C. Ho et al., Practitioners' guide to meeting the vitamin B-12 - Recommended Dietary Allowance for people aged 51 years and older, J AM DIET A, 99(6), 1999, pp. 725-727
In response to research findings that 10% to 30% of people aged 51 years an
d older may have protein-bound vitamin B-12 malabsorption, the National Aca
demy of Sciences' Institute of Medicine recommends that these people consum
e a majority of the new Recommended Dietary Allowance (RDA) of 2.4 mu g/day
in its synthetic form rather than in its food form. Protein-bound vitamin
B-12 malabsorption in older adults has been attributed to reduced pepsin ac
tivity and gastric acid secretion, which interfere with cleavage of vitamin
B-12 from dietary protein before absorption. Unlike patients with pernicio
us anemia, most people with protein-bound vitamin B-12 malabsorption produc
e intrinsic factor and have the ability to absorb synthetic vitamin B-12 no
rmally. Early diagnosis is necessary to prevent the untoward effects of vit
amin B-12 deficiency. A thorough assessment of vitamin B-12 status entails
measurement of multiple biochemical assessment indexes, including serum vit
amin B-12, methylmalonic acid, and homocysteine concentrations. Dietitians
and other health care professionals should be aware of the prevalence of vi
tamin B-12 deficiency in older adults and be familiar with sources of synth
etic vitamin B-12 to facilitate implementation of the new RDA.