I have noticed several commonalities among patients with vitamin B12 levels <400 pg/mL. In addition to fatigue, paresthesias, and decreased concentration, these patients also have irritable bowel syndrome (IBS). The IBS symptoms typically improve after supplementation. I am not able to find any documentation in the literature that supports or explains this improvement in the bowel function. — Melissa Garrison, ARNP, Sun City Center, Fla.

A literature search found nothing on IBS and vitamin B12. Interestingly, my research showed that the relationship between B12 deficiency and bowel function was the reverse of what was suggested. Vitamin B12 deficiency is common in patients with celiac or Crohn’s disease, two bowel disorders that decrease absorption of vitamin B12.

IBS is a functional bowel disorder, meaning that symptoms occur despite all test results being normal. Since the demand for B12 increases whenever cells are rapidly turning over (common during periods of damage or healing), I would want to know that patients were fully evaluated for their bowel symptoms prior to receiving the diagnosis of IBS. — Rebecca H. Bryan, APRN, CNP (153-07)