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TABLE 9-7 Studies of Individuals with Low Vitamin B12 Intake Considered in Setting the Estimated Average Requirement for B12 for Adults

Reference

Description

Dietary B12 Intake

Suggested dietary B12average requirement > 1.5 µg/d

Stewart et al., 1970

1 Hindu woman with megaloblastic anemia

0.5 µg/d (analyzed homogenate)

Narayanan et al., 1991

10 subjects with serum B12 values below the 2.5 percentile (< 120 pmol/L [162 pg/mL]) not caused by disease or vegetarianism

1.5 ± 0.4 (SDc) µg/d of B12 (range 0.6–1.9)

Suggested dietary B12 average requirement > 1.0 µg/d

Winawer et al., 1967

1 64-y-old vegan with B12-deficient megaloblastic anemia, gastritis on biopsy, and normal gastric acidity

Assumed to be negligible

Jathar et al., 1975

7 East Indian lactovegetarians

0.3–0.8 µg/d of B12 from milk, assuming that it was not boiled

Baker and Mathan, 1981

4 East Indians with B12 deficiency anemia secondary to diet

NAd

a p.o. = by mouth.

b Based on USDA data (URL http://www.nal.usda.gov/fnic/foodcomp/).

appear to be impaired, the combination of stores and absorbed crystalline B12 may cover needs for an extended period.

The estimates above for the period of protection afforded by body stores are consistent with the periods required to develop overt signs of B12 deficiency after a total gastrectomy; for example, megaloblastic anemia has been typically diagnosed 2 to 5 years after a total gastrectomy (Chanarin, 1990).



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