes.
Because phosphorus is widespread in food, including processed foods and soft drinks, dietary inadequacy is uncommon. Deficiency tends to only occur in people who are taking phosphate-binding drugs or among older adults due to general poor food intakes.
Most magnesium is found in bone followed by muscle, and the remainder is in soft tissues and body fluids. Magnesium is a cofactor for more than 300 enzymes involved in many aspects of cellular metabolism including fatty acid and protein synthesis and phosphorylation of glucose.
Moderate depletion is prevalent in older populations in Western nations . A high-quality diet will supply adequate magnesium, but as most people do not eat such a diet, the intake tends to be below the RDA for much of the population. Deficiency may be secondary to poor dietary intakes or conditions such as an increased loss of electrolytes or a shift in electrolyte balance, especially decreases in potassium. Magnesium intakes well below the RDA may be related to insulin resistance, metabolic syndrome, high blood pressure, and heart failure [2, 3]. Leukocyte magnesium is the most reliable indicator of the status of the mineral. The tolerable upper intake level (UL) is based only on supplemental and pharmacologic sources. Those with renal insufficiency should avoid large doses of supplemental magnesium as it can have adverse effects on the central nervous system.