Two points were primary in dividing early childhood into two groups. First, the greater velocity of growth in height for children ages 1 through 3 years of age compared with those 4 through 5 years of age provides a biological basis for dividing this period of life. Second, because children in the United States and Canada begin to enter the public school system starting at age 4 years, ending this life stage prior to age 4 years seemed appropriate so that food and nutrition policy planners have appropriate targets and cutoffs for use in program planning.
Data are sparse for indicators of nutrient adequacy on which to derive DRIs for these early years of life. In these cases, extrapolation from data on 0- to 6-month-old infants has been employed (IOM, 1997, 1998, 2000b, 2001, 2002a).
Major biological changes in the velocity of growth and changing endocrine status occur in children 4 through 8 or 9 years of age (the latter depending on onset of puberty in each gender); therefore, the category of 4 through 8 years is appropriate. For many nutrients, a reasonable amount of data is available on nutrient intake and on various criteria for adequacy (e.g., nutrient balance measured in children 5 through 7 years of age) that can be used as the basis for the EARs and AIs for this life stage group.
Because current data support younger ages for pubertal development, it was determined that the adolescent age group should begin at 9 years. The mean age of onset of breast development (Tanner Stage 2) for white girls in the United States is 10.0 ± 1.8 years (SD); this is a physical marker for the beginning of increased estrogen secretion (Herman-Giddens et al., 1997). In African-American girls, the onset of breast development is earlier (mean 8.9 ± 1.9 years). The reason for the observed racial differences in the age at which girls enter puberty is unknown. The onset of the growth spurt in girls begins before the onset of breast development (Tanner, 1990); the age group of 9 through 13 years allows for the early growth spurt of African-American girls.
For boys the mean age of initiation of testicular development is 10.5 to 11 years, and their growth spurt begins 2 years later (Tanner,