B vitamins

Comprehensive Review of B Vitamins: Functions, Deficiencies, Food Sources, and Mental Health Impact

The B vitamin family includes eight essential water-soluble vitamins that play critical roles in energy metabolism, brain function, hormone regulation, and methylation. While they often work together synergistically, each B vitamin has unique functions and deficiency patterns.



Vitamin B1 (Thiamine)

  • Function: Supports energy production, glucose metabolism, nerve conduction, and heart function.
  • Sources: Whole grains, pork, legumes, sunflower seeds, and brown rice.
  • Deficiency Signs: Fatigue, irritability, nerve pain, poor coordination, heart failure, Wernicke-Korsakoff syndrome (in alcoholics).
  • Mental Impact: Deficiency linked to memory loss, confusion, anxiety, and depression.
  • Over-supplementation: Rarely toxic; excess is excreted in urine.
  • Interesting Fact: Thiamine deficiency can result in irreversible brain damage if not treated early in alcoholism.



Vitamin B2 (Riboflavin)

  • Function: Required for energy production in the mitochondria, antioxidant regeneration (glutathione), skin and eye health.
  • Sources: Eggs, dairy, leafy greens, almonds, liver.
  • Deficiency Signs: Cracked lips, sore throat, redness around the eyes, fatigue, inflammation of the tongue.
  • Mental Impact: Low riboflavin may contribute to migraines and oxidative stress in the brain.
  • Over-supplementation: Harmless yellow urine; otherwise well tolerated.
  • Interesting Fact: Riboflavin is light-sensitive—this is why milk is no longer sold in clear bottles.



Vitamin B3 (Niacin)

  • Function: Helps convert food into energy, supports skin health, DNA repair, and cholesterol metabolism.
  • Sources: Chicken, tuna, turkey, peanuts, mushrooms, beef liver.
  • Deficiency Signs: Pellagra (diarrhea, dermatitis, dementia), fatigue, poor appetite.
  • Mental Impact: Low niacin can cause cognitive decline and psychosis in severe deficiency.
  • Over-supplementation: Flushing (from niacin), liver damage in high doses.
  • Interesting Fact: Tryptophan (amino acid) can be converted into niacin in the body.



Vitamin B5 (Pantothenic Acid)

  • Function: Critical for coenzyme A production, which is essential in fat metabolism and hormone synthesis (including cortisol).
  • Sources: Avocados, mushrooms, sweet potatoes, chicken, whole grains.
  • Deficiency Signs: Fatigue, irritability, numbness, burning feet syndrome.
  • Mental Impact: May affect stress resilience and mood stability due to adrenal involvement.
  • Over-supplementation: Diarrhea in high doses; otherwise safe.
  • Interesting Fact: The name comes from the Greek "pantothen," meaning “from everywhere”—because it’s found in many foods.



Vitamin B6 (Pyridoxine / P5P)

  • Function: Involved in over 100 enzyme reactions; needed for neurotransmitter synthesis (serotonin, dopamine, GABA), hormone regulation, immune function.
  • Sources: Bananas, salmon, potatoes, poultry, fortified cereals.
  • Deficiency Signs: Irritability, depression, confusion, PMS, peripheral neuropathy.
  • Mental Impact: Low B6 linked to anxiety, depression, irritability, ADHD.
  • Over-supplementation: Neuropathy with chronic high doses (>200 mg/day).
  • Interesting Fact: Active form is P5P (pyridoxal-5-phosphate), which is better for people with impaired liver or genetic variants.



Vitamin B7 (Biotin)

  • Function: Supports keratin production (hair, skin, nails), carbohydrate metabolism, and gene regulation.
  • Sources: Eggs (yolk), nuts, seeds, liver, sweet potatoes.
  • Deficiency Signs: Thinning hair, brittle nails, dry skin, depression, fatigue.
  • Mental Impact: Deficiency may contribute to mood instability and fatigue.
  • Over-supplementation: Rarely harmful, but can interfere with lab tests (e.g., thyroid, troponin).
  • Interesting Fact: Raw egg whites contain avidin, which binds biotin and prevents its absorption.



Vitamin B9 (Folate / 5-MTHF)

  • Function: Essential for DNA synthesis, red blood cell formation, and methylation; crucial in pregnancy.
  • Sources: Leafy greens, lentils, asparagus, citrus fruits, fortified grains.
  • Deficiency Signs: Megaloblastic anemia, elevated homocysteine, fatigue, neural tube defects in pregnancy.
  • Mental Impact: Low folate linked to depression, cognitive decline, schizophrenia.
  • Over-supplementation: Excess folic acid (synthetic) may mask B12 deficiency and contribute to cancer risk.
  • Interesting Fact: Many people with MTHFR gene variants cannot convert folic acid into active folate efficiently—use methylfolate (5-MTHF) instead.



Vitamin B12 (Cobalamin)

  • Function: Vital for nerve health, DNA synthesis, red blood cells, and methylation.
  • Sources: Animal products only—meat, eggs, dairy, fish, liver.
  • Deficiency Signs: Fatigue, memory loss, tingling in hands/feet, glossitis, megaloblastic anemia.
  • Mental Impact: Strongly linked to cognitive decline, depression, anxiety, psychosis, brain fog.
  • Over-supplementation: Very safe even in high doses; excreted in urine.
  • Interesting Fact: Absorption requires intrinsic factor in the stomach—people with autoimmune gastritis, acid blockers, or gastric surgery are at high risk for deficiency.



Methylation and B Vitamins

Methylation is a process that affects DNA repair, detoxification, neurotransmitter balance, and inflammation regulation. B6, B9 (folate), and B12 are the most critical for this pathway. Deficiencies can result in elevated homocysteine, poor mental health, and chronic disease risk.



Final Thoughts

B vitamins are foundational to physical and mental health. Deficiency can present subtly as fatigue, mood issues, or skin problems and progress to severe neurological or psychiatric symptoms. Always look for methylated or active forms for better absorption, especially if you have MTHFR or COMT gene variants. While most B vitamins are water-soluble and excreted if in excess, high doses (especially B6) should be used with care and clinical guidance.

Learn more