nutrient whereas another may relate to reducing the risk of chronic degenerative disease, such as certain dementias, cardiovascular disease, cancer, diabetes mellitus, some forms of renal disease, or degenerative arthritis.
Each EAR and AI is described in terms of the selected criterion. For example, the dietary intake set for the RDA for folate for women in the childbearing years is based on a combination of biochemical indicators, but a separate recommendation is made for women capable of becoming pregnant to reduce the risk of a neural tube defect in the offspring if pregnancy occurs.
The potential role of B vitamins and choline in the reduction of disease risk was considered in developing the EARs and AIs for this group of nutrients. The types of evidence considered are described in Chapter 2.
For many of the B vitamins, the use of a single indicator of adequacy was deemed inappropriate. For any one B vitamin, several biochemical values provide information about nutrient status, but adverse effects of inadequate intake may not be observable if only one (or possibly more) of the values is outside its normal range. With the acquisition of new data, such as data relating intake to chronic disease or disability, the choice of the criterion for setting the EAR may change.
Reference nutrient intakes are expressed for 16 life stage groups,2 as listed in Table 1-1 and described in more detail in the first report in this series (IOM, 1997). If data are too sparse to distinguish differences in requirements by life stage or gender group, the analysis may be presented for a larger grouping. Differences will be indicated by gender when warranted by the data.
As with all quantitative estimates, mathematically derived reference intakes may appear to provide much greater precision than the data used to derive them. Conventional rules for rounding of reference intakes are followed in most cases. However, because of the number of assumptions made, particularly in extrapolations, values may have been rounded up to provide a more generous recommendation (or down to provide a more conservative UL).