B Vitamins: Types, Benefits, and Deficiency Symptoms

What Are B Vitamins?

Hello, I am Dr. Emre Gecer. B vitamins are a group of eight water-soluble vitamins that act as coenzymes in essential biological processes such as energy production, cell division, nerve transmission, and blood formation. Because they are water-soluble, they are not stored in the body (with the exception of B12, which is stored in the liver) and must be obtained daily through the diet.

B vitamins work together to regulate metabolic processes, so a deficiency in one can also impair the function of the others. Let us now examine each of them in detail.

Vitamin B1 (Thiamine)

Function

Thiamine is a critical coenzyme in carbohydrate metabolism. It is required for the function of the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase enzyme complexes. It is also important for nerve conduction and muscle function.

Deficiency Symptoms

• Dry beriberi: Peripheral neuropathy (numbness, tingling, muscle weakness, gait disturbance)
• Wet beriberi: Heart failure, edema, shortness of breath

Sources

Whole grains, brown rice, oats, legumes, pork, hazelnuts, and sunflower seeds. Daily requirement: 1.1-1.2 mg.

Vitamin B2 (Riboflavin)

Function

Riboflavin is a component of the FAD and FMN coenzymes involved in energy metabolism. It plays a role in cellular growth, fatty acid oxidation, and the activation of other B vitamins (B6, folate, niacin).

Deficiency Symptoms

• Cracks and sores at the corners of the mouth (angular stomatitis, cheilosis)
• Redness and swelling of the tongue (glossitis)
• Dermatitis (oily, scaly rashes — particularly around the sides of the nose and between the eyebrows)
• Eye sensitivity to light (photophobia), burning, and itching
• Normocytic anemia

Sources

Milk and dairy products (the richest source), eggs, liver, almonds, spinach, and mushrooms. Daily requirement: 1.1-1.3 mg.

Vitamin B3 (Niacin / Nicotinamide)

Function

Niacin is incorporated into the NAD+ and NADP+ coenzymes and participates in more than 400 enzymatic reactions. It plays a critical role in energy metabolism, DNA repair, and cellular signaling.

Deficiency Symptoms

• Dermatitis: Symmetrical, hyperpigmented rash on sun-exposed areas (Casal's necklace)
• Diarrhea: Gastrointestinal mucosal damage
• Dementia: Confusion, hallucinations, and cognitive impairment

Sources

Chicken breast, tuna, turkey, liver, peanuts, mushrooms, and green peas. Niacin can also be synthesized from the amino acid tryptophan. Daily requirement: 14-16 mg NE (niacin equivalent).

Vitamin B5 (Pantothenic Acid)

Function

Pantothenic acid is the core building block of Coenzyme A (CoA) synthesis. CoA is indispensable in many metabolic pathways, including fatty acid synthesis and oxidation, the citric acid cycle, and acetylcholine synthesis.

Deficiency Symptoms

Because pantothenic acid is present in almost every food, deficiency is extremely rare. Symptoms observed under experimental deficiency include:

• Fatigue and lethargy
• Burning sensation in the hands and feet ("burning feet syndrome")
• Headache and irritability
• Gastrointestinal complaints

Sources

Liver, avocado, whole grains, broccoli, egg yolk, mushrooms, and chicken. Daily requirement: 5 mg.

Vitamin B6 (Pyridoxine)

Function

Pyridoxine, in its active form pyridoxal 5-phosphate (PLP), acts as a coenzyme in more than 150 enzymatic reactions. It plays a role in amino acid metabolism, neurotransmitter synthesis (serotonin, dopamine, GABA, norepinephrine), hemoglobin synthesis, glycogen breakdown, and immune function.

Deficiency Symptoms

• Peripheral neuropathy (numbness and tingling in the hands and feet)
• Microcytic sideroblastic anemia (iron-loaded)
• Dermatitis (seborrheic type)
• Glossitis and stomatitis
• Depression, irritability, and confusion
• Seizures in infants (vitamin B6-dependent seizures)

Caution: Vitamin B6 can be toxic at high doses (more than 200 mg per day over extended periods) and may cause sensory peripheral neuropathy. Dose control is important when using supplements.

Sources

Chicken, salmon, tuna, chickpeas, potatoes, bananas, avocado, and peanuts. Daily requirement: 1.3-1.7 mg.

Vitamin B7 (Biotin)

Function

Biotin serves as a cofactor for carboxylase enzymes and is involved in fatty acid synthesis, gluconeogenesis, and amino acid metabolism. It also plays a role in the regulation of gene expression.

Deficiency Symptoms

• Hair loss (alopecia)
• Brittle nails
• Scaly dermatitis around the face and on the body
• Conjunctivitis
• Neurological symptoms (depression, lethargy, paresthesia)

Biotin deficiency can occur with excessive consumption of raw egg whites — the avidin protein in egg whites binds biotin and blocks its absorption. Cooking inactivates avidin.

Important note: Biotin supplementation can interfere with certain laboratory tests (thyroid function tests, troponin, BNP) and produce inaccurate results. Biotin supplements should be discontinued at least 48 hours before blood testing.

