Postmenopausal Osteoporosis
There are four main types of osteoporosis: juvenille, idiopathic, postmenopausal and senile. This entry deals with the cause and prevention of postmenopausal only.
Postmenopausal Osteoporosis is a condition that mainly affects older women and is characterized by a decrease in bone mass.

The Cause
There are two main types of cells in bones, called osteoclasts and osteoblasts, and these destroy and rebuild the bones in microscopic quantities. The osteoclasts dissolve cavities in the bones, and the oesteoblasts repair the cavity, filling it with new bone. In postmenopausal osteoporosis, more osteoclasts than usual are working, each creating a bigger cavity than before. The osteoblasts still appear for repairs, but this is no longer sufficient to completely fill the cavities. As the bone mass falls, the bones become honeycombed inside, and are much more likely to break after a fall.
If there is not enough calcium in the blood it is withdrawn from the bones, only being replaced when the level in the blood is stable. Any excess is treated as waste. The more calcium is withdrawn from the bones, the weaker they become. The weaker they become, the less space there is to store calcium. A vicious circle has begun.
In women, the hormone oestrogen also contributes to bone growth. During the menopause, the amount produced begins to fall until eventually almost none is produced as the menopause ends1. Other factors can affect the speed of bone loss, but the loss of oestrogen is the main cause.

Prevention
The best women can do for their bones to protect them from the loss of oestrogen is to make sure that they reach peak bone mass, thus giving them the strongest chance to survive.
For under 25s
Take plenty of exercise and the equivalent of half a litre of milk a day.
Eat a balanced diet, including protein, fresh fruit and vegetables, dairy products and roughage.
Go out in the sunlight with bare arms and legs as much as possible. Twenty minutes per day gains the appropriate amount of vitamin D in the summer.
Don't smoke and drink as little alcohol as you can.