What Happens if I Lack Vitamin B?

December 4, 2025 •

4 min read

An estimated 1-5% of the general population has a vitamin B12 deficiency, with rates climbing higher among older adults and individuals with certain health conditions. A deficiency in any of the eight B vitamins can cause a wide array of problems, affecting everything from energy levels and neurological function to red blood cell production.

Quick Summary

A deficiency in one or more B vitamins can lead to a variety of physical, neurological, and psychological symptoms, with severity dependent on the specific vitamin involved. Common issues include fatigue, anemia, and nervous system dysfunction. Diagnosis requires medical testing, and treatment often involves dietary changes, supplements, or injections to restore healthy levels.

Key Points

Neurological damage: Untreated vitamin B12 deficiency can cause nerve damage, leading to numbness, tingling, difficulty walking, and vision problems.
Megaloblastic anemia: Deficiencies in vitamins B12 and B9 (folate) can cause a type of anemia where red blood cells are abnormally large and function poorly, leading to fatigue and paleness.
Psychological symptoms: Low B vitamin levels are associated with mood changes, irritability, and in severe cases, cognitive decline and dementia.
Pregnancy risks: A lack of folate during pregnancy increases the risk of neural tube defects in the developing fetus, which affect the brain and spinal cord.
Gradual onset: Symptoms of B vitamin deficiencies often develop slowly over time, making them difficult to diagnose without medical testing.
Varied causes: Deficiencies can result from poor diet, malabsorption due to medical conditions, autoimmune diseases like pernicious anemia, or certain medications.
Treatment depends on severity: Mild cases may respond to dietary changes and oral supplements, while severe deficiencies often require regular injections to correct.

The Diverse Roles of B Vitamins

B vitamins are a complex of eight water-soluble nutrients, each playing a critical and distinct role in the body's metabolism and overall health. Unlike fat-soluble vitamins, they are not stored in large quantities and must be replenished regularly through diet or supplementation. Collectively, they are vital for converting food into energy, synthesizing red blood cells, and maintaining proper nerve function. A deficiency in any one of them can disrupt these essential processes, leading to noticeable and potentially serious health consequences.

Consequences of Specific B Vitamin Deficiencies

While a general lack of B vitamins can cause systemic issues, specific deficiencies have unique effects. A deficit in vitamin B12 (cobalamin) and B9 (folate) are among the most common and widely studied.

Vitamin B12 (Cobalamin) Deficiency

Neurological problems: Untreated B12 deficiency can damage the nervous system, leading to numbness, tingling (paraesthesia) in the hands and feet, vision problems, and difficulty with balance and coordination. In severe cases, it can cause peripheral neuropathy, spinal cord degeneration, and even paralysis.
Psychological symptoms: Mood changes, such as irritability and depression, are common. More severe cases may involve confusion, memory loss, dementia, paranoia, and delusions.
Megaloblastic anemia: B12 is essential for producing healthy red blood cells. A deficiency causes the bone marrow to produce abnormally large, immature, and poorly functioning red blood cells, leading to fatigue, weakness, and a pale or yellowish tinge to the skin.

Vitamin B9 (Folate) Deficiency

Megaloblastic anemia: Like B12 deficiency, low folate can cause megaloblastic anemia, resulting in extreme tiredness, weakness, and a sore tongue.
Birth defects: Folate is critical for fetal development. A deficiency during pregnancy significantly increases the risk of serious birth defects affecting the brain and spinal cord, known as neural tube defects, such as spina bifida.
Cardiovascular and cancer risk: Research suggests that low folate levels may increase the risk of cardiovascular disease and certain cancers, including colon cancer.

