What happens when your vitamin B is low?: Symptoms, Risks, and Solutions

October 25, 2025 •

3 min read

With up to 20% of adults over 60 in the United States and United Kingdom potentially deficient in vitamin B12, understanding what happens when your vitamin B is low is increasingly important for recognizing signs and preventing serious health complications.

Quick Summary

Low vitamin B levels can cause fatigue, nerve damage, and cognitive issues, potentially leading to anemia and mental health problems. The effects vary depending on which B vitamins are lacking and the duration of the deficiency.

Key Points

Neurological Symptoms: B vitamin deficiencies, especially B12, frequently cause nerve issues like tingling, numbness, and balance problems.
Anemia is Common: A lack of B12 or folate impairs red blood cell production, leading to anemia, which causes fatigue, weakness, and paleness.
Diverse Causes: Deficiencies can result from dietary choices (like veganism), poor absorption due to medical conditions (Crohn's, gastritis), medications (metformin), or natural aging.
Serious Risks: Left untreated, low B vitamins can lead to severe complications, including irreversible nerve damage, heart failure, and cognitive decline.
Diagnosis and Treatment: A healthcare provider can diagnose a deficiency with blood tests and prescribe appropriate treatment, such as injections, oral supplements, or dietary changes.
Mental Health Link: Low B vitamins are linked to psychological issues like depression, anxiety, confusion, and memory loss, due to their role in neurotransmitter synthesis.
Folate vs. B12: While both cause megaloblastic anemia, only B12 deficiency results in elevated methylmalonic acid (MMA) and causes long-term neurological damage.

The B-complex vitamins, an essential group of eight water-soluble vitamins, are vital for cellular metabolism. Unlike fat-soluble vitamins, most B vitamins are not significantly stored in the body and require regular intake through diet, except for B12 which can be stored in the liver. Deficiencies can arise from insufficient diet, malabsorption, medications, or increased needs. When B vitamin levels are low, health impacts can range from mild symptoms to severe damage.

Common Signs of a B Vitamin Deficiency

A deficiency in B vitamins can cause a variety of symptoms that often develop slowly. While specific signs depend on the lacking vitamin, common indicators include fatigue and weakness, often linked to anemia.

Common signs include:

Fatigue and Weakness: A frequent early symptom, often due to megaloblastic anemia caused by B12 or folate deficiency.
Neurological Symptoms: Numbness or tingling, particularly in the hands and feet, can signal B12 deficiency, impacting nerve function.
Skin Changes: Pale or yellowish skin may occur due to anemia and the breakdown of red blood cells.
Cognitive and Psychological Changes: Low B vitamins can affect mood and cognition, leading to depression, anxiety, confusion, or memory issues.
Oral Issues: A swollen, red tongue (glossitis), mouth sores, or a burning sensation can be symptoms.
Gastrointestinal Problems: Symptoms like nausea, appetite loss, weight loss, and diarrhea are possible.
Cardiovascular Issues: To compensate for reduced oxygen, the heart may beat faster, leading to palpitations or shortness of breath.

Causes of Low B Vitamin Levels

Low B vitamin levels can be caused by various factors, including diet, medical conditions, and medications.

Diet: Vegan and vegetarian diets increase the risk of B12 deficiency due to limited animal product intake. Insufficient intake of fruits, vegetables, and whole grains can lead to folate deficiency.
Malabsorption: Conditions like Crohn's disease, celiac disease, and atrophic gastritis can impair B vitamin absorption.
Pernicious Anemia: An autoimmune condition that interferes with B12 absorption, particularly common in older adults.
Medications: Certain drugs, including those for acid reflux and diabetes, can affect B12 absorption.
Age: B12 absorption may decrease with age, increasing risk for older adults.
Alcohol: Excessive alcohol consumption can damage the digestive system and hinder B vitamin absorption and storage.
Increased Needs: Pregnancy increases the requirement for folate to prevent neural tube defects.

Comparison of Key B Vitamin Deficiencies

Deficiencies in B12 and B9 (folate) are particularly notable for their effects on blood and nerve health. While both can cause megaloblastic anemia, their other characteristics differ.


Feature	Vitamin B12 (Cobalamin) Deficiency	Vitamin B9 (Folate) Deficiency
Primary Cause	Malabsorption, inadequate intake, gastric issues.	Poor diet, alcoholism, medications.
Neurological Symptoms	Present; can be irreversible if untreated.	Absent.
Methylmalonic Acid (MMA) Levels	Elevated.	Normal.
Homocysteine Levels	Elevated.	Elevated.
Liver Storage	Stores last for years.	Stores deplete in months.
Megaloblastic Anemia	Can cause macrocytic, megaloblastic anemia.	Can cause macrocytic, megaloblastic anemia, similar to B12.

Diagnosis and Treatment

Early diagnosis is vital. A healthcare provider will perform an exam and order tests if a deficiency is suspected.

Diagnosis

Blood Tests: Measure B12 and folate levels and may check markers like MMA and homocysteine.
Other Tests: For B12 deficiency, tests may identify the cause, such as checking for pernicious anemia antibodies.

Treatment

Supplements: Treatment may involve oral supplements, nasal sprays, or injections. Injections are often used for severe cases or absorption problems.
Dietary Changes: Increasing intake of B-rich foods can help manage deficiencies. Vegans may require consistent supplementation.
Addressing the Cause: Treating the underlying cause, whether medical or medication-related, is crucial for long-term management.

Conclusion: Prioritizing Your B Vitamin Intake

Failing to address a vitamin B deficiency can result in significant health issues affecting the nervous, cardiovascular, and mental systems. While a balanced diet is fundamental, certain individuals, such as older adults, pregnant women, and those with specific medical conditions or dietary restrictions, are at higher risk and may need monitoring. Prompt identification and treatment through supplements or diet can often reverse symptoms and prevent serious, lasting complications. Consulting a healthcare professional for diagnosis and treatment is highly recommended.

For more information on the wide-ranging effects and management of vitamin B12 deficiency, visit this comprehensive guide on Healthline.

Frequently Asked Questions

Early signs of a B vitamin deficiency often include fatigue, lethargy, pins and needles (paraesthesia), headaches, a sore and red tongue, or mood changes like irritability or depression.

Yes, a vitamin B12 deficiency can directly impact your mood and mental health, potentially leading to depression, anxiety, confusion, and other neuropsychiatric symptoms due to its role in crucial neurological functions.

Treatment for B12 deficiency often starts with injections of hydroxocobalamin, especially for severe cases or malabsorption issues. Follow-up treatment may involve ongoing injections or oral supplements, depending on the underlying cause.

Vitamin B12 is found primarily in animal products such as meat, fish, eggs, and dairy. Vegan and vegetarian sources include fortified cereals, plant-based milks, and nutritional yeast.

If left untreated, a severe deficiency can lead to irreversible nerve damage (neuropathy), cognitive impairment, vision problems, heart conditions, and fertility issues.

Yes, individuals following a strict vegan or vegetarian diet are at a higher risk of B12 deficiency because this vitamin is mainly found in animal products. Regular intake of fortified foods or supplements is recommended.

Both can cause anemia, but B12 deficiency is distinguished by specific neurological symptoms and elevated levels of methylmalonic acid (MMA), while folate deficiency does not cause neurological damage and has normal MMA levels.

Those at highest risk include older adults, people with digestive disorders like Crohn's disease, individuals with autoimmune conditions like pernicious anemia, and people on restricted diets such as veganism.