Introduction
Osteoporosis is a skeletal disorder characterized by weakness and fragility of bones with an increased risk of fractures. Figures from the National institutes of health put the number of Americans with osteoporosis at 10 million, with 1.5 million fractures a year attributed to osteoporosis and the overall health costs at about 14 billion dollars a year. It can occur at any age, but the prevalence increases with age. Women are also more likely to develop the disease than men. A 2004 report by the Surgeon General's office detailed the full extent of osteoporosis and bone health as a public health concern.
How Osteoporosis Develops
Human bone is formed by the action of specialized cells called osteoblasts. These cells continually lay down fibrous bands that provide binding sites for complex calcium compounds. These form a system of rods and plates that make up the structure of bone. Another set of specialized cells, called osteoclasts, continually remove older deposits, encouraging newer bone formation and maximizing the strength of the bone. Thus, human bone is continually developing. Formation of new bone goes on at the same time with breakdown of old bone. The control of this process is complex, involving several hormones, state of physical activity and nutrition.
In the younger age groups, under the control of growth hormone and later on, sex hormones, new bone is laid down faster than it is broken down, leading to overall increase in size and density of bones in the body. After the age of 20 years, there is generally a balance between old bone break down and new bone formation. After the age of 50 years or with the onset of menopause in women, old bone breakdown, also known as resorption, overtakes new bone formation with a tendency towards decreased bone density.
The drop in sex hormone activity with age also leads to reduced vitamin D and calcium absorption in the intestines with an increase in excretion of calcium in the kidneys. The net loss of calcium leads to the release of the parathyroid hormone, which encourages the release of calcium from bony stores by the breakdown of bone.
Decreased bone density weakens the bones, making them more porous and unfit for the weight bearing and postural functions they were meant for. In serious cases, actual size reductions with postural changes can occur. More frequently, pathological fractures usually in the wrists, hips or spine announce the presence of osteoporosis.
Types of Osteoporosis
The report from the Surgeon General detailed two types of osteoporosis: primary and secondary. Primary osteoporosis is usually age related and results from the normal reduction of activity of the bone forming osteoblasts or the reduction of the enhancing effects of the waning sex hormones with age. Calcium and vitamin D deficient diet, genetic predisposition and a lifestyle of reduced physical activity and smoking all enhance the development of this type of osteoporosis.
Secondary osteoporosis is seen in certain conditions that promote resorption of bone or actively stop new bone formation. Endocrine diseases with hormonal imbalances, drugs like steroids and antiepileptics, genetic diseases like cystic fibrosis, paralytic illnesses, gastro-intestinal diseases and surgical resection involving the intestines and alcoholism are among the conditions that lead to secondary osteoporosis.
