Effect of age on variables relating to calcium and phosphorus metabolism in women

Lack of adequate data concerning the effect of age on biochemical variables relating to bone and mineral metabolism hampers research on age‐related bone loss in women. Furthermore, to detect disease and to monitor therapy, clinical laboratories require reference values derived from an appropriate population sample. Therefore, we determined the age‐specific distribution of values for serum concentrations of calcium, inorganic phosphorus, alkaline phosphatase, bone Gla protein, and parathyroid hormone; for creatinine clearance; for fasting urinary calcium:creatinine ratio; and for 24 h urinary excretion of calcium, hydroxyproline, and cyclic AMP in a population‐based sample of 301 white women. From this sample, a healthy subgroup of 181 women was identified by medical record review. Age‐related effects were seen in all variables except serum calcium and phosphorus. Moreover, substantial differences between the population sample and the healthy subgroup were noted in values for creatinine clearance, serum alkaline phosphatase, and 24 h urinary calcium excretion. These observations may prove useful for assessment of normality in other populations of aging white women.