Osteoporosis is not an inevitable part of ageing. It is the result of significant bone loss over time. The gaps in the bone structure become markedly larger, resembling a honeycomb.
'Porous bones' is the literal meaning of osteoporosis. It results in a weakening of the bone, making it more prone to fractures.
When the amount of bone falls below a critical level (known as the fracture threshold), the skeleton become more liable to easy fracture. Initially osteopenia occurs, when the mciroarchitecture of bone tissue deteriorates. This can advance to osteoporosis.
When bone loss becomes osteoporosis
Osteoporosis was not precisely defined as a disease until 1994. The World Health Organisation (WHO) set criteria for its diagnosis, stating that the disease is present if the bone mineral density is significantly less than the mean of young adults of the same sex.
Types of osteoporosis: Type I (postmenopausal) This is the main category that will be discussed, as it typically occurs between the ages of 50 and 75 years. It is more common in women than men as the main cause is the deficiency of oestrogen. Fractures tend to occur in the more active trabecular bone, especially in the spinal vertebrae (crush fracture) and distal radius (Colles' fracture). Bone loss is accelerated and the absorption of calcium is reduced. Type II (senile) Affects men and women over the age of 70 years, when fractures of both trabecular and corticol bone occur, predominantly in the hip and spinal vertebrae as a wedge fracture. Bone loss is not accelerated in type II osteoporosis, and it is apparent that the raised level of parathyroid hormone is partly responsible. |
Bone loss through the decades
Bone mass naturally decreases. As we get older, the resorption process starts to outstrip bone formation, and they become more porous and weaker. Part of the protein matrix is lost, in addition to the mineral calcium, which results in the loss of bone strength. In addition, the absorption by the gut of the essential nutrients calcium and vitamin D reduces with age.
Our 20s and 30s
The vast majority of bone density or strength is formed by our mid 20s. The balance between bone formation and loss remains stable up to approximately 35 years old, when the majority of people have achieved their peak bone mass. At this stage in life, the rate at which new bone cells replace old ones begins to slow down.
Thereafter, the breakdown of bone outstrips the rebuilding process and bone loss occurs at the rate of 1% a year, as the turnover activity slows with advancing years.
Our 40s and 50s
By the time we reach 50 years old, more bone cells die than are replaced, and the cycle swings towards greater bone resorption. The result is the decrease in bone mass. Bone becomes more porous and weaker and more likely to break and by the age of 70, one-third of the bone density can be lost.
Over an average lifetime, women may lose 25-35% bone in arms and legs and 40-50% in other bone. The initial reduction is slow at first and is mainly from the vertebrae, wrist and lower jaw. The deterioration then increases, reaching losses of 3-5% by the menopause, and then accelerates once more 5 years after the menopause.
Men lose less bone overall, in the region of 25-30%, as they are protected by male hormones (androgens), which are secreted by the testes and help build up protein tissue. Men are not subject to the same degree of hormonal changes as women.
Although bone loss is a natural part of ageing, the development of osteoporosis can be controlled, prevented and treated, to avoid the occurrence of osteoporotic fractures.
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20/05/2009