Sources

Egg yolk, liver, salmon, avocado, almonds, sweet potato, and spinach. Daily requirement: 30 mcg.

Vitamin B9 (Folate / Folic Acid)

Function

Folate is a critical coenzyme in DNA and RNA synthesis, amino acid metabolism (methionine synthesis), and cell division. It is especially important in rapidly dividing cells (bone marrow, fetal tissues).

Deficiency Symptoms

• Megaloblastic anemia: Impaired DNA synthesis in the bone marrow prevents red blood cells from maturing, producing abnormally large (megaloblast) cells. It manifests as fatigue, pallor, shortness of breath, and palpitations.
• Glossitis and mouth sores
• Neural tube defects: Folate deficiency in early pregnancy can cause serious congenital anomalies such as spina bifida and anencephaly
• Hyperhomocysteinemia (a cardiovascular risk factor)

Pregnancy and folate: All women of childbearing age are advised to take 400 mcg of folic acid daily, ideally starting at least one month before conception and continuing throughout the first trimester. Women who have previously had a child with a neural tube defect should increase the dose to 4 mg per day.

Sources

Dark leafy green vegetables (spinach, chard, arugula), legumes (lentils, chickpeas), liver, oranges, avocado, and fortified grains. Daily requirement: 400 mcg DFE (dietary folate equivalent).

Vitamin B12 (Cobalamin)

Function

B12 plays a role in DNA synthesis, methionine synthesis, and fatty acid metabolism. It is essential for myelination (formation of the nerve sheath) and red blood cell production. B12 is found naturally only in foods of animal origin, and its absorption requires the intrinsic factor protein produced in the stomach.

Deficiency Symptoms

• Megaloblastic anemia: Similar to that seen in folate deficiency (impaired DNA synthesis); macrocytic red cells and hypersegmented neutrophils

• Peripheral neuropathy (numbness and tingling in the hands and feet)
• Balance and gait disorder (ataxia)
• Loss of position and vibration sense
• Muscle weakness and spasticity

Critical warning: In B12 deficiency, giving folate alone corrects the anemia but does not prevent the progression of neurological damage. For this reason, B12 levels must always be evaluated in the treatment of megaloblastic anemia.

Causes of Deficiency

• Pernicious anemia: Intrinsic factor deficiency due to autoimmune gastritis (the most common cause in older adults)
• Vegan and vegetarian diets: Risk of deficiency is high in individuals who do not consume animal products
• Gastric surgery: Following gastrectomy or bariatric surgery
• Malabsorption: Celiac disease, Crohn's disease, chronic pancreatitis
• Medications: Long-term use of metformin, proton pump inhibitors, and H2 blockers can reduce absorption
• Aging: Gastric acid and intrinsic factor production decline

Sources

Liver, red meat, fish (salmon, tuna, sardines), milk, eggs, and cheese. Supplementation is mandatory for vegans. Daily requirement: 2.4 mcg.

Who Needs B Vitamin Supplementation?

• Vegans and vegetarians: B12 supplementation is mandatory; intake of B2, B3, and B6 may also be inadequate
• Pregnant and breastfeeding women: Folate and B12 requirements are increased
• Adults over 65: B12 absorption declines; regular oral or parenteral supplementation may be needed
• Chronic alcohol use: The risk of thiamine (B1) deficiency is particularly high
• Malabsorption syndromes: Celiac disease, Crohn's disease, short bowel syndrome
• Patients who have had bariatric surgery: All B vitamins may become deficient
• Chronic kidney disease and dialysis patients
• Patients on certain medications: Metformin (B12), phenytoin and methotrexate (folate), isoniazid (B6)

B Vitamin Supplementation: When and How?

Because B vitamins are water-soluble, excess intake is generally excreted in the urine and the risk of toxicity is low (with the exception of B6 and niacin). Even so, it is advisable to check blood levels and confirm a deficiency before starting supplementation.

• B12 supplementation: Oral (1,000-2,000 mcg per day) or intramuscular injection (preferred in pernicious anemia)
• Folate supplementation: Oral folic acid 400 mcg-5 mg per day (depending on the indication)
• B complex: Suitable for groups at general risk of deficiency (older adults, people with chronic alcohol use, patients with malabsorption)

Conclusion

B vitamins are essential nutrients required for our body to function properly. A balanced and varied diet generally meets the needs for all B vitamins. However, deficiencies can develop in the presence of risk factors such as a vegan diet, advanced age, pregnancy, chronic alcohol use, or malabsorption. Early diagnosis and appropriate treatment can prevent serious complications (megaloblastic anemia, neuropathy, neural tube defects, Wernicke-Korsakoff syndrome). If you suspect any deficiency, consult your doctor.

Wishing you good health.
Dr. Emre Gecer

References

• Harrison's Principles of Internal Medicine, 22nd Edition — Chapter: Vitamin and Trace Mineral Deficiency
• Dietary Guidelines for Americans, 2020-2025
• Green R, et al. Vitamin B12 deficiency. Nature Reviews Disease Primers. 2017;3:17040
• WHO — Guideline: Optimal Serum and Red Blood Cell Folate Concentrations