There is an epidemic of osteoporosis in the west where 1:3 women and 1:8 men get it. It barely exists in the third world, as diet and exercise play a major role in preventing it. Osteoporosis is caused by the absorption of old bone by osteoclast cells exceeding the deposition of new bone by osteoblast cells. Oestrogen slows down the action of osteoclasts, whereas progesterone stimulates osteoblast activity. Most at risk are those who: excercise excessively, ie. marathon runners and ballet dancers; under excercise; are or were anorexics and bulimics; smoke ; drink excessive alcohol; are deficient in vitamin D, calcium or magnesium; had previously taken/are taking steroids, ie. cortisone and the Pill; had thyroid disease; had a loss of menstruation for greater than 6 months, other than; eat an acid diet of meat, dairy and refined grains with little vegetables, a typical western diet (there is now evidence of osteoporosis being found in teenagers). Most western diets are very high in protein which causes calcium to be lost from the bones, over 2%/year in some people, but low in magnesium which is needed by an enzyme before it can deposit any calcium in the bones. Taking large quantities of calcium without reducing protein intake will not improve bone density. High levels of calcium in the blood has been implicated in gall and kidney stones, calcification of the arteries and brain and arthritic spurs. Without magnesium and vitamin B6 calcium tends to be deposited in the soft tissues. It is generally believed that osteoporosis in women is due to oestrogen loss beginning at menopause as it often starts in women during their mid thirties when they are still making a great deal of oestrogen, this argument doesn’t hold much water. In fact some women have lost 25% of their bone density by the time they reach menopause. Taking oestrogen will slow the loss of bone for up to 5 years, thereafter its benefit declines. Once the oestrogen is stopped the bones are quickly broken down. Progesterone, because of it’s affect on osteoblast cells, is actively involved in the building of bones. But unlike oestrogen, if the treatment is stopped the bones remain strong.