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Relative importance of (1) peak bone mass and (2) rates of bone loss in determining fracture risk of older women

Bone Mineral Density (BMD) is a key recognised predictor of fracture risk. This is evidenced by standards specified by the World health Organisation (WHO) in using absolute BMD for the diagnosis of osteoporosis. These standards stipulate that persons with a BMD value more than 2.5 standard deviations below the average specified for a 25-year-old Caucasian female are defined as having osteoporosis, while those between 1.0 and 2.5 standard deviations below the average are considered to have osteopenia (Shoback et el,2001,p.314).

Osteoporosis is a clinical term to imply reduced bone density; a condition associated with high morbidity and mortality. Where the reduction is mainly in the trabecular bone, the commonest complications are crush fractures of vertebrae, which may manifest as reductions in height and "dowager's humps". However, if cortical bone is involved, fractures of long bones such as those involving the neck of femur are likely; this is a major cause of death especially among older women (Longmore et al, 2004,p.698)

Barger-Lux et al (2005) reporting on a randomised controlled trial which looked at the augmentation of bone density following calcium supplementation of 152 post-adolescent healthy young women consuming a diet moderately low in calcium, concluded that the combined impact of increased dietary intake of calcium and the small quantity of calcium provided in the form of multivitamin tablets together, resulted in a mean increase in the control group (800 mg or 20 mmols per day) which was "possibly at or near the threshold beyond which additional calcium has no further effect on bone accrual" (Barger-Lux et al,2005). Woo et al (2007) reporting on a 2 year study involving 441 women between the ages of 20 and 35, looking at milk supplementation and bone health, also concluded that milk supplementation was not associated with consistent changes in BMD in that age group.

It seems reasonable therefore to conclude that the current scientific evidence does not support mandatory calcium supplementation of all young women, as means of reducing the longer term risk of osteoporosis. However, this should not be taken to mean that young women exposed to particularly lower levels of dietary calcium would not benefit from calcium supplementation, as indicated in the BNF quoted above.

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