What is caused by inadequate vitamin B12 intake? The serious health consequences explained

November 14, 2025 •

2 min read

According to an analysis of NHANES data from 2007–2018, approximately 12.5% of US adults have vitamin B12 insufficiency. What is caused by inadequate vitamin B12 intake includes a wide range of issues affecting the blood, nerves, and brain, underscoring the vital role of this nutrient in overall health.

Quick Summary

An inadequate intake of vitamin B12 can cause significant health problems, from megaloblastic anemia to irreversible nerve damage and cognitive impairments if left untreated.

Key Points

Anemia and Fatigue: Inadequate B12 intake can cause megaloblastic anemia, leading to persistent fatigue, weakness, and paleness due to a lack of healthy red blood cells.
Neurological Damage: Deficiency can cause irreversible damage to the nervous system, resulting in symptoms like numbness, tingling, vision problems, and difficulty with balance.
Cognitive Impairment: Severe B12 deficiency is linked to memory loss, confusion, mood changes, and even an increased risk of dementia, particularly in older adults.
At-Risk Populations: Vegans, older adults, and individuals with gastrointestinal conditions like Crohn's or pernicious anemia are at a higher risk for deficiency.
Importance of Absorption: Even with sufficient dietary intake, impaired absorption due to autoimmune diseases or gastric surgery can lead to a severe deficiency.
Treatment is Effective: The condition is treatable with oral supplements or injections, but prompt action is essential to prevent permanent neurological damage.

Understanding the Critical Role of Vitamin B12

Vitamin B12, or cobalamin, is an essential water-soluble vitamin vital for nerve function, red blood cell formation, DNA synthesis, and metabolism. The body stores B12, primarily in the liver, which can delay the appearance of deficiency symptoms. Insufficient intake or impaired absorption depletes these stores, leading to health issues.

Causes of Inadequate B12 Levels

Inadequate Dietary Intake

A primary cause is a diet low in B12-rich foods, particularly for vegetarians and vegans as B12 is mainly found in animal products. Fortified foods and supplements are options, but inconsistent use can lead to deficiency. Infants of vegan mothers who are exclusively breastfed are also at risk.

Malabsorption Issues

Problems with absorbing B12 are the most common cause of deficiency. Causes include pernicious anemia, gastrointestinal disorders, surgery, and atrophic gastritis.

Other Risk Factors

Excessive alcohol, certain medications, and recreational nitrous oxide use can also contribute.

The Symptoms of Low Vitamin B12

Symptoms are often subtle and develop slowly. Physical symptoms include megaloblastic anemia, fatigue, weakness, pale skin, palpitations, shortness of breath, and glossitis. Neurological symptoms can include numbness, tingling, balance difficulties, memory loss, vision problems, and depression.

B12 Deficiency vs. Folate Deficiency: A Comparison

Both can cause megaloblastic anemia. However, B12 deficiency commonly presents with neurological symptoms, while folate deficiency does not. B12 deficiency leads to elevated methylmalonic acid (MMA), while folate deficiency does not.

Long-Term Complications of Untreated B12 Deficiency

Untreated deficiency can lead to severe and potentially irreversible health issues. These include permanent nerve damage, cognitive decline, cardiovascular problems, birth defects, and increased gastric cancer risk.

Prevention and Management

Prevention involves diet and supplementation. Treatment includes supplements or injections. Vegans and vegetarians should use fortified foods or supplements. A list of food sources is available from the {Link: NIH Office of Dietary Supplements fact sheet https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/}.

Conclusion

Inadequate vitamin B12 intake or absorption is a serious condition with wide-ranging health consequences, including fatigue, nerve damage, and cognitive issues. Early diagnosis and treatment are vital to prevent irreversible complications.

Frequently Asked Questions

Individuals following a strict vegan or vegetarian diet, older adults, people with autoimmune conditions like pernicious anemia, and those with gastrointestinal disorders such as Crohn's or celiac disease are at higher risk.

Early signs often include fatigue, weakness, shortness of breath, a sore and red tongue, and digestive issues like nausea or diarrhea.

Yes, a deficiency can damage the nerves, causing neurological symptoms like numbness, tingling, vision problems, and difficulty with coordination. In severe, untreated cases, this damage can be permanent.

A doctor can diagnose a deficiency with a blood test that measures your B12 levels. In some cases, additional tests, such as checking methylmalonic acid (MMA) levels, may be used.

Treatment varies based on the cause. It can involve B12 supplements (oral tablets), nasal gels, or injections for individuals with malabsorption issues.

No, B12 injections and supplements will only increase energy levels if you are already deficient. They do not have a significant effect on energy for individuals with normal B12 levels.

It is very difficult to get adequate vitamin B12 from a non-fortified plant-based diet. Vegans and vegetarians should rely on B12-fortified foods like cereals or nutritional yeast, or take supplements.