Diet and Bone Changes in Pregnancy and Lactation
Over the past 80 years, strong interest has centered on the question as to whether the net effect of pregnancy and lactation on the human skeleton is positive, negative, or zero. Pregnancy and lactation are times of high nutrient demand. During the course of a normal, full-term, singleton pregnancy, approximately 25 g (range 13-33 g) of calcium is deposited in the skeleton of the fetus (Kovacs and Kronenberg, 1997), and between 280 and 400 mg of calcium per day is expressed in breast milk (Kovacs and Kronenberg, 1997). Along with calcium, 16 mg of phosphorus, 750 mg of magnesium, and 50 mg zinc are concomitantly deposited in the fetus, primarily during the last trimester (Prentice and Bates, 1994). During the „rst 6 months of lactation, approximately 140 mg of calcium, 70 mg of phosphorus, 3 mg of magnesium, and 0.4 mg of zinc are deposited in the growing infant skeleton. Table 20.1 summarizes the recommended intakes set by the dietary reference intakes for these nutrients for women of child-bearing age (Institute of Medicine, Food and Nutrition Board, 1997).