What Happens to Your Body When You Have Low Vitamin B?

October 28, 2025 •

3 min read

According to the National Institutes of Health, vitamin B12 deficiency can take years to show symptoms because the body stores it in the liver. However, once deficiencies occur, a cascade of health problems can follow, impacting everything from energy levels and mood to the nervous system and red blood cell production, demonstrating what happens to your body when you have low vitamin B.

Quick Summary

A deficiency in one or more B vitamins can lead to a wide range of physical, neurological, and psychological issues. The symptoms vary depending on the specific vitamin lacking, from extreme fatigue and anemia to cognitive difficulties and nerve damage. Addressing the deficiency through diet or supplements is crucial to prevent long-term complications.

Key Points

Diverse Symptoms: What happens to your body when you have low vitamin B can vary widely, including fatigue, nerve issues, mood changes, and skin problems, depending on which specific B vitamin is deficient.
Impacts Nervous System: Deficiencies, especially in vitamin B12, can cause serious neurological problems, from tingling and numbness to memory loss and confusion.
Leads to Anemia: Low levels of B12 and folate can result in megaloblastic anemia, which causes fatigue, weakness, and shortness of breath.
Common Risk Factors: People on vegan diets, older adults, and those with gastrointestinal conditions or a history of stomach surgery are at higher risk for vitamin B deficiency.
Treatable Condition: Most vitamin B deficiencies can be managed with diet changes, oral supplements, or injections, particularly in cases of B12 malabsorption.

The Essential Role of B Vitamins

The B vitamins are a group of eight water-soluble nutrients crucial for various cellular functions. They are necessary for converting food into energy, maintaining healthy nerves and skin, and forming red blood cells. A deficiency in any of these vitamins can disrupt the body's normal processes. Understanding what happens to your body when you have low vitamin B requires looking at both the collective and individual impacts.

The Collective Impact of Low B-Vitamins

General B-vitamin deficiency often leads to persistent fatigue and lack of energy due to their role in energy production. Mood swings, irritability, and memory issues are also common, linked to nervous system health.

Specific Effects of Individual B-Vitamin Deficiencies

Each B vitamin plays a unique role, and its deficiency results in specific symptoms:

Vitamin B1 (Thiamin) Deficiency

Thiamin is essential for nerve and muscle function. Deficiency can cause beriberi, affecting the nervous and cardiovascular systems. Symptoms include nerve damage, tingling, numbness, muscle weakness, weight loss, poor appetite, and memory problems.

Vitamin B2 (Riboflavin) Deficiency

Riboflavin deficiency can lead to skin and oral issues. Symptoms include cracked lips, mouth ulcers, sore tongue, skin disorders, hair loss, and red, itchy eyes. Severe cases may cause vision problems or cataracts.

Vitamin B3 (Niacin) Deficiency

Severe niacin deficiency, or pellagra, is characterized by dermatitis, diarrhea, dementia, and potentially death. Symptoms include brown skin discoloration on sun-exposed areas, digestive issues, fatigue, depression, and mental confusion.

Vitamin B9 (Folate) and B12 (Cobalamin) Deficiencies

Deficiencies in folate and B12 can cause megaloblastic anemia. Anemia symptoms include extreme tiredness, lack of energy, headaches, and palpitations. B12 deficiency can also cause serious nerve damage, leading to tingling, numbness, difficulty walking, irritability, depression, and memory problems.

Causes and Risk Factors

Factors contributing to low vitamin B include:

Diet: Vegans are at risk for B12 deficiency.
Malabsorption: Conditions like celiac disease or Crohn's disease.
Surgery: Gastric bypass can affect absorption.
Medications: Some heartburn or diabetes drugs interfere with absorption.
Alcohol: Excessive intake impairs B-vitamin absorption.
Age: Older adults may have reduced B12 absorption.

Comparison of B12 Deficiency Symptoms


Symptom Category	Early Stages	Advanced Stages
Energy & Mood	Fatigue, weakness, irritability, brain fog, depression	Severe fatigue, apathy, lethargy, paranoia
Neurological	Mild numbness or tingling in hands and feet (paraesthesia)	Significant nerve damage, walking difficulties, balance problems (ataxia), memory loss, dementia
Physical	Pale skin, sore or red tongue (glossitis), mouth ulcers	Megaloblastic anemia, weight loss, heart palpitations, shortness of breath
Digestive	Nausea, vomiting, loss of appetite, diarrhea	More severe or persistent digestive upset

Diagnosis and Treatment

Diagnosis involves a blood test to measure vitamin levels. Additional testing may identify the cause. Treatment depends on the specific deficiency and severity. Options include oral supplements, especially for diet-related issues or older adults. Injections are used for severe cases or absorption problems. Lifelong injections may be needed for conditions like pernicious anemia. Dietary improvements with B-rich foods are also important.

Conclusion

Low vitamin B levels significantly impact your body, affecting physical, neurological, and psychological health. Symptoms vary from fatigue and anemia to nerve damage and cognitive decline. Individuals at risk, such as vegans, older adults, and those with certain medical conditions, should consider proactive testing and nutritional management. Prompt diagnosis and treatment can reverse many symptoms and prevent long-term damage, emphasizing the importance of addressing vitamin B deficiency for overall wellness.

Visit the NHS website for more information on vitamin B12 and folate deficiency

Frequently Asked Questions

The earliest signs of low vitamin B can include persistent fatigue, weakness, and irritability. You might also notice a sore tongue or experience changes in your mood.

A vitamin B deficiency is typically diagnosed with a simple blood test that measures the levels of B vitamins, such as B12 and folate, in your bloodstream. More detailed testing may follow to find the root cause.

Tingling and numbness, often called paresthesia, are common neurological symptoms associated with low levels of vitamin B12. It can also be caused by thiamin (B1) deficiency.

Yes, deficiencies in various B vitamins can impact mental health. Symptoms can include depression, irritability, confusion, and memory loss, particularly in cases of B12 and folate deficiency.

To increase B vitamins, incorporate foods like meat, fish, eggs, dairy products, and leafy green vegetables into your diet. For B12, fortified foods such as cereals and plant-based milks are a good option for vegans and vegetarians.

The fastest way to correct a severe vitamin B12 deficiency is through injections. For less severe cases, high-dose oral supplements can also be effective.

Yes, older adults are at a higher risk of vitamin B12 deficiency, often due to decreased stomach acid production, which makes it harder to absorb the vitamin from food.