What causes low vitamin B12 levels?

From the Guidelines

Low vitamin B12 levels are primarily caused by inadequate dietary intake, malabsorption issues, or certain medical conditions, as outlined in the most recent guideline summary from the BMJ in 2024 1. The main causes of low vitamin B12 levels can be broken down into several key areas:

• Dietary deficiency: This occurs in people who consume little to no animal products, as B12 is mainly found in meat, fish, eggs, and dairy.
• Malabsorption problems: These often stem from conditions affecting the stomach or small intestine, such as pernicious anemia, atrophic gastritis, celiac disease, Crohn's disease, or surgical procedures like gastric bypass.
• Certain medications: Including proton pump inhibitors, metformin, and some anticonvulsants, which can interfere with B12 absorption.
• Age: Older adults produce less stomach acid needed for B12 absorption.
• Genetic disorders: Like transcobalamin II deficiency, which can prevent proper B12 transport in the bloodstream.
• Excessive alcohol consumption: Leading to poor nutrition and reduced B12 levels.

Some specific risk factors for vitamin B12 deficiency include:

• A diet low in vitamin B12, particularly in vegans or those who exclude animal products for religious beliefs
• Certain health conditions, such as atrophic gastritis, celiac disease, or autoimmune conditions like thyroid disease or type 1 diabetes
• Medications like colchicine, H2 receptor antagonists, metformin, phenobarbital, pregabalin, or primidone
• A family history of vitamin B12 deficiency or an autoimmune condition

The most effective approach to addressing low vitamin B12 levels involves identifying and treating the underlying cause, which may include oral B12 supplements, B12 injections, or addressing underlying conditions, as recommended in the guideline summary from the BMJ in 2024 1. For example, patients with vitamin B12 deficiency due to metformin use should be monitored for vitamin B12 deficiency annually, especially if they have been on metformin for more than 4 years or are at risk for vitamin B12 deficiency, as suggested in the Diabetes Care study from 2023 1. In cases of vitamin B12 deficiency with possible neurological involvement, immediate treatment with hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement, then every 2 months, is recommended, as outlined in the Obesity Reviews study from 2020 1.

From the Research

Causes of Low Vitamin B12 Levels

• Intrinsic factor deficiency, which hinders the absorption of vitamin B12, is a primary cause of low vitamin B12 levels, particularly in individuals with pernicious anemia (PA) 2
• Immune gastritis and the presence of anti-intrinsic factor and/or antiparietal cell antibodies can also contribute to low vitamin B12 levels 2
• Patient lifestyle, disease history, and medications can provide clues to the cause of B12 deficiency 3
• Certain medical conditions, such as pernicious anemia, can lead to low vitamin B12 levels due to the body's inability to absorb the vitamin 2, 3

Factors Affecting Vitamin B12 Stability

• Environmental factors such as temperature, pH, and light can affect the stability of vitamin B12 4
• The presence of interacting compounds, including oxidants, reductants, and other water-soluble vitamins, can also impact vitamin B12 stability 4
• The manufacturing process and storage of vitamin B12 products can influence their stability and quality 4

Consequences of Excessive Vitamin B12 Intake

• High doses of vitamin B12 can cause toxicity, leading to symptoms such as acne, palpitations, anxiety, and insomnia 5
• The administration of high doses of vitamin B12 should be approached with caution, and patients should be monitored for potential adverse effects 5