Prevention of osteoporosis: calcium nutrition.

Calcium is a threshold nutrient which means that a nutritional response in terms of calcium balance or bone mass will be present at intakes below the threshold and not above. The analogy can be made with the case of iron nutrition and anemia. Estimates of the threshold intake levels can be made for all stages of life based on available calcium balance data. They range between 1.3 g/day for infants to 1.5 g/day for women past menopause. Calcium nutrition is most important during growth and development in achieving genetically programmed peak skeletal mass. It is also important in maintaining bone mass in the elderly years. Calcium needs are supplied by the breakdown of the skeleton during the first few years after menopause, and thus calcium nutrition is less important until about 5 or 6 years after cessation of menses. Optimum calcium intake is best obtained from food sources; however, the lower food intake of modern humans compared with the food intake of humans during involution has resulted in difficulty in gaining an adequate intake of calcium. Calcium supplements are destined to become and important source of dietary calcium and thus some attention must be paid to their nutritional value. Solubility of a calcium salt is not a major determinant of absorbability over a range of 5 orders of magnitude of solubility. However, there is a well-defined enhancing effect of the co-ingestion of a meal with calcium supplements. It would seem prudent to recommend that any calcium supplement be given at meal times.(ABSTRACT TRUNCATED AT 250 WORDS)