Osteoporosis according to the WHO definition, is the "progressive systemic skeletal disease characterised by low bone mass and micro-architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture".
There are 2 components to osteoporosis (1) weak bones, resulting in (2) increased susceptibility to fractures.
Bone strength is dependent on 2 factors: (1) bone density and (2) bone quality.
As there are currently no reliable methods of measuring bone quality, the diagnosis of osteoporosis tends to be made based on bone mineral density (BMD).
NATURAL HISTORY OF BONE LOSS Bone density increases from birth through adolescence, reaching a peak in the twenties.
Genetic, environmental and nutritional factors all play a role in contributing to the peak bone density achieved.
There is then slow, minimal decline in bone density from about 30 to 50 years.
In men above 50 years, bone density declines at a rate of about 0.
2 - 0.
5% per year.
In post-menopausal women, the rate of decline is significantly higher, at about 3-5% per year for about 5 - 8 years, then slows to about 1-2% per year thereafter.
HOW COMMON IS OSTEOPOROSIS? The estimated worldwide prevalence of osteoporosis in women is as follows:

• 50 - 59 years old - 4%.
  
• 60 - 69 years old - 8%
• 70 - 79 years old - 25%
• 80 years and above - 48%

In developed economies such as Singapore, the prevalence of osteoporosis is likely to increase as the population ages.
In 2005, 1 in 12 was over 65 years.
In 2030, 1 in 5 will be above 65 years.
CONSEQUENCES OF OSTEOPOROSIS AND THE RESULTING FRACTURES Falls are more common among the elderly.
A simple fall on weakened bones often result in fractures, and this most commonly occurs to the hip, vertebrae and wrists.
The statistics are grim.
Up to 25% of patients do not survive beyond 1 year after a hip fracture.
Of those who do, 20% become semi or fully dependent, and 40% experience some form of reduced mobility.
RISK FACTORS:

• Advanced age
• Female gender
• Caucasian or Asian race
• Thin and small body frame
• Positive family history of osteoporosis
• Personal history of fractures as an adult
• Excessive alcohol consumption
• Smoking
• Low dietary calcium
• Lack of exercise, in particular, weight-bearing exercise
• Malnutrition and poor general health
• Low estrogen states in women (eg.
  After menopause, removal or damage to ovaries)
• Low testosterone levels in men
• Chronic immobility
• Certain medical conditions eg.
  Hyperthyroidism, hyperparathyroidism, rheumatoid arthritis
• Certain medication eg.
  Heparin, phenytoin, corticosteroids

Clinically, one can estimate the risk of osteoporosis by the Osteoporosis Self-Test for Asians (OSTA) scoring system.
This is calculated as follows: Age (in years) - Weight (in kg) = OSTA Score Interpreting results: OSTA High > 20 Risk of having osteoporosis is high (about 61%) OSTA Moderate 1-20 Risk of having osteoporosis is moderate (about 15%) OSTA Low Test to check Bone Mineral Density The DEXA (dual-energy x-ray absorptiomety" scan is considered the most accurate test for the diagnosis of osteoporosis.
It is translated as a T-score.
The WHO has established the following guidelines.
T score > -1.
0 Normal T score -1.
0 to -2.
5 Low bone mass (osteopenia) T score Lifestyle Changes That Will Help

• Adequate intake of Calcium and Vitamin D
• Exercise - both weight-bearing and resistance training exercises have been shown to be effective in improving bone mineral density in women.
  Exercise also improves physical strength and postural stability, thus reducing risk of falls and further fractures.
  
• Avoid smoking and alcohol consumption - both are associated with increased risk of osteoporotic fractures.
  
• Fall prevention

If your doctor has assessed that you require treatment, you may be started on the following medication.
The choice of drug will depend on efficacy, ease of administration and cost, amongst other factors to be considered.

1. Bisphosphonates
2. Strontium ranelate
3. Raloxifene
4. Calcitonin
5. Teriparatide