men and women. Median energy intakes ranged from 1,507 to 2,109 kcal/day for men and women (51–70 years) to 1,356 to 1,978 kcal/day (> 70 years) based on NHANES III data (IOM, 2002/2005). The average of these ranges was used to extrapolate from younger adults who consumed more energy than older adults. However, for potassium the intake was not adjusted down for older adults because of the increased risk of elevated blood pressure with aging.

It is known that the placenta actively transports certain nutrients from the mother to the fetus against a concentration gradient (Hytten and Leitch, 1971). However, for many nutrients, including sodium and potassium, experimental data that could be used to set an EAR and RDA or an AI for pregnancy are lacking. In these cases, the potential increased need for these nutrients during pregnancy is based on theoretical considerations, including obligatory fetal transfer, if data are available, and on increased maternal needs related to increases in energy or protein metabolism, as applicable. Because there was insufficient evidence to suggest that an AI for potassium or sodium during pregnancy should be quantitatively different from that of nonpregnant women and because pregnant women consumed within the energy range of nonpregnant women, an AI was not set differently for pregnant women.

It is assumed that the total nutrient requirement for sodium, potassium, and water for lactating women equals the requirement for nonpregnant, nonlactating women of similar age plus an increment to cover the amount needed for milk production. Details are provided in each nutrient chapter.

Reliable and valid methods of food composition analysis are crucial in determining the intake of a nutrient needed to meet a requirement. For nutrients such as sodium, estimating intake has been challenging because of the difficulty in assessing the amount of sodium chloride (salt) added to foods during cooking and during eating.