MENOPAUSE AND OSTEOPOROSIS

As a result of ovarian failure and higher-than-normal excretion of bone calcium in the urine, collagen and mineral levels fall and bone mass is reduced: this condition is known as osteoporosis. The normal ageing process produces Type II osteoporosis, whereas Type I results from premature ovarian failure. Type II is seen in both men and women over the age of 60 and is probably more directly responsible for fractures of the femur in older women than Type I. The two types of osteoporosis represent different bone-loss processes, which merge in later life to cause susceptibility to fractures, loss of height and deformity of the spine.

Any condition which causes menstruation to stop (amenorrhoea) will upset ovulation, with consequent reduction in the availability of oestrogen and progesterone. The likelihood of premature osteoporosis developing is increased by the following: Turner's syndrome (a congenital failure of the ovaries to develop); amenorrhoea caused by too much prolactin in the blood; amenorrhoea caused by excessive physical exercise; amenorrhoea caused by anorexia nervosa; and amenorrhoea caused by drugs used in the treatment of endometriosis and polycystic ovarian syndrome.

Each year, about 40 per cent of trabecular bone and 10 per cent of cortical bone are remodelled. Over an average lifetime a woman may lose about 25-35 per cent of her cortical bone (mainly from the arms and legs), and about 40-50 per cent of trabecular bone. Men, who continue to produce the protective male hormone androgen, lose only two-thirds of this amount.

In women, trabecular bone loss starts as early as 35. The loss (mainly from the vertebrae, wrists and lower jaw) is slow at first, but by the time the menopause is reached constitutes 3-5 per cent per year. This rate persists for another 5-10 years, then slows. Cortical bone loss starts about 10 years later, and is equal in both sexes at the age of 45. In women, the rate is 2-3 per cent per year in the 5-10 years after menopause, then slows.

The amount of bone loss varies from person to person. The reasons for this are uncertain, but factors that are known to influence it are premature menopause (natural or surgical) before the age of 45; osteoporosis in a close female relative; high alcohol intake; cigarette smoking; low body mass i.e. small stature and small bones; inadequate calcium intake in youth; no pregnancies; existing disease of the bones; sedentary lifestyle; long-term use of corticosteroid drugs or thyroxine; anorexia nervosa; caffeine; steroids for arthritis, asthma or ulcerative colitis; and some drugs used in the treatment of epilepsy and endometriosis. It is known that Asian and Caucasian women are more prone to bone loss than women of African origin.

The prevalence and cost of bone fracture

Women (of all ages) sustain 50-70 fractures per 1000 per year, a rate 8-10 times higher than that in men. Twenty-five per cent of women will sustain a significant osteoporotic fracture during their lifetime.

Vertebral fractures can cause collapse or wedging of the bones, resulting in a bent back and a 'dowager's hump'. Loss of height occurs, accompanied by either high or low back pain depending upon the site of collapse.

The associated death rate, from pneumonia, blood clots, infection, stroke and so on, can be as high as 50 per cent within the year following a hip fracture. Only 25-50 per cent of women who survive after sustaining this type of fracture ever regain their full pre-fracture level of function.

In England and Wales in excess of 60,000 hip fractures occur annually, costing the taxpayer ?220 million, and this is rising dramatically. About 7 per cent of women and 3 per cent of men sustain a fracture of the forearm, vertebrae or femur by the age of 60, and this rises to 25 per cent and 8 per cent respectively by the 80th birthday.

In the USA 500,000 vertebral fractures and 200,000 hip fractures occur each year. The remainder of the 1.5 million new fractures are of the wrist, shoulder, pelvis and ankle. Fifty per cent of the total are the result of osteoporosis. Fracture treatment costs a staggering US$18 billion overall. As the number of elderly grow both in the USA and the UK, such costs can only rise further.

Predicting osteoporosis and bone fracture

Apart from the predisposing factors listed on page 39, fracture risk can be predicted by identifying those with reduced bone mineral content or bone density. An early fracture before the menopause, or even before 60, is likely to increase the risk of fracture at a related site later in life.

Recently developed screening techniques have made it possible to measure bone density. Such screening is expensive, but could in future help to cut the costs of fracture treatment.

Of the four available methods, dual absorptiometry (DPA) is useful for lumbar spine and hip bone mineral measurement. Accuracy is within 3-6 per cent for the spine, and 3-4 per cent for the hip. Radiation exposure is low.

Quantitative computed tomography (QCT) is less precise, more expensive and requires greater radiation exposure than DPA.

Single photon absorptiometry (SPA) is convenient for measurement of the forearm site. Accuracy is within 4-5 per cent and radiation exposure low. SPA may be cheaper for mass screening, but the result may be misleading with regard to comparative changes in the bones of other areas, such as the spine or hips.

Dual energy X-ray absorptiometry (DEXA) represents the most recent technological advance. The time required to scan the spine is only seven minutes, compared to 20 minutes for DPA, which reduces radiation exposure. Accuracy and precision are excellent, within 0.5-1.2 per cent.

The diagnosis of osteoporosis and prediction of fracture risk by such techniques are the most accurate currently available. The combination of one measurement of bone mass in the forearm along with new biochemical markers of bone formation (for example, Osteocalcin) may be able, in future, reliably to identify at the menopause those women who are at greatest risk of developing osteoporosis in 10-12 years' time.

The cost of screening has to be carefully weighed against the cost of treating the rising number of osteoporosis sufferers, currently estimated at 2,000,000 in the UK. The increasing cost to the nation of osteoporosis followed by fracture and fracture complication would seem to favour the phasing-in of a screening programme, perhaps giving priority in the first instance to those most at risk. Further studies are required before the value of bone density measurements in such a programme can be assessed.

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Womens health