Vitamin B12 Deficiency: Recognition and Management

 

Am Fam Physician. 2017 Sep 15;96(6):384-389.

  Patient information: A handout on this topic is available at https://familydoctor.org/vitamin-b-12.

Author disclosure: No relevant financial affiliations.

Vitamin B12 deficiency is a common cause of megaloblastic anemia, various neuropsychiatric symptoms, and other clinical manifestations. Screening average-risk adults for vitamin B12 deficiency is not recommended. Screening may be warranted in patients with one or more risk factors, such as gastric or small intestine resections, inflammatory bowel disease, use of metformin for more than four months, use of proton pump inhibitors or histamine H2 blockers for more than 12 months, vegans or strict vegetarians, and adults older than 75 years. Initial laboratory assessment should include a complete blood count and serum vitamin B12 level. Measurement of serum methylmalonic acid should be used to confirm deficiency in asymptomatic high-risk patients with low-normal levels of vitamin B12. Oral administration of high-dose vitamin B12 (1 to 2 mg daily) is as effective as intramuscular administration for correcting anemia and neurologic symptoms. Intramuscular therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms. Absorption rates improve with supplementation; therefore, patients older than 50 years and vegans or strict vegetarians should consume foods fortified with vitamin B12 or take vitamin B12 supplements. Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely. Use of vitamin B12 in patients with elevated serum homocysteine levels and cardiovascular disease does not reduce the risk of myocardial infarction or stroke, or alter cognitive decline.

Vitamin B12 (cobalamin) is a water-soluble vitamin obtained through the ingestion of fish, meat, and dairy products, as well as fortified cereals and supplements.1,2 It is coabsorbed with intrinsic factor, a product of the stomach's parietal cells, in the terminal ileum after being extracted by gastric acid1,2 (Figure 13). Vitamin B12 is crucial for neurologic function, red blood cell production, and DNA synthesis, and is a cofactor for three major reactions: the conversion of methylmalonic acid to succinyl coenzyme A; the conversion of homocysteine to methionine; and the conversion of 5-methyltetrahydrofolate to tetrahydrofolate.1,2

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SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Patients with risk factors for vitamin B12 deficiency should be screened with a complete blood count and serum vitamin B12 level.

C

18

A serum methylmalonic acid level may be used to confirm vitamin B12 deficiency when it is suspected but the serum vitamin B12 level is normal or low-normal.

C

18

Oral and injectable vitamin B12 are effective means of replacement, but injectable therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms.

B

18

Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely.

C

31


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Patients with risk factors for vitamin B12 deficiency should be screened with a complete blood count and serum vitamin B12 level.

C

18

A serum methylmalonic acid level may be used to confirm vitamin B12 deficiency when it is suspected but the serum vitamin B12 level is normal or low-normal.

C

18

Oral and injectable vitamin B12 are effective means of replacement, but injectable therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms.

B

18

Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely.

C

31


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

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Figure 1

Vitamin B12 absorption and transport.

Reprinted with permission from Oh R, Brown DL. Vitamin B12 deficiency. Am Fam Physician. 2003;67(5):981.


Figure 1

Vitamin B12 absorption and transport.

Reprinted with permission from Oh R, Brown DL. Vitamin B12 deficiency. Am Fam Physician. 2003;67(5):981.

In the United States and the United Kingdom, the prevalence of vitamin B12 deficiency is approximately 6% in persons younger than 60 years, and nearly 20% in those older than 60 years.1 Latin American countries have a clinical or subclinical deficiency rate of approximately 40%.1 The prevalence is 70% in

The Authors

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ROBERT C. LANGAN, MD, FAAFP, is the program director at St. Luke's Family Medicine Residency Program, Bethlehem, Pa., and an adjunct associate professor in the Department of Family and Community Medicine at Temple University School of Medicine, Philadelphia, Pa....

ANDREW J. GOODBRED, MD, is a faculty member at St. Luke's Family Medicine Residency Program and an adjunct assistant professor in the Department of Family and Community Medicine at Temple University School of Medicine.

Address correspondence to Robert C. Langan, MD, St. Luke's Hospital, 2830 Easton Ave., Bethlehem, PA 18017 (e-mail: robert.langan@sluhn.org). Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.

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