Can a vitamin B12 (B12) deficiency cause constipation?

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Last updated: June 20, 2025View editorial policy

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From the Guidelines

Vitamin B12 deficiency is not directly associated with constipation as a primary cause, according to the most recent and relevant evidence. The management of constipation, as outlined in the study by Nightingale JMD, et al. 1, focuses on dietary adjustments, bulk-forming laxatives, osmotic laxatives, and stimulant laxatives, without mentioning vitamin B12 deficiency as a contributing factor. Constipation may be a problem in early stages of certain diseases, but it is rarely present when more severe conditions occur, and its management is approached through various laxative types and dietary changes, as discussed in the study 1.

When considering the potential effects of vitamin B12 deficiency on the body, it's crucial to prioritize the most recent and highest-quality evidence. While B12 plays a significant role in nerve function and the formation of red blood cells, its direct link to constipation as a primary cause is not supported by the provided study 1. Instead, the focus for managing constipation remains on ensuring adequate fiber and fluid intake, and the use of appropriate laxatives.

Key points for managing constipation, based on the evidence from Nightingale JMD, et al. 1, include:

  • Ensuring an adequate intake of fiber and fluid
  • Using bulk-forming laxatives such as unprocessed wheat bran or methylcellulose
  • Considering osmotic laxatives like macrogols, lactulose, or magnesium salts for increased water in the large bowel
  • Adding stimulant laxatives if there's an inadequate response to osmotic laxatives, while being cautious of their potential side effects

It's essential to consult a healthcare provider for personalized advice on managing constipation and addressing any underlying nutritional deficiencies, including vitamin B12. However, based on the provided evidence, the primary approach to constipation does not involve vitamin B12 supplementation as a first-line treatment.

From the Research

Vitamin B12 Deficiency and Constipation

  • Vitamin B12 deficiency can cause a variety of symptoms, including gastrointestinal issues 2, 3.
  • While diarrhea is mentioned as a possible symptom of vitamin B12 deficiency in some studies 2, constipation is also noted in specific cases 3.
  • A 20-year-old female patient with vitamin B12 deficiency due to pernicious anemia presented with constipation, among other symptoms 3.
  • However, constipation is not a widely reported or emphasized symptom of vitamin B12 deficiency in the provided studies.
  • The relationship between vitamin B12 deficiency and constipation may be complex and influenced by various factors, including the underlying cause of the deficiency and individual patient characteristics 4, 5, 6.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

A Routine CBC Leads to a Nonroutine Diagnosis.

Adolescent medicine (Philadelphia, Pa.), 1996

Research

Vitamin B12 deficiency in patients with urinary intestinal diversion.

International journal of urology : official journal of the Japanese Urological Association, 1997

Research

Vitamin B12 deficiency.

Vitamins and hormones, 2022

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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