Fast and slow bone losers. Relevance to the management of osteoporosis.

A low bone mineral density (BMD) is presently regarded as the most important risk factor for the development of osteoporosis. BMD is a function of peak bone mass attained during growth and subsequent age-related bone loss. BMD can be measured accurately and precisely, although the rate of bone loss is more difficult to assess. When axial BMD was measured, the rate of bone loss was shown to increase by 2- to 4-fold at the menopause. Although this rate varies markedly between individuals, it is symmetrically distributed, which argues against the existence of a subpopulation of fast bone losers. Levels of biochemical markers of bone turnover (e.g. osteocalcin, bone specific alkaline phosphatase, deoxypyridinoline) also increase markedly at the menopause, and individuals with a high turnover tend to lose bone more rapidly. Moreover, since increased bone resorption also results in qualitative changes regardless of BMD, a high bone turnover constitutes an independent risk factor. Currently, large intraindividual variations (10 to 40%) in levels of biochemical markers and assay errors still limit our ability to correctly classify individual patients as fast or slow bone losers. The routine use of these markers as a screening tool to predict the risk of osteoporosis in individuals is of limited value, although their selective use in therapeutic decision-making is more promising.