Calcium is needed for developing the bones and maintaining their rigidity. It also contributes in forming intracellular cement and the cell membranes and in regulating nervous excitability and muscular contraction. About 90 percent of calcium is stored in bone, where it can be reabsorbed by blood and tissue. Milk and milk products are the chief source of calcium. Calcium builds strong bones and teeth. It also helps prevent Osteoporosis.

Ages 1-10 need 800 mg calcium per day
Ages 11-24 need 1,200 mg calcium per day

To absorb calcium, you should get about 400 IU a day of vitamin D. You can get it in four glasses of milk, most multivitamins, or exposure to the sun. In the South or Southwest, the winter sun is too weak to let your skin make enough vitamin D.

Phosphorus, also present in many foods and especially in milk, combines with calcium in the bones and teeth. It plays an important role in energy metabolism of the cells, affecting carbohydrates, lipids, and proteins.

Magnesium, which is present in most foods, is essential for human metabolism and is important for maintaining the electrical potential in nerve and muscle cells. A deficiency in magnesium among malnourished persons, especially alcoholics, leads to tremors and convulsions.

Sodium, which is present in small and usually sufficient quantities in most natural foods, is found in liberal amounts in salted prepared and cooked foods. It is present in extracellular fluid, which it plays a role in regulating. Too much sodium causes edema, an overaccumulation of extracellular fluid. Evidence now exists that excess dietary salt largely contributes to high blood pressure.

Iron is needed to form hemoglobin, which is the pigment in red blood cells responsible for transporting oxygen, but the mineral is not readily absorbed by the digestive system. It exists in sufficient amounts in men, but women of menstrual age, who need nearly twice as much iron because of blood loss, often have deficiencies and must take in absorbable iron. A good source for Iron is found in beef and cereals.

Iodine is needed to synthesize hormones of the thyroid gland. A deficiency leads to goiter, a swelling of this gland in the lower neck. Low iodine intakes during pregnancy may result in the birth of cretinous or mentally retarded infants.

Trace elements appear in sufficient amounts in most foods. Among the more important trace elements is copper, which is present in many enzymes and in copper-containing proteins found in the blood, brain, and liver. Copper deficiency is associated with the failure to use iron in the formation of lemoglobin.

Zinc is also important in forming enzymes. Deficiency in zinc is believed to impair growth and, in severe cases, to cause dwarfism. Fluor ine, which is retained especially in the teeth and bones, has been found necessary for growth in animals.

Fluorides, a category of fluorine compounds, are important for protecting against demineralization of bone. The fluoridation of water supplies has proved an effective measure against tooth decay, reducing it by as much as 40 percent. Other trace elements include chromium, molybdenum, and selenium.