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Bioavailability of vitamin B12
1USDA, ARS Western Human Nutrition Research Center, University of California, Davis, CA 95616, USA. Lindsay.allen@ars.usda.gov
Summary
Vitamin B12 deficiency is a global concern, especially for those with low animal-food intake and the elderly. New methods reveal B12 bioavailability decreases with higher intake due to absorption saturation.
Area of Science:
- Nutrition Science
- Human Physiology
- Biochemistry
Background:
- Vitamin B12 deficiency is widespread, affecting diverse age groups and populations globally.
- Malabsorption issues, particularly in the elderly, contribute significantly to vitamin B12 deficiency.
- Existing diagnostic methods for B12 malabsorption, like the Schilling test, lack quantification of bioavailability.
Purpose of the Study:
- To address limitations in current vitamin B12 bioavailability assessment.
- To introduce and evaluate a novel method for measuring vitamin B12 bioavailability.
- To investigate the dose-dependent nature of vitamin B12 absorption.
Main Methods:
- Utilizing a newer, low-dose radioactivity method with (14)C-labeled B12.
- Measuring isotope excretion in urine and feces via accelerator mass spectrometry.
- Analyzing the degradation of unabsorbed vitamin in the intestine.
Main Results:
- The new method quantifies percent bioavailability, unlike older techniques.
- Demonstrated that unabsorbed vitamin B12 undergoes degradation within the intestine.
- Established an inverse relationship between vitamin B12 dose consumed and its percent bioavailability due to absorption saturation.
Conclusions:
- Vitamin B12 bioavailability is dose-dependent, with saturation of active absorption occurring even at typical dietary intake levels.
- Findings necessitate re-evaluation of bioavailability values, dietary requirements, and intake-status relationships for vitamin B12.
- The developed method offers a more accurate assessment of vitamin B12 bioavailability.
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