B vitamins are small, water-soluble molecules but enormous in clinical importance — addressing everything from fatigue and neuropathy to cognitive complaints and malabsorption. A clear, practical review published in The Permanente Journal pulls together the biochemistry, deficiency syndromes, at-risk groups, testing caveats, and evidence-informed clinical uses for the eight-member B-complex.
Why this matters up front:
- B vitamins are not stored in meaningful amounts; daily intake or regular repletion matters. Deficiency produces reversible — and sometimes irreversible — neurologic, hematologic, and metabolic problems.
- The review emphasizes that many presentations in primary care (fatigue, cognitive change, peripheral neuropathy, anemia, unexplained GI symptoms) can be linked to one or more B-vitamin shortfalls.
Key Clinical Points by Vitamin
Thiamine (B1)
Central to the citric acid cycle and neuronal energy. Classic severe deficiency gives Wernicke-Korsakoff and beriberi; alcoholism, malnutrition, bariatric surgery, and refeeding are major risks. The review stresses emergent parenteral repletion for Wernicke’s (Royal College and EFNS guidance cited).
Riboflavin (B2)
Important for redox reactions and synthesis of other B vitamins. Deficiency causes cheilosis, stomatitis, dermatitis and can worsen migraines; riboflavin (400 mg/day) has level-B evidence for migraine prophylaxis.
Niacin (B3)
Deficiency → pellagra (the 3 Ds: dermatitis, diarrhea, dementia). High-dose niacin has metabolic effects but carries toxicity risk (liver, hyperglycemia) above therapeutic thresholds.
Pantothenic acid (B5)
Ubiquitous in food; deficiency is rare. Some small studies suggest roles in wound healing, triglyceride lowering, and inflammatory modulation.
Pyridoxine (B6)
Central for neurotransmitter synthesis and homocysteine metabolism. Deficiency may cause microcytic anemia, neuropathy, and seizures in infants. Clinically useful for nausea of pregnancy and as antidote for isoniazid toxicity.
Biotin (B7)
Involved in fatty-acid/amino-acid metabolism and gene regulation. Deficiency uncommon but relevant with anticonvulsants or biotinidase deficiency; high-dose biotin interferes with many immunoassays — an important lab caveat.
Folate (B9)
Essential for nucleotide synthesis and preventing neural-tube defects. It’s essential to check B12 before folate repletion (to avoid masking cobalamin neuropathy) and the value of considering 5‑MTHF in MTHFR polymorphisms.
Cobalamin (B12)
Required for myelin, RBC production, and methylation. Absorption is complex (intrinsic factor, ileal uptake); consider 5‑MTHF in MTHFR polymorphisms; older adults, gastric surgery, long-term PPI/metformin users, and vegans are at risk.
Testing and Interpretation — Practical Cautions
Serum levels can be misleading. Many B vitamins require functional or cellular assays for reliable assessment; for example, erythrocyte transketolase for thiamine, erythrocyte glutathione reductase for riboflavin, methylmalonic acid and homocysteine for B12/folate, erythrocyte folate for long-term folate status. Also, biotin interference is clinically significant with streptavidin-based immunoassays (troponin, thyroid, vitamin D), so be sure to ask about supplements before ordering tests.
Who to Screen or Treat Empirically
- Populations at higher risk: chronic alcohol dependence; older adults with decreased intake/absorption; bariatric surgery patients; inflammatory bowel disease or other malabsorptive states; strict vegans; chronic PPI or metformin users; people on certain medications (e.g., isoniazid, anticonvulsants).
- The review supports targeted screening and low threshold for empiric repletion in high-risk clinical scenarios (e.g., empiric thiamine in alcohol withdrawal or suspected Wernicke’s; vitamin B12 in symptomatic deficiency or malabsorption; pyridoxine for INH toxicity).
Practical Takeaways
- Some B vitamins have specific, evidence-based clinical roles: riboflavin for migraine prophylaxis (level B), folate in pregnancy to prevent neural-tube defects, pyridoxine for nausea of pregnancy, and pyridoxine as an antidote for INH toxicity (Table 4, pages 7–9).
- The authors note that although B vitamins are generally safe at usual supplement or fortified-food levels, toxicity can occur (notably high-dose niacin and pyridoxine), so dosing should be intentional and monitored.
- Integrate dietary review, medication list, and risk factors when assessing fatigue, neuropathy, anemia, or cognitive complaints.
- Use functional biomarkers (MMA, homocysteine, erythrocyte assays) when available rather than relying solely on serum concentrations.
- Remember lab interference (biotin) and drug–nutrient interactions (isoniazid → B6 depletion; metformin → B12 malabsorption; anticonvulsants → biotin/B6 effects).
- When deficiency is suspected and risk is high, early repletion is often low-risk and can prevent permanent damage (especially with thiamine and cobalamin).
The bottom line? B vitamins are clinically consequential, often under-assessed, and frequently reversible causes of significant symptoms. The review by Hanna et al. provides a concise, clinically oriented roadmap for practitioners.
→ Download the Full Text HERE.
Reference
Hanna M, Jaqua E, Nguyen V, Clay J. B Vitamins: Functions and Uses in Medicine. Perm J. 2022 Jun 29;26(2):89-97. doi: 10.7812/TPP/21.204. Epub 2022 Jun 17. PMID: 35933667; PMCID: PMC9662251.
