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*
Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111 and
Ilsan Paik Hospital, School of Medicine, Inje University, Kyungkido, Korea
3To whom correspondence should be addressed U.S. Department of Agriculture, Human Nutrition Research Center on Aging, Tufts University, 711 Washington Street, Boston, MA 02111. E-mail: russell{at}hnrc.tufts.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • vitamin B-12 • vitamin B-12 bioavailability • vitamin B-12 absorption • humans
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). In
the 1999 Recommended Dietary Allowance report, it was assumed that 50%
of dietary vitamin B-12 can be absorbed by healthy adults; however, it
was noted that data on vitamin B-12 absorption from specific foods are
scanty, and indeed, absorption has been tested only from mutton, eggs,
chicken, liver and trout (Doscherholmen et al. 1975
, 1978
and 1981
, Heysell et al. 1966
). Nothing is directly
known of vitamin B-12 bioavailability from dairy products or from
fortified grain products, although a recent epidemiologic study on the
Framingham offspring suggested that vitamin B-12 in milk and fortified
breakfast cereal may be better absorbed than vitamin B-12 from other
food sources (Tucker et al. 2000
) In the present study, we directly measured vitamin B-12 absorption from water, milk and fortified bread in adult subjects by using extrinsically (58Co) labeled vitamin B-12 and a whole body gamma-ray counter/spectrophotometer.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Sixteen healthy volunteers aged 60–78 y (nine women and seven men)
participated in the study. Subjects over the age of 60 y were
chosen to minimize any possible variability due to change in body
composition with age. Subjects were screened to ensure they had normal
serum vitamin B-12 levels and normal gastric pH. For gastric pH
measurements, a Dobhoff tube was passed into the stomach of each
subject after an overnight fast. After a 10-min equilibration period,
10 mL of gastric fluid was withdrawn for pH measurement. The gastric pH
was found to be 
2.5 in all subjects.
Experimental Protocol
Preparation of vitamin B-12 doses. We dissolved 0.25 µ g 58Co-labeled vitamin B-12 (29.6 kBq, 0.8 µCi) (Medi-Physics Inc./Amersham, Arlington Heights, IL) 5 mL of distilled water in a glass tube. The tube was inverted several times and then was allowed to stand for 10 min before repeating multiple inversions. Four mL of distilled water or pasteurized milk (2%) was added to the solution, and inversions were repeated. To prepare the fortified bread, two slices of white bread were laid on a flat surface, and microliter amounts of the 58Co-labeled vitamin B-12-in-water solution were applied to 10 evenly spaced regions of the individual slices with a micropipette. The bread was air dried, wrapped in foil and then frozen at -70°C until use within 48 h. The bread was allowed to thaw at room temperature on the evening before consumption.
Study design. Subjects were randomly allotted to one of the three experimental groups. After an overnight fast, subjects received one dose of 0.25 µg radioactive cyanocobalamin 58Co in either water, milk or fortified bread. Five microcuries (185 kBq) of radioactive 51Cr was administered with the vitamin preparation in the form of sodium chromate as a stool marker to indicate fecal clearance of any unabsorbed label from the oral dose. Subjects receiving the vitamin B-12 in water or fortified bread (containing 0.1 µg vitamin B-12) received an additional 50 mL of distilled water at the time of dose administration. Similarly, subjects receiving the vitamin B-12–fortified milk received an additional 50 mL of 2% milk (containing 0.2 µg vitamin B-12) at the time of dose administration. An initial whole body count was performed 30 min after ingestion of the radioactive dose. After the initial body count, all subjects received a standard meal [709 kcal (2966 kJ), 0.4 µg B-12] and were discharged. The levels of both isotopes were measured at 7 and 14 d after dosing using a whole body gamma ray counter/spectrometer.
Whole body counting technique.
The whole body gamma ray counter/spectrometer at the U.S. Department of
Agriculture Human Nutrition Research Center on Aging at Tufts
University consists of two large thallium-activated sodium iodide
crystal gamma-ray detectors positioned 39 cm above and 7 cm below a
thin polyvinylchloride bed. A tracking system carries both detectors
1.91 m via a computer-operated, variable speed stepping motor.
