Osteoporosis, the degeneration of the bone structure through a progressive reduction in bone mass and bone density, is one of the leading bone diseases, whose prevalence in most countries of the industrialized world has increased dramatically over the past 20 years. In the United States alone, it is estimated that 1.5 million fractures per year are directly attributable to osteoporosis. Osteoporosis is a skeletal condition that is tied almost exclusively to the life style, dietary, and exercise habits of its subjects. Osteoporosis most frequently affects the hip, spine, and wrist, making the bones fragile and less able to absorb a shock or a blow. The progress of osteoporosis is not forecast by the development of specific symptoms; it is painless, first manifesting itself with a fracture, often in the course of a fall or other accident.

An understanding of the causes of osteoporosis begins with the formation and the growth of bones. Bones begin their development in the body at birth, and continue until full maturation at the approximate age of 20. The mineral calcium is the most important element in the formation of the cells that are used in bone construction. Calcium is found in many food products, particularly milk and other dairy products. Calcium requires the presence of vitamin D in the body to be properly absorbed into the various systems where it plays a role in human function; even when a person is otherwise consuming appropriate amounts of dietary calcium, a vitamin D deficiency will contribute to a calcium deficiency. There is no substitute within the human biology for calcium in bone construction, and when the bone does not receive the proper amount of this mineral, the bone cannot be either as dense or as hard as it must be to function properly.

Collagen is another component of bone formation. Collagen is the protein-based substance that gives the otherwise inflexible bone some measure of elasticity on impact. Although far less important to lifelong bone health, a deficiency in this protein during the adolescent period will contribute to the potential for bone disease later in life. The mineral potassium is also an essential but less substantial part of the bone development process.

The healthy formation of bones during the period prior to physical maturity also requires a healthy and active lifestyle. Exercises and sports that require the bone to bear resistance, such as running, jumping, cycling or any other movement where forces are directed into the bone structure, assist in the development of both bone mass and density. Later in life, bone mineral density is the indicator relied on by the medical community in assessing the health of older bones. There is considerable sports science evidence that confirms that young people who participate in sports or other regular and structured physical activities are far more likely to have healthy bones in their later adult years.

While the foundation of healthy bones is established as a young person approaches physical maturity, the issue of lifestyle continues to be operative in bone health through adulthood. Participation in activities that provide resistance continues to assist the body in the maintenance of bone density. While it is an unalterable genetic fact that adult bone mass will begin to decrease after age 40 in most persons, the rate of this decrease is significantly slowed by the combined attention to diet and exercise.

Post-menopausal women are the largest single group of persons afflicted by osteoporosis, which generally is most often diagnosed in persons who are over the age of 50 years. Menopause tends to cause a reduction in levels of estrogen, the female hormone. As many women breastfed one or more children, there exists a potential limitation on the amount of calcium that such women received into their own bodies during such periods. For other affected persons, the most common factors identified

Illustration showing a hip fracture due to osteoporosis.
as contributing to osteoporosis include a bone fracture of any type that occurs after age 50, insufficient intake of calcium and vitamin D, low testosterone levels in males, sedentary lifestyle, excessive alcohol consumption, smoking, and the use of corticosteroid medications, such as cortisone, for extended periods.

Osteoporosis is an almost entirely preventable disease. It is also an incurable and progressive condition, as once bone mass is decreased, it cannot be increased, but simply maintained. If aggressive steps are not taken to address the identified causes of the condition, the bone mass will continue to deteriorate, with the bones being prone to fracture more readily. The approaches to healthy bone development over a lifetime are the same techniques to be employed in countering the effects of osteoporosis. These approaches include a balanced diet (with emphasis on calcium and vitamin D consumption), weight-bearing, resistance exercises that require the bones to respond to force, and abstinence from smoking. In some circumstances, a physician may prescribe supplements to assist with the maintenance of proper calcium levels in the body.

SEE ALSO Bone, ligaments, tendons; Calcium; Osteoarthritis.