Dietary Reference Intakes The Essential Guide to Nutrient Requirements (2006) / Chapter Skim
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Pages 188-195
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From page 188... ...
TABLE 1 Dietary Reference Intakes for Vitamin B 12 by Life Stage Group DRI values (mg/day) EARa RDAb AIc ULd males females males females Life stage group 0 through 6 mo 0.4 7 through 12 mo 0.5 1 through 3 y 0.7 0.7 0.9 0.9 4 through 8 y 1.0 1.0 1.2 1.2 9 through 13 y 1.5 1.5 1.8 1.8 14 through 18 y 2.0 2.0 2.4 2.4 19 through 30 y 2.0 2.0 2.4 2.4 31 through 50 y 2.0 2.0 2.4 2.4 2.4e 2.4e 51 through 70 y 2.0 2.0 2.4e 2.4e > 70 y 2.0 2.0 Pregnancy £ 18 y 2.2 2.6 19 through 50 y 2.2 2.6 Lactation £ 18 y 2.4 2.8 19 through 50 y 2.4 2.8 a EAR = Estimated Average Requirement.
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From page 189... ...
PART III: VITAMIN B12 189 VITAMIN B12 V itamin B12 (cobalamin) functions as a coenzyme for a critical reaction that converts homocysteine to methionine and in the metabolism of fatty acids of odd chain length.
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From page 190... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 190 Absorption, Metabolism, Storage, and Excretion Small amounts of vitamin B12 are absorbed by an active process that requires an intact stomach, intrinsic factor (a glycoprotein that the parietal cells of the stom ach secrete after being stimulated by food) , pancreatic sufficiency, and a nor mally functioning terminal ileum.
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From page 191... ...
PART III: VITAMIN B12 191 have atrophic gastritis, although the condition may often go undiagnosed. Thus, it is advisable for those older than 50 years to meet their needs mainly by consuming foods fortified with vitamin B12 or by taking a supplement that contains it.
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From page 192... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 192 Based on data from the Third National Health and Nutrition Examination Survey (NHANES III, 1988–1994) , the highest median intake of B12 from diet and supplements for any life stage and gender group was 17 mg/day; the highest reported intake at the 95th percentile was 37 mg/day.
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From page 193... ...
PART III: VITAMIN B12 193 Bioavailability Data on the bioavailability of vitamin B12 are few. Studies have found the absorption of the nutrient in healthy adults to be 65 percent from mutton, 11 percent from liver, 24–36 percent from eggs, 60 percent from chicken, and 25– 47 percent from trout.
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From page 194... ...
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 194 ing bone-marrow elements. The hematological complications are com pletely reversed by treatment with vitamin B12.
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From page 195... ...
PART III: VITAMIN B12 195 KEY POINTS FOR VITAMIN B12 Vitamin B12 (cobalamin) functions as a coenzyme for a reaction 3 that converts homocysteine to methionine and for a separate reaction in the metabolism of certain fatty acids and amino acids.
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