Boning up on osteoporosis - includes list of information sources and related articles on calcium intake and risk factors for osteoporosis

FDA Consumer, Sept, 1996 by Carolyn J. Strange

Consider an insidious condition that drains away bone--the hardest, most durable substance in the body. It happens slowly, over years, so that often neither doctor nor patient is aware of weakening bones until one snaps unexpectedly. Unfortunately, this isn't science fiction. It's why osteoporosis is called the silent thief.

And it steals more than bone. It's the primary cause of hip fracture, which can lead to permanent disability, loss of independence, and sometimes even death. Collapsing spinal vertebrae can produce stooped posture and a "dowager's hump." Lives collapse too. The chronic pain and anxiety that accompany a frail frame make people curtail meaningful activities, because the simplest things can cause broken bones: Stepping off a curb. A sneeze. Bending to pick up something. A hug. "Don't touch Mom, she might break" is the sad joke in many families.

Osteoporosis leads to 1.5 million fractures, or breaks, per year, mostly in the hip, spine and wrist, and costs $10 billion annually, according to the National Osteoporosis Foundation. It threatens 25 million Americans, mostly older women, but older men get it too. One in three women past 50 will suffer a vertebral fracture, according to the foundation. These numbers are predicted to rise as the population ages.

Osteoporosis, which means "porous bones," is a condition of excessive skeletal fragility resulting in bones that break easily. A combination of genetic, dietary, hormonal, age-related, and lifestyle factors all contribute to this condition.

Changing attitudes and improving technology are brightening the outlook for people with osteoporosis. Nowadays, many women live 30 years or more--perhaps a quarter to a third of their lives--after menopause. Improving the quality of those years has become an important health-care goal. Although some bone loss is expected as people age, osteoporosis is no longer viewed as an inevitable consequence of aging. Diagnosis and treatment need no longer wait until bones break.

There is no cure for osteoporosis, and it can't be prevented outright, but the onset can be delayed, and the severity diminished. Most important, early intervention can prevent devastating fractures. The Food and Drug Administration has revised labeling on foods and supplements to provide valuable information about the level of nutrients that help build and maintain strong bones. FDA has also approved a wide variety of products to help diagnose and treat osteoporosis, including several just last year.

Bone Life

Bone consists of a matrix of fibers of the tough protein collagen, hardened with calcium, phosphorus and other minerals. Two types of architecture give bones strength. Surrounding every bone is a tough, dense rind of cortical bone. Inside is spongy-looking trabecular bone. Its interconnecting structure provides much of the strength of healthy bone, but is especially vulnerable to osteoporosis.

"We tend to think of the skeleton as an inert erector set that holds us up and doesn't do much else. That's not true," says Karl. L. Insogna, M.D., director of the Bone Center at Yale School of Medicine, New Haven, Conn. Every bit as dynamic as other tissues, bone responds to the pull of muscles and gravity, repairs itself, and constantly renews itself.

Besides protecting internal organs and allowing us to move about, bone is also involved in the body's handling of minerals. Of the 2 to 4 pounds of calcium in the body, nearly 99 percent is in the teeth and skeleton. The remainder plays a critical role in blood clotting, nerve transmission, muscle contraction (including heartbeat), and other functions. The body keeps the blood level of calcium within a narrow range. When

A complex interplay of many hormones balances the activity of the two types of cells--osteoclasts and osteoblasts--responsible for the continuous turnover process called remodeling. Osteoclasts break down bone, and osteoblasts build it. In youth, bone building prevails. Bone mass peaks by about age 30, then bone breakdown outpaces formation, and density declines.

The skeleton is like a retirement account, but in our skeletal "account" we can deposit bone only during our first three decades. After that, all we can do is try to postpone and minimize the steady withdrawals. Osteoporosis is the bankruptcy that occurs when too little bone is formed during youth, or too much is lost later, or both.

"You've got to get as much bone as you can and not lose it," Insogna says. "The most important risk factor for osteoporosis is a low bone mass."

"The upper limit of bone mass that you can acquire is genetically determined," says Mona S. Calvo, Ph.D., in FDA's Office of Special Nutritionals. "But even though you may be programmed for high bone mass, other factors can influence how much bone you end up with," she says. (See "Reducing Your Risk.") For instance, men tend to build greater bone mass, which is partly why more women face osteoporosis.

But there's another reason. With the decline of the female hormone estrogen at menopause, usually around age 50, bone breakdown markedly increases. For several years, women lose bone two to four times faster than they did before menopause. The rate usually slows down again, but some women may continue to lose bone rapidly. By age 65, some women have lost half their skeletal mass. Because the changes at menopause increase a woman's risk, many physicians feel it s a good time to measure a woman s bone density, especially if she has other risk factors for osteoporosis.