aged 71 years and older, is 1,176 mg (37.9 mmol)/day and the first percentile of intake is 559 mg (18.0 mmol)/day, which is close to their EAR of 580 mg (18.7 mmol)/day.

The median phosphorus intake for women aged 51 through 70 years is 966 mg (31.2 mmol)/day, based on the adjusted 1994 CSFII intake data. The EAR of 580 mg (18.7 mmol)/day for these women would fall close to the fifth percentile of intake, 599 mg (19.3 mmol)/day. The median phosphorus intake for women, aged 71 years and older, is 859 mg (27.7 mmol)/day, and the tenth percentile of phosphorus intake is 588 mg (19.0 mmol)/day, which is slightly above the EAR of 580 mg (18.7 mmol)/day.

The variance in requirements cannot be determined from the available data. Thus a CV of 10 percent (1 SD) is assumed, resulting in an RDA for phosphorus of 700 mg (22.6 mmol)/day for men and women ages 51 years and older.

Phosphorus Content. Phosphorus content of the term infant at birth is 17.1 g (552 mmol), with 88.3 percent of phosphorus accounted for in bone and water (Fomon et al., 1982). The major physiological adaptations of the mother to meet the increased need for calcium to support fetal growth also should supply the fetus with a sufficient amount of phosphorus. The increased efficiency in intestinal absorption of calcium resulting from increased 1,25(OH)₂D concentrations also will lead to increased intestinal absorption of phosphorus.

Balance studies in 24 pregnant women demonstrated positive phosphorus balance, which increased with length of pregnancy (Heaney and Skillman, 1971). Net phosphorus absorption in these women averaged 70 percent, compared with absorption in the range of 60 to 65 percent typically found in nonpregnant adults (Heaney