Vignette 1 of 1· source #1
Vegan with paresthesias
Objective · Recognize subtle B12 deficiency.
A 35-year-old vegan for 7 years reports new paresthesias and balance issues. Hgb normal, MCV 99.
Best test?
Curriculum
Module 06 · 60 min
Water-Soluble Vitamins — B-complex & C
B12, folate, thiamine, B6 toxicity, and the persistent myth of high-dose vitamin C.
CoreClinicalAdvanced
Core topics
Lessons in this module
Learning objectives
By the end of this module you will be able to
- L01Distinguish B12 replacement strategies in pernicious anemia vs dietary deficiency.
- L02Counsel a patient about MTHFR polymorphisms without overpromising.
- L03Identify B6 dose threshold for sensory neuropathy (~200 mg/d chronic).
- L04Apply Cochrane evidence on vitamin C to a patient asking about cold prevention.
Expected takeaways
What you should walk away believing
- →Folic acid 400–800 mcg periconceptionally is one of the strongest public-health supplement wins.
- →B12 deficiency presents with macrocytic anemia AND neuropsychiatric symptoms that can precede hematologic changes.
- →Oral B12 ≥1000 mcg/d corrects most non-malabsorptive deficiencies.
- →Vitamin C does not prevent the common cold; modest duration reduction in regular users.
Lesson · Core emphasis
What this means for you
Patient summary
Folate (folic acid) before and during early pregnancy prevents serious birth defects. B12 deficiency is more common than people think, especially in vegans and older adults. Vitamin C doesn't prevent colds.
Clinician summary
Screen B12 in vegans, post-bariatric, metformin users, PPI long-term, and unexplained neuropathy. Folate in pregnancy = 400–800 mcg/d (4 mg with prior NTD). Cap B6 at <100 mg/d chronic. Thiamine before glucose in suspected Wernicke.
Advanced note
Methylfolate vs folic acid debate in MTHFR carriers lacks RCT-grade evidence for clinical outcomes beyond serum levels. Holotranscobalamin and MMA refine B12 diagnosis when serum B12 is borderline.
Evidence framework
Where this module sits on the device evidence map
Water-soluble vitamins: strong deficiency-rescue evidence; high-dose RCTs in repletion repeatedly null or harmful.
Myth-buster
Everyone with MTHFR mutations needs methylfolate.
Reality
~40% of the population has at least one MTHFR variant; routine genotyping and methylfolate switching are not supported by outcome data.
Evidence-graded claims
What the data says
A
Periconceptional folic acid prevents NTDs
MRC 1991 + global fortification programs.
F
IV vitamin C cures sepsis
CITRIS-ALI and LOVIT trials negative or harmful.
A
Chronic high-dose B6 causes sensory neuropathy
Established >200 mg/d chronic.
Objective self-check
Test the learning objectives
Score0 / 1(0 answered)
Q1L01 — Oral B12 dose for dietary deficiency?
Case vignettes
Apply it: real-world counseling scenarios
Short patient encounters that test your judgment, not your recall. Pick the most defensible response, then reveal the rationale and a sample coaching script you could actually say at the bedside.
Vignette proficiency
In progress · 0/1 submitted
Correct0/1 (0%)Pitfalls avoided0/0 (0%)Composite0
Composite weighting
Accuracy 60%Pitfalls 40%
← all pitfallsbalancedall accuracy →
Composite = 60% answer accuracy + 40% pitfalls avoided. Your weighting is saved for this module.
Order · randomized[1]
Quick check
Test yourself
Q1NTD prevention folic acid dose (no prior NTD)?
Q2Most specific B12 deficiency marker when serum B12 borderline?
Flashcards · Spaced repetition
Lock it in — review what's due
Due2Total2
FrontNew
2 in queueWernicke triad?
Click to reveal answer
Glossary
Key terms & abbreviations
- MMA
- Methylmalonic acid — sensitive marker of intracellular B12 deficiency.
- Holotranscobalamin
- Metabolically active B12 carrier — more specific than total serum B12.
Further reading
Optional deeper dive
- LOVIT — Lamontagne et al. — NEJM 2022↗
- USPSTF folic acid recommendation — USPSTF 2023↗