zinc, thiamin, vitamin B6, and vitamin E fall below the RDA. At 1,800 kcal, predicted intakes fall below the RDAs for all the nutrients listed above plus riboflavin, folate, phosphorus, and iron.
Several cautions are necessary in interpreting these patterns:
The RDAs for most nutrients include a wide margin of safety, so intakes below the RDAs do not necessarily indicate inadequacy. Of the nutrients for which predicted average intake is below the RDA, most intake estimates range from 73 to 97% of the RDA, except intakes for zinc, which are 67 and 55% of the RDA (at 2,200 and 1,800 kcal, respectively) and for calcium and vitamin B6, which are 60 and 67%, respectively (each at 1,800 kcal). There is also a wide range in the nutrient densities used to generate the averages shown in Table 9-3. Even if the average predicted intake of a given nutrient is at or above the RDA, the intakes of a substantial proportion of the population would fall below that level.
The margin of safety in the RDA varies by nutrient. As shown in Table 9-1, for example, the increment in the RDA for vitamin B6 for lactation is more than five times the estimated secretion of this vitamin in milk. In contrast, the increment for folate is less than two times the estimated secretion.
Overt signs of deficiency are extremely rare in the United States, even for nutrients with small safety margins.
Nutrient densities of diets consumed by lactating women are likely to differ from those for U.S. women as a whole. Inspection of data for lactating women shown in Chapter 4 indicates that densities of calcium and vitamin A, for example, are 40 to 50% higher in the diets of the lactating women surveyed than the values shown in Table 9-3, possibly because greater quantities of milk products are consumed. It could be argued either than women who choose to breastfeed are women who ordinarily have high nutrient intakes, or that women consume more nutrient-rich foods when breastfeeding. Whatever the case, higher than average densities of some nutrients in diets of the few lactating women studied to date are not grounds for complacency, because the samples in these studies were generally not randomly selected. There is no evidence that the same nutrient intakes would pertain to breastfeeding women in less affluent or less educated groups.
Keeping these cautions in mind, this subcommittee attempted to determine which nutrients are most likely to be in short supply in the diets of lactating women, relative to the RDAs, and the consequences of any such shortfalls.
Calcium is clearly a concern because it is difficult for many lactating women to consume the RDA of 1,200 mg/day, especially if milk products are not a major part of the diet. This may be even more relevant for women younger than age 25 who breastfeed, since the calcium content of bones is ordinarily