97 to 98 percent of the individuals in the group (therefore, for B₁₂ the RDA is 120 percent of the EAR).

No single indicator was judged to be a sufficient basis for deriving an EAR for adults. It was not deemed appropriate to base the EAR on an examination limited to studies that provided data on mean cell volume (MCV) or serum B₁₂ or any other single laboratory value. Data on men and women were examined together because of small numbers. Three general approaches were considered to derive the EAR for adults: determination of the amount of B₁₂ needed to maintain adequate hematological status (as measured by stable hemoglobin value, normal MCV, and normal reticulocyte response) and serum B₁₂ values in persons with pernicious anemia or with known intakes that were very low in dietary B₁₂; use of daily B₁₂ turnover to estimate the amount of B₁₂ needed to maintain body stores at a specified level; and estimation of the dietary B₁₂ intake by healthy adults that corresponds to adequate serum values of B₁₂ and of MMA.

The first approach was chosen as the primary method for deriving an EAR because it is the only approach for which there are sufficient and reliable data for estimating need. A low serum B₁₂ value in persons with pernicious anemia was assumed to indicate incomplete response to treatment.

Primary Criterion: Maintenance of Hematological Status and Serum B₁₂ Values. The primary method used to derive the EAR for adults estimates the amount of B₁₂ needed for the maintenance of hematological status and serum B₁₂ values, primarily by using data derived from patients with pernicious anemia in remission. Data from studies of vegetarians were also examined to determine whether they