Effect of calcium on skeletal development, bone loss, and risk of fractures

Abstract

In assessing the role of calcium, it must be stressed that calcium is not the cause of bone health but simply a necessary condition for it. It is mechanical usage that is of primary importance for bone. In just the same way iron is essential for hemoglobin synthesis and protein is essential for muscle mass, but neither is sufficient by itself. What, then, ought we to expect from a high calcium intake? Can we prevent estrogen-withdrawal bone loss? No. Calcium is not a substitute for estrogen, anymore than it is a substitute for exercise. Will calcium slow the remodeling loss that occurs with aging? Yes, to some extent; as calcium slows remodeling, it will inevitably slow remodeling-related loss. But most importantly, a high calcium intake will prevent calcium-deficiency bone loss. The only question, therefore, is the extent to which calcium deficiency loss may contribute significantly to bone fragility in various populations. The bone loss and fracture data reviewed briefly here indicate that an important portion of the osteoporotic fracture burden is calcium-related. What that portion is will be a function of the fraction of the population with inadequate intakes in any given country. Better than half of all adult American women have calcium intakes <500 mg/day, whereas only a small fraction of Dutch or Danish women, for example, would be under that level. Hence, a population-wide program to increase calcium intake in the United States would be likely to yield a greater benefit than in either the Netherlands or Denmark. That does not mean, of course, that there could not be substantial benefit to individuals with low intakes in all countries. Calcium intakes of ≥1,500 mg are both safe and natural. While not all bone loss and low trauma fractures are due to low calcium intake, some almost certainly are. Adaptation to low intakes does occur, but it is seldom sufficient to compensate for the low intake. We cannot easily distinguish those who need more calcium from those who need less, and for that reason it makes good sense to ensure an adequate calcium intake for the entire adult population. What should that intake be? During adolescence, 1,500 mg will come close to ensuring the achievement of genetically programmed levels of peak bone mass. And for adults, the intakes endorsed by the 1984 Consensus Conference [38] still appear to be the best estimates: 1,000 mg/day for estrogen-replete women and 1,500 mg/day for estrogen-deprived women.