phorus, as it falls below the first percentile of intake of 773 mg (24.9 mmol)/day (see ). The EAR of 1,055 mg (34 mmol) for pregnant women ages 14 through 18 years falls slightly above the fifth percentile of intake of 1,012 mg (32.6 mmol)/day.

Special Considerations

Adolescent Mothers and/or Multiple Fetuses. It is not known whether phosphorus requirements are increased in the adolescent mother and in mothers pregnant with more than one fetus. These conditions lead to increased maternal or fetal needs for phosphorus that may not be met by increased intestinal absorption. The mediating role of maintaining calcium homeostasis is also important in these situations: a diet insufficient in calcium may lead to increased PTH concentrations and decreased renal tubular reabsorption of phosphorus.

Lactation
Indicators Used to Set the EAR

Human Milk. Concentrations of phosphorus in human milk range from approximately 3.9 to 5.1 mmol/liter (12.1 to 15.8 mg/dl) and decrease as lactation progresses (Table 5-2). Assuming a milk production of 780 ml/day, a lactating woman may lose approximately 90 to 120 mg (2.9 to 3.9 mmol)/day of phosphorus in her milk. No studies have investigated the effect of varying phosphorus intake on phosphorus homeostasis during lactation.

Serum Pi. Despite the loss of phosphorus in milk, serum phosphorus concentrations in lactating women are in the high-normal or above-normal range, and they are higher in lactating women than in nonlactating women (Figure 5-2) (Byrne et al., 1987; Chan et al., 1982a; Cross et al, 1995a; Dobnig et al., 1995; Kalkwarf et al., 1996; Kent et al., 1990; Lopez et al., 1996; Specker et al., 1991a). This high serum phosphorus occurs at a time when there is an increase in bone resorption that appears to be related to non-dietary factors (see Chapter 4). The elevated serum phosphorus is due in whole or part to the fall in serum PTH which leads to high serum Pi.

EAR and RDA Summary for Lactation

Currently no evidence supports that phosphorus requirements are



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