In an adult patient with macrocytic anemia, low serum vitamin B12 and neurologic signs, can vitamin B12 deficiency cause a reduction in left ventricular ejection fraction?

B12 Deficiency and Reduced LVEF: The Evidence Does Not Support a Direct Causal Link

While vitamin B12 deficiency causes well-documented hematological and neurological complications, the provided evidence does not establish that B12 deficiency directly causes a reduction in left ventricular ejection fraction (LVEF). The available guidelines and research focus exclusively on anemia, neurological manifestations, and cognitive symptoms—not cardiac dysfunction or heart failure.

What the Evidence Actually Shows

The comprehensive guidelines from bariatric surgery monitoring 1 and endocrinology societies 2 consistently describe B12 deficiency presenting with:

• Macrocytic anemia with megaloblastic changes
• Neurological symptoms: peripheral neuropathy, subacute combined degeneration of the spinal cord, sensory ataxia, impaired proprioception, gait disturbances 1
• Cognitive impairment: "brain fog," memory loss, dementia 2
• Hematological abnormalities: pancytopenia, hypersegmented neutrophils, ineffective erythropoiesis 3

Recent clinical studies 4, 5, 3, 6 describe patients with severe B12 deficiency presenting with profound anemia (hemoglobin as low as 9.7 g/dL), fatigue, and functional decline—but none mention cardiac dysfunction or reduced LVEF as a manifestation.

The Cardiovascular Evidence Gap

One guideline 7 discusses B vitamins (including B12) in stroke prevention, noting that B12 supplementation may reduce stroke risk by lowering homocysteine levels. However, this same source explicitly states that "use of vitamin B12 in patients with elevated serum homocysteine levels and cardiovascular disease does not reduce the risk of myocardial infarction" 8. Critically, there is no mention of B12 deficiency causing heart failure or reduced LVEF.

Clinical Reasoning: Why LVEF Might Drop in B12-Deficient Patients

If a patient with B12 deficiency has reduced LVEF, consider these more likely explanations:

1. Severe anemia itself can cause high-output cardiac stress and may unmask underlying cardiac disease, but this is a consequence of anemia (from any cause), not B12 deficiency per se

2. Coexisting conditions: The patient may have independent cardiovascular disease coincidentally present alongside B12 deficiency

3. Thiamine deficiency: Often confused with B12 deficiency, thiamine (B1) deficiency causes wet beriberi with high-output heart failure and can reduce LVEF—this is well-established but distinct from B12 deficiency 1

Important Caveats

• Don't miss thiamine deficiency: If you're seeing cardiac dysfunction in a patient with suspected nutritional deficiency, consider thiamine deficiency (especially in alcoholism, malabsorption, or post-bariatric surgery) 1

• Severe anemia of any cause can stress the cardiovascular system and may precipitate heart failure in patients with underlying cardiac disease

• The absence of evidence is not evidence of absence: While no studies in this evidence set link B12 deficiency to reduced LVEF, rare case reports may exist outside this literature

What You Should Do

For your patient with macrocytic anemia, low B12, and neurologic signs:

1. Treat the B12 deficiency immediately with hydroxocobalamin 1 mg IM on alternate days until no further improvement (given neurological involvement) 1

2. Seek urgent specialist advice from neurology and hematology for neurological symptoms 1

3. Investigate the reduced LVEF separately as an independent problem—obtain echocardiography, assess for ischemic heart disease, valvular disease, or other cardiomyopathies

4. Consider thiamine deficiency if there are risk factors (alcohol use, malabsorption, poor nutrition) and treat empirically if suspected

5. Evaluate for other causes of anemia that might be contributing to cardiac stress

The reduced LVEF should be worked up as a separate cardiovascular problem, not attributed to B12 deficiency based on current evidence.