The dietary intake of phosphorus in the United States is high relative to calcium. Intake estimates from the 1989-1991 Continuing Surveys of Food Intakes by Individuals conducted by the U.S. Department of Agriculture show that for both men and women, median calcium intakes do not meet the 1989 Recommended Dietary Allowances (RDAs) for most age groups over 10 y of age, whereas phosphorus intakes exceed the RDAs for most age groups. The use of phosphorus-containing food additives in the processing of foods contributes substantially to the daily phosphorus intake, and their use is increasing. Because much of the phosphorus through food additive use is not reflected in the estimates of phosphorus intakes derived from national food consumption surveys, these estimates underestimate true dietary intakes of phosphorus. High phosphorus intake has been shown to cause secondary hyperparathyroidism and bone loss in several animal models. High phosphorus, low calcium consumption consistent with current observed intake levels resulted in changes in calcium-regulating hormones that were not conducive to optimizing peak bone mass in young women. Evidence that such high phosphorus intakes may impair synthesis of the active metabolite of vitamin D and disrupt calcium homeostasis particularly in older women are discussed.