Symptoms of Vitamin B Deficiencies According to Research

Medically Reviewed by Ian Nathan, MBChB, on 14th January 2026

Vitamin B deficiencies encompass a group of conditions in which the body lacks adequate amounts of one or more of the essential B vitamins. These water-soluble vitamins play vital roles in cellular energy production, nervous system function, red blood cell formation, DNA synthesis, and metabolic pathways. Because each B vitamin supports different biochemical processes, deficiencies can produce a broad range of clinical symptoms that affect multiple organ systems.

Understanding the B Vitamin Complex

The B vitamins include eight distinct compounds:

• Vitamin B1 (Thiamine)
• Vitamin B2 (Riboflavin)
• Vitamin B3 (Niacin)
• Vitamin B5 (Pantothenic Acid)
• Vitamin B6 (Pyridoxine)
• Vitamin B7 (Biotin)
• Vitamin B9 (Folate)
• Vitamin B12 (Cobalamin)

Each vitamin within this complex has distinct biochemical roles, but they often overlap in broader metabolic pathways, such as energy production and neurotransmitter synthesis. Because of this, deficiencies can manifest as both specific and overlapping symptoms across organ systems.

Common Clinical Presentations of B Vitamin Deficiency

Symptoms associated with B vitamin deficiencies vary depending on which vitamin is deficient, severity of the deficiency, and the duration of insufficiency. However, several features are common across multiple B vitamins:

• Fatigue and General Weakness: Impaired energy metabolism leads to persistent tiredness and lack of stamina.
• Neurological Symptoms: Numbness, tingling, neuropathy, memory problems, mood changes and confusion are frequently reported.
• Dermatologic Changes: Skin rashes, dryness, cracked lips, and inflammation of the mouth and tongue.
• Hematologic Changes: Anemia, characterized by low red blood cells or abnormal cell shapes, can be a key presentation of several B vitamin deficiencies.
• Mood and Cognitive Effects: Depression, irritability, anxiety, and cognitive fog are especially noted in B1, B2, B6 and B12 insufficiencies. Research also suggests associations between dietary intake of several B vitamins and the risk of depression. (PubMed: Associations of dietary vitamin B1, B2, B6, and B12 with depression risk)

Symptoms by Specific B Vitamin Deficiency

Vitamin B1 (Thiamine) Deficiency

Thiamine is essential for glucose metabolism and neuronal function. Deficiency can lead to reversible and irreversible conditions if untreated. Research confirms that severe thiamine deficiency produces neurological and cardiovascular symptoms. (PubMed: B Vitamin Deficiencies and Associated Neuropathies)

• Early Symptoms: Fatigue, irritability, poor concentration.
• Neurologic Manifestations: Peripheral neuropathy, reduced reflexes, balance issues, memory disturbances.
• Severe Presentations: Wernicke encephalopathy and Wernicke-Korsakoff syndrome — characterized by confusion, ophthalmoplegia (eye movement abnormalities), ataxia (loss of coordination), and memory impairment.
• Cardiovascular Symptoms: In “wet beriberi,” patients develop heart failure symptoms such as rapid heart rate and edema.

Vitamin B2 (Riboflavin) Deficiency

Riboflavin plays a role in energy metabolism and the activation of other vitamins. Deficiency can affect the skin, mucous membranes, and nervous system. Clinical reviews document characteristic mucocutaneous findings. (Cleveland Clinic Journal of Medicine: Skin Findings Associated with Nutritional Deficiencies)

• Cracks at the corners of the mouth (angular cheilitis).
• Inflammation of the tongue (glossitis) and mouth (stomatitis).
• Dry, scaly skin and seborrheic dermatitis.
• Sore throat and swelling of the lips.

Vitamin B3 (Niacin) Deficiency

Niacin deficiency causes the classic disease pellagra, marked by a set of symptoms commonly referred to as the “four Ds”: dermatitis, diarrhea, dementia, and eventually death if untreated. (NCBI: Micronutrient Intake and Deficiency Symptoms)

• Dermatitis — photosensitive skin rash and thickened skin in sun-exposed areas.
• Digestive symptoms — diarrhea or abdominal discomfort.
• Neuropsychiatric symptoms — confusion, memory loss, irritability.
• Severe deficiency may progress to dementia.

