4.1 Introduction

It has been nearly 30 years since the last FAO/WHO recommendations on calcium intake were published in 1974 (1) and nearly 40 years since the experts' meeting in Rome (2), on whose findings these recommendations were based. During this time, a paradigm shift has occurred with respect to the involvement of calcium in the etiology of osteoporosis. The previous reports were written against the background of the Albright paradigm (3), according to which osteomalacia and rickets were due to calcium deficiency, vitamin D deficiency, or both, and osteoporosis was attributed to the failure of new bone formation secondary to negative nitrogen balance, osteoblast insufficiency, or both. The rediscovery of earlier information that calcium deficiency led to the development of osteoporosis (not rickets and osteomalacia) in experimental animals (4) resulted in a re-examination of osteoporosis in humans, notably in postmenopausal women. This re-examination yielded evidence in the late 1960s that menopausal bone loss was not due to a decrease in bone formation but rather to an increase in bone resorption (5–8); this has had a profound effect on our understanding of other forms of osteoporosis and has led to a new paradigm that is still evolving. Although reduced bone formation may aggravate the bone loss process in elderly people (9) and probably plays a major role in corticosteroid osteo-porosis (10)—and possibly in osteoporosis in men (11)—bone resorption is increasingly held responsible for osteoporosis in women and for the bone deficit associated with hip fractures in elderly people of both sexes (12). Because bone resorption is also the mechanism whereby calcium deficiency destroys bone, it is hardly surprising that the role of calcium in the patho-genesis of osteoporosis has received increasing attention and that recommended calcium intakes have risen steadily in the past 35 years from the nadir which followed the publication of the report from the Rome meeting in 1962 (13). The process has been accelerated by the growing realization that insensible losses of calcium (e.g. via skin, hair, nails) need to be taken into account in the calculation of calcium requirements.