SummaryCalcium is the most abundant mineral in the body and has important structural and metabolic roles. In the average British diet, milk and other dairy products and fortified white bread provide the major supply. The average intake in the UK is well above the current recommended daily amount although the intakes of some school girls are quite low and may be a cause for concern. The amount of calcium which is absorbed and excreted is affected by a number of dietary and physiological factors. The plasma ionized calcium concentration is maintained by the concerted action of 3 hormones, parathyroid hormone, vitamin D and calcitonin. Dietary calcium has been implicated in the development of osteoporosis through failure to achieve an adequate peak base mass during early years or an increased rate of bone loss in later life. The first possibility has not yet been addressed and the second has not yet been resolved. Calcium requirements are difficult to determine confidently and further research on the relationship between calcium and the attainment of peak bone mass in early life and of the ability of individuals to adapt to different calcium intake is needed.