Vitamin B5 (Pantothenic Acid) Deficiency

Pantothenic acid deficiency is rare and often occurs alongside other micronutrient deficiencies. However, documented manifestations reflect its role in fatty acid metabolism and cellular function. (NCBI: Micronutrient Intake and Deficiency Symptoms)

• Fatigue, weakness.
• Headaches.
• Abdominal cramps and gastrointestinal discomfort.
• Paresthesia (tingling sensations), muscle cramps, and impaired coordination.

Vitamin B6 (Pyridoxine) Deficiency

Vitamin B6 is essential for amino acid metabolism, red blood cell production, and neurotransmitter synthesis. Deficiency presents with a wide spectrum of neurologic, hematologic and dermatologic symptoms. (NCBI: Micronutrient Intake and Deficiency Symptoms)

• Depression, irritability, confusion, and mood disturbances.
• Anemia due to disrupted hemoglobin formation.
• Paresthesia and sensory neuropathy.
• Seborrheic dermatitis, mouth sores, and inflammation of the tongue.

Vitamin B7 (Biotin) Deficiency

Biotin is critical for carbohydrate and fatty acid metabolism. Though deficiency is uncommon, it can occur in certain genetic disorders or with extensive antibiotic use. (PubMed: Vitamin-Responsive Disorders — Biotin, Cobalamin, Folate, B1)

• Hair loss and brittle nails.
• Skin rashes and dermatitis.
• Fatigue and neurological symptoms such as depression or lethargy.

Vitamin B9 (Folate) Deficiency

Folate is essential for DNA synthesis and cell division. Deficiency primarily affects red blood cell formation and nervous system development. (NCBI: Micronutrient Intake and Deficiency Symptoms)

• Megaloblastic anemia — characterized by large, immature red blood cells, leading to fatigue and weakness.
• Shortness of breath, pale skin, and rapid heartbeat.
• Irritability and cognitive difficulties.
• In pregnancy, folate deficiency is a well-established risk factor for neural tube defects in the developing fetus.

Vitamin B12 (Cobalamin) Deficiency

Vitamin B12 deficiency is one of the most clinically significant and can produce irreversible neurological damage if untreated. Its clinical manifestations extend across hematologic, neurologic, and psychiatric domains. (PubMed: Clinical Presentation of Cobalamin-Related Disorders)

• Megaloblastic anemia leading to fatigue, pallor, and shortness of breath.
• Tingling, numbness, or loss of sensation — especially in hands and feet.
• Balance problems and difficulty walking due to spinal cord involvement.
• Cognitive decline, memory problems, and mood disorders.
• Psychiatric symptoms such as depression and irritability.

Risk Factors for B Vitamin Deficiencies

B vitamin deficiencies are more likely to occur under certain conditions, including:

• Poor dietary intake of B vitamin-rich foods such as meat, dairy, eggs, leafy greens, and whole grains.
• Malabsorptive disorders such as celiac disease, Crohn's disease, and pancreatic insufficiency.
• Chronic alcoholism and severe malnutrition.
• Medications that interfere with absorption (e.g., metformin, proton pump inhibitors for B12 absorption).
• Increased physiological needs such as pregnancy for folate.
• Advanced age, which can impair absorption and intrinsic factor production, especially for B12.

When to Seek Medical Evaluation

Because B vitamin deficiency symptoms are often nonspecific and overlap with other conditions, persistent symptoms warrant professional evaluation. Laboratory tests — including serum levels of specific vitamins and complete blood counts — can confirm deficiencies and guide targeted treatment. Early diagnosis is especially important for preventing irreversible neurological damage, particularly with B12 deficiency.

References

1. B Vitamin Deficiencies and Associated Neuropathies — PubMed (2026)
2. Skin Findings Associated with Nutritional Deficiencies — Cleveland Clinic Journal of Medicine
3. Micronutrient Intake, Imbalances, and Interventions — NCBI Bookshelf
4. Associations of Dietary Vitamin B1, B2, B6, B12 with Depression Risk — PubMed (2021)
5. The Clinical Presentation of Cobalamin-Related Disorders — PubMed (2019)
6. Vitamin-Responsive Disorders: Cobalamin, Folate, Biotin, B1 — PubMed (2013)