Bones for the future.

In the course of the present century the major metabolic bone problem in the West of Scotland and Northern Europe in general has changed from that of rickets/osteomalacia with its attendant deformity and loss of stature, to osteoporosis and a consequent epidemic of fractures in older people. Advances in understanding the intermediary metabolism of vitamin D have resulted in a better appreciation of the role of air pollution in the rickets pandemic during the latter part of the 19th and early part of the 20th century, but the persistence of the problem in Asian immigrants and in certain special clinical situations had led to a reappraisal of the importance of dietary constituents other than vitamin D itself. Technical advances in the measurement of bone mass have permitted a closer examination of the aetiological factors influencing bone mass and fracture incidence. It seems likely that there is a relationship between increased dietary calcium intake in childhood and adolescence and peak bone mass in the fourth decade, but the definition of "adequate" and "optimum" remains insecure. The most important reason for women becoming at risk of fracture in later life relates to the dramatic reduction in bone mass consequent upon the menopause--a feature which can be arrested by the administration of oestrogen but hardly at all by calcium. The bulk of evidence supports the view that the negative calcium balance found in post menopausal osteoporosis is a consequence rather than a cause, and that dietary calcium can only--if at all--influence the course of events if pushed up to unusually--and for many, intolerably--high levels. Although other life style components such as exercise, alcohol consumption or cigarette smoking may also have a role, the principal impact on reducing the problem of post menopausal fracture is likely to be through the wider acceptance of hormone replacement therapy.