Other B Vitamin Deficiencies

Thiamine (B1) deficiency: Rare in developed countries but can occur with chronic alcoholism. Severe deficiency can lead to Wernicke-Korsakoff syndrome, which affects the nervous system and causes altered mental status and memory loss.
Riboflavin (B2) deficiency: Also rare, this can result in skin rashes, cracks at the corners of the mouth (cheilosis), and vision problems.
Niacin (B3) deficiency: Severe lack of niacin causes pellagra, characterized by dermatitis, diarrhea, and dementia.
Pyridoxine (B6) deficiency: Can lead to anemia, depression, confusion, and a weakened immune system.

Symptoms of a B Vitamin Deficiency

Symptoms often develop gradually and can be non-specific, making them easy to overlook. Common signs include:

Extreme fatigue and weakness
Numbness or tingling in the hands and feet (pins and needles)
A sore, red, and swollen tongue (glossitis) and mouth ulcers
Changes in mood, such as irritability and depression
Difficulty with memory, confusion, and trouble concentrating
Problems with vision
Digestive issues, like nausea, vomiting, or diarrhea
Shortness of breath and heart palpitations, particularly with B12 or folate deficiency anemia

Diagnosis and Treatment Options

Diagnosing a B vitamin deficiency begins with a medical history and physical exam, followed by blood tests. Blood tests can measure levels of specific B vitamins, as well as markers like methylmalonic acid and homocysteine, which rise with low B12.

Comparison of Treatment Methods


Method	Best for	Pros	Cons
Dietary Changes	Mild deficiencies; long-term prevention	Natural, addresses root cause (if dietary); improves overall health.	Can be slow to reverse deficiency; may not be enough for malabsorption issues.
Oral Supplements	Moderate deficiencies; dietary gaps	Readily available; high-dose options for better absorption.	Some absorption issues persist; requires consistent intake.
Injections	Severe deficiencies; malabsorption	Most effective for rapid and complete absorption; bypasses digestive issues.	Requires regular doctor visits or self-administration; potentially lifelong treatment.

For dietary deficiencies, increasing intake of foods rich in B vitamins is the primary strategy. Excellent sources include liver, meat, eggs, fish (such as salmon and trout), dairy products, legumes, leafy greens, nuts, and fortified cereals. Individuals on a strict vegan diet, for instance, need to pay close attention to B12 intake, often through fortified foods or supplements, as it is only naturally found in animal products.

Conclusion

Lacking vitamin B can have serious and wide-ranging effects on your body, impacting your physical energy, mental clarity, and nervous system function. Recognizing the diverse symptoms and understanding your risk factors—such as diet, age, or underlying health conditions—is the first step toward prevention and treatment. While mild cases may be managed through dietary changes and oral supplements, severe deficiencies, particularly B12, often require medical intervention like injections. Early detection is crucial, as some nerve damage can be permanent if left untreated. If you suspect a deficiency, consulting a healthcare professional for a proper diagnosis and treatment plan is essential.

Visit the NIH Office of Dietary Supplements for reliable information on Vitamin B12.

Frequently Asked Questions

The most common symptom across many B vitamin deficiencies is fatigue or a lack of energy, which can stem from anemia or poor cell metabolism.

Yes, vitamin B12 is found almost exclusively in animal products, so individuals on a strict vegan diet are at a higher risk of developing a deficiency if they do not consume fortified foods or take supplements.

A healthcare provider will diagnose a deficiency through a physical examination and blood tests that measure the levels of specific B vitamins or metabolic byproducts, like methylmalonic acid.

B vitamins are water-soluble, and excess amounts are typically excreted through urine, making toxicity rare. However, it is always best to consult a healthcare provider for the correct dosage, especially with high-dose supplements.

Yes, a deficiency, particularly in vitamin B12, can cause significant nerve damage (neuropathy) that may result in permanent symptoms like numbness, tingling, and coordination issues if left untreated.

Yes, treating a B12 deficiency with folic acid alone can correct the anemia symptoms while allowing the neurological damage to progress undetected. That is why it's crucial to test B12 levels before treating a folate deficiency.

Many foods are excellent sources of B vitamins, including organ meats (liver), salmon, beef, eggs, dairy, leafy greens, legumes, and fortified cereals.