The bones. Osteoporosis is thinning of the bones, and happens in men and women with ageing, but it is women who have the most significant and clinically important bone loss. Women’s bones never build up the same maximal bone density as men, who have thicker and stronger bones. (This peak bone density is usually reached during your twenties.) So women start off with relatively less bone density than men, and after menopause women have an accelerated rate of bone thinning, due to the drop in the level of circulating oestrogen.
These factors result in post-menopausal women having five times the rate of bone fracture of men of the same age. By the age of 70, 10 to 15 per cent of women will have suffered a break in a limb or a crush-type break in a vertebral (spinal) bone. (By the age of 80, about one-third of women will have had a fracture.) Many of these women will require hospitalisation. That means a great deal of suffering and expense is incurred when the bones get brittle.
Measuring bone density by a specialized testing method (bone densitometry), is becoming more widely practiced, and is being used in research. It would seem that not all women have the same risk of developing osteoporosis. Important factors include a family history, weight and smoking. At higher risk would be a fairly inactive, thin, smoking woman, whose diet is low in calcium, who doesn’t see much sunlight, and whose mother had several broken bones in her later years.
Osteoporosis is a relatively slow, silent process. It is not as though with your final period you develop a hunched back. It can take years for the changes to show as broken bones, or lost height, or a marked stoop, but the process begins around menopause in most women who are susceptible to it.
One factor which determines how thin your bones get is how thick they were to begin with (that is, the peak bone density). Maximising your peak bone density in your teens and twenties, by having adequate calcium in your diet, and getting plenty of weight-bearing exercise (like walking), can decrease your chances of problems later in life. It is like making deposits in your ‘bone bank’ for later on.
If you have bone thinning during these earlier years, when you are meant to be building up your peak bone density, you may be increasing your risks of osteoporotic fractures later in life. Bone thinning may occur if there is a prolonged time of decreased oestrogen production, for example in conditions like anorexia nervosa. Over time, weight-related and exercise-related amenorrhoea (no menstrual periods) can sap away your bone density, similar to post-menopausal bone thinning. So doctors would recommend giving oestrogen, usually in the form of the oral contraceptive pill, to women who have lengthy spells (over six to eight months) of amenorrhoea.