The variable speed of the scan makes the detectors move faster when
they are over the middle section of the body, resulting in a uniform
detection efficiency throughout the length of the body. To reduce
interference from natural background, the volunteer, the bed, the
detectors and the scanning system are enclosed in a room made from
15-cm-thick pre-1945 steel on all sides and lined with 5-mm lead
shielding. The duration of the scan is 20 min. The detection system is
connected to a data acquisition system, which records spectral energy
data of the emitted gamma-rays. This feature allows for better
separation from interfering radiation sources and for the simultaneous
measurement of several isotopes, separated by energy, such as
58Co and 51Cr. The whole body gamma ray
counter/spectrometer offers detection of natural and administered
radioisotopes in vivo in the whole body and therefore direct
measurement of uptake, absorption and retention of nutrients labeled
with a gamma emitter without the use and the complexity of
excreta-recovery methods (Kehayias et al. 1997
,
Shipp et al. 1987
). Absorption of vitamin B-12 was
calculated by comparing the measured 58Co counts at dosing
and at 14 d after a correction for half-life and photon
self-absorption in the body.
Statistical Analysis
The significance of differences were determined by analysis of variance. Calculations were performed with SAS software (PROC GLM Version 8.0; SAS Institute, Cary, NC). Results are expressed as the mean percentages of dose absorbed with simultaneous 95% confidence intervals (CI)4 based on Tukey’s honestly significant differences.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Group 1 (vitamin B-12 in water) consisted of three men and three
women, whereas group 2 (vitamin B-12 in milk) and group 3 (vitamin B-12
in fortified bread) each consisted of three women and two men.
51Cr counting indicated that none of the
volunteers had any isotope remaining in the gastrointestinal tract by d
14. Vitamin B-12 absorptions were 55% (95% CI 41–67%) from water,
65% (95% CI 51–79%) from milk and 55% (95% CI 41–69%) from
fortified bread, values that did not differ.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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and 1985
,
International Committee for Standardization in Hematology 1981
) studied the effect of patient thickness to the
attenuation of the gamma-rays assuming the total concentration of
57Co-labeled vitamin B-12 activity was in the
liver. The error due to the self-absorption correction was
minimized in our experiment by using the higher-energy isotope
(58Co-emitting photons at 810.5 Kev).
The absorption of the extrinsic vitamin B-12 label from milk and
fortified bread was found to be high: 55–65%. These percentages
compare well with the reported absorbability of vitamin B-12 from meat.
Using similar whole body counting or stool counting techniques, 65% is
absorbed from mutton, 60% is absorbed from chicken, 39% is
absorbed from trout and 24–36% is absorbed from eggs
(Doscherholmen et al. 1975
, 1978
and 1981
). Our results
of high body retention of an extrinsic B-12 label from milk and
fortified bread are not surprising given the recent report by
Tucker et al. (2000
), which showed stronger associations
between serum vitamin B-12 and intake of vitamin B-12 (by quintiles)
from milk and fortified cereal than from other food products in the
Framingham Offspring Study. Similar strong associations between dairy
foods and vitamin B-12 status were also reported by others
(Miller et al. 1991
).
Our study was conducted in people over the age of 60 y who did not
have atrophic gastritis, as judged by normal gastric pH. Between 10 and
30% of elderly people in the United States are judged to have atrophic
gastritis, which limits the bioavailability of food-bound vitamin
B-12 due to the inability to dissociate the vitamin from food protein
and due to bacterial uptake of any vitamin that is freed
(Hurwitz et al. 1997
, Krasinski et al. 1986
). Crystalline vitamin B-12 absorption is normal in most
people with atrophic gastritis, because intrinsic factor is not lowered
to a critical degree (Dawson et al. 1984
,
Doscherholmen et al. 1976
and 1981
, Jones et al. 1987
, King et al. 1979
, Suter et al. 1993
). It is not known how efficient the absorption of vitamin
B-12 from milk or fortified bread would be in elderly subjects with
atrophic gastritis; however, it has been presumed that vitamin B-12
bioavailability from a fortified cereal product would be as high as
that from a dietary supplement in subjects with atrophic gastritis,
because crystalline vitamin B-12 is sprayed onto such products.
Nevertheless, it is possible that a high fiber content could affect the
bioavailability of vitamin B-12 in cereals (Cullen and Oace, 1978
). These issues are important and in need of additional
study, given the relatively high prevalence of low serum vitamin B-12
levels in the U.S. elderly population: in NHANES III, 13% of people
over the age of 70 y had serum vitamin B-12 levels of <250 pg/mL
(184 pmol/L) (National Center for Health Statistics 1988
). For now, it is warranted to encourage elderly people to
consume products fortified in vitamin B-12 as well as milk [which
contains 1.0 µg in 1 cup (236 mL)] to ensure B-12 adequacy.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 This project was funded in part from a grant by the National Dairy Council and by USDA/ARS under Agreement No.
58–1950-9–001.
4 Abbreviation used: CI, confidence interval.
Manuscript received August 23, 2000. Initial review completed October 5, 2000. Revision accepted November 21, 2000.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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