4. Osteoporosis, low back pain, and other bone disorders.(Disease/Disorder overview)

The human skeleton is an intricate framework of 206 bones that give the body its structure and shape. These bones serve as armor for vital organs and soft tissue, a storehouse for minerals, and a birthplace for blood cells. Together, the bones act in concert with the muscles, ligaments, tendons, and other connective tissue to give humans an amazing range of movement.

Most bone diseases are rare, but a few pose serious health problems. Osteoporosis, the brittle-bone disease, affects more than 10 million Americans, and an additional 19 million have a low hip-bone mass that puts them at increased risk of the disease. Osteoarthritis, the most common form of arthritis, is widespread among people over 40. (See Chapter 3, "Coping with Arthritis.") Low back pain, which often results from slipped vertebrae or disks, is the second most frequent cause of lost work for adults under 45 years of age.

How Bones Are Structured

Bones are made of inorganic salts--including calcium and phosphate--imbedded in collagen fibers. Though solid and seemingly completely formed, bones undergo constant renewal and change. The marrow, or soft center, of certain bones serves as a spawning ground for the many different cells that make up the blood.

There are three types of bones--long, short, and flat or irregular. Long bones include the humerus, radius, and ulna of the arm; the femur, tibia, and fibula of the leg; and the phalanges, metacarpals, and metatarsals of the hand and foot. The tarsal in the foot and the carpal in …