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Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
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N
Estimation of the Period Covered by Vitamin B12 Stores

As indicated in Chapter 9, it is possible to estimate the length of time body stores of vitamin B12 held in reserve will maintain adequate nutriture when dietary intake is nonexistent as a result of adopting a vegan or similar diet very low in B12 or when decreased absorption of vitamin B12 occurs as a result of atrophic gastritis or pernicious anemia.

This estimate is based on being able to ascertain what the expected turnover rate will be (0.1, 0.15, and 0.2 percent have been found experimentally to occur). It has been estimated that in individuals with normal absorption and reabsorption rates for vitamin B12, the daily turnover is 0.1 percent per day. For individuals with pernicious anemia, who cannot absorb or reabsorb vitamin B12, the turnover rate is about 0.2 percent of the body pool or stores per day. As individuals develop various degrees of atrophic gastritis, it is possible that a turnover rate of 0.15 percent is appropriate.

To estimate how long body stores of vitamin B12 can be depended on to maintain health, it is also necessary to know the lowest pool size of vitamin B12 consistent with health, which could be considered to be the threshold before which signs of inadequate B12 would begin to occur. As is indicated in Chapter 9, this has been estimated to be approximately 300 µg (Bozian et al., 1963).

By calculating the ratio of the total body stores of vitamin B12 to this assumed threshold (or to a lower threshold if expected because of differences in individual requirements), it is possible to estimate how long body stores will meet the needs of the individual.

Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
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TABLE N-1 Table of Ratiosa Used to Estimate the Extent of Protection from Vitamin B12 Stores

 

Initial Store, mg

Vitamin B12 Threshold, µg

1

2

3

4

5

6

7

8

9

10

350

3

6

9

11

14

17

20

23

26

29

300

3

7

10

13

17

20

23

27

30

33

250

4

8

12

16

20

24

28

32

36

40

200

5

10

15

20

25

30

35

40

45

50

150

7

13

20

27

33

40

47

53

60

67

100

10

20

30

40

50

60

70

80

90

100

a This represents the initial vitamin B 13 stores divided by the level of stores at which signs of vitamin B12 deficiency may become evident.

Table N-1 provides the ratio of the expected stores of an individual (in milligrams) to the threshold level of stores at which signs of vitamin B12 deficiency may appear. Usually the threshold value is not known, but studies suggest that it may be approximately 300 µg of vitamin B12 for adults (Bozian et al., 1963).

Tables N-2 and N-3 give the expected length in days (Table N-2) or years (Table N-3) for a given turnover rate and ratio from Table N-1 that body stores of vitamin B12 will sustain health in the individual. For example, from Table N-1 the ratio for an initial store of 3 mg of vitamin B12 and a threshold of 300 µg of vitamin B12 is 10. If the turnover rate is 0.1, the store would be expected to last 2,303 days, or 6.3 years.

REFERENCE

Bozian RC, Ferguson JL, Heyssel RM, Meneely GR, Darby WJ. 1963. Evidence concerning the human requirement for vitamin B12. Use of the whole body counter for determination of absorption of vitamin B12. Am J Clin Nutr 12:117– 129.

Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×

TABLE N-2 Time in Days until Vitamin B12 Threshold Is Reached

 

Turnover Rate

Ratio of Initial Stores to Threshold, from Table N-1

0.1

0.15

0.2

70

4,248

2,832

2,124

60

4,094

2,730

2,047

50

3,912

2,608

1,956

40

3,689

2,459

1,844

30

3,401

2,267

1,701

20

2,996

1,997

1,498

17

2,833

1,889

1,417

16

2,773

1,848

1,386

15

2,708

1,805

1,354

14

2,639

1,759

1,320

13

2,565

1,710

1,282

12

2,485

1,657

1,242

11

2,398

1,599

1,199

10

2,303

1,535

1,151

9

2,197

1,465

1,099

8

2,079

1,386

1,040

7

1,946

1,297

973

6

1,792

1,195

896

5

1,609

1,073

805

4

1,386

924

693

3

1,099

732

549

Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×

TABLE N-3 Table of Time in Years until Vitamin B12 Threshold Below Which Deficiency Signs May Occur Is Reached

 

Turnover Rate

Ratio of Initial Stores to Threshold, from Table N-1

0.1

0.15

0.2

70

11.6

7.8

5.8

60

11.2

7.5

5.6

50

10.7

7.1

5.4

40

10.1

6.7

5.0

30

9.3

6.2

4.7

20

8.2

5.5

4.1

17

7.8

5.2

3.9

16

7.6

5.1

3.8

15

7.4

4.9

3.7

14

7.2

4.8

3.6

13

7.0

4.7

3.5

12

6.8

4.5

3.4

11

6.6

4.4

3.3

10

6.3

4.2

3.2

9

6.0

4.0

3.0

8

5.7

3.8

2.8

7

5.3

3.6

2.7

6

4.9

3.3

2.5

5

4.4

2.9

2.2

4

3.8

2.5

1.9

3

3.0

2.0

1.5

Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×
Page 527
Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×
Page 528
Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×
Page 529
Suggested Citation:"N Estimation of the Period Covered by Vitamin B12 Stores." Institute of Medicine. 1998. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: The National Academies Press. doi: 10.17226/6015.
×
Page 530
Next: O Biographical Sketches »
Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline Get This Book
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Since 1941, Recommended Dietary Allowances (RDAs) has been recognized as the most authoritative source of information on nutrient levels for healthy people. Since publication of the 10th edition in 1989, there has been rising awareness of the impact of nutrition on chronic disease. In light of new research findings and a growing public focus on nutrition and health, the expert panel responsible for formulation RDAs reviewed and expanded its approach--the result: Dietary Reference Intakes.

This new series of references greatly extends the scope and application of previous nutrient guidelines. For each nutrient the book presents what is known about how the nutrient functions in the human body, what the best method is to determine its requirements, which factors (caffeine or exercise, for example) may affect how it works, and how the nutrient may be related to chronic disease.

This volume of the series presents information about thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline.

Based on analysis of nutrient metabolism in humans and data on intakes in the U.S. population, the committee recommends intakes for each age group--from the first days of life through childhood, sexual maturity, midlife, and the later years. Recommendations for pregnancy and lactation also are made, and the book identifies when intake of a nutrient may be too much. Representing a new paradigm for the nutrition community, Dietary Reference Intakes encompasses:

  • Estimated Average Requirements (EARs). These are used to set Recommended Dietary Allowances.
  • Recommended Dietary Allowances (RDAs). Intakes that meet the RDA are likely to meet the nutrient requirement of nearly all individuals in a life-stage and gender group.
  • Adequate Intakes (AIs). These are used instead of RDAs when an EAR cannot be calculated. Both the RDA and the AI may be used as goals for individual intake.
  • Tolerable Upper Intake Levels (ULs). Intakes below the UL are unlikely to pose risks of adverse health effects in healthy people.

This new framework encompasses both essential nutrients and other food components thought to pay a role in health, such as dietary fiber. It incorporates functional endpoints and examines the relationship between dose and response in determining adequacy and the hazards of excess intake for each nutrient.

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