The scientific basis of recommended dietary allowances for calcium.

Dietary calcium is required for bone development during growth (attainment of peak bone mass), for maintenance of skeletal integrity during adult life, and thus for prevention of osteoporosis. The Recommended Dietary Allowance (RDA) of a nutrient for a particular group is considered to cover the needs of 98% of all individuals of that group, and thus takes into account a margin of safety to allow for interindividual variation in minimum requirements. It appears to be possible, on the basis of the available scientific literature, to calculate the daily amount of calcium that must be absorbed from the diet to compensate for the endogenous calcium losses (through urine, faeces and skin) and the calcium retention in bone. Similarly, it seems to be possible to obtain a reasonable estimate of calcium absorption for the different groups of the population. From these data, and taking into account a margin of safety, figures are obtained for calcium intake that are in reasonably close agreement with the authoritative 1989 RDAs of the USA Food and Nutrition Board, with the exception of the USA allowance for girls aged 19-25 years (probably too high) and older adults (possibly too low). With regard to optimal calcium intake, some important questions still remain unanswered. These bear upon the issue of calcium intake and peak bone mass development, and upon the effects of non-nutritional factors (e.g. genetics and physical activity) and nutritional factors (e.g. sodium, protein, alcohol and caffeine) on calcium requirements. Furthermore, it would appear that bone development and maintenance of bone health may not be the sole criteria for setting RDAs in the near future. These issues are briefly discussed.