You can't concentrate. You feel like you're in a fog. You're exhausted but your bloodwork is "normal." Before you accept another diagnosis of "stress" or "anxiety," consider this: vitamin B12 deficiency affects up to 15% of the population and is frequently missed by standard testing.
B12 deficiency is particularly common in women - and its symptoms often mimic depression, chronic fatigue syndrome, and early dementia.
What Does B12 Do?
Vitamin B12 (cobalamin) is essential for:
- Energy production: Helps convert food into cellular energy
- Neurological function: Maintains the myelin sheath that protects nerves
- DNA synthesis: Required for cell division and red blood cell formation
- Mood regulation: Involved in serotonin and dopamine production
- Cognitive function: Crucial for memory and mental clarity
Symptoms of B12 Deficiency
B12 deficiency symptoms often develop gradually and can be mistaken for other conditions:
- Fatigue and weakness
- Brain fog and difficulty concentrating
- Memory problems
- Depression and mood changes
- Numbness or tingling in hands and feet (paresthesia)
- Balance problems
- Pale or jaundiced skin
- Glossitis (smooth, sore tongue)
- Shortness of breath
- Heart palpitations
Warning: Neurological symptoms from B12 deficiency can become permanent if left untreated for too long. Early detection matters.
Who's at Risk?
Certain groups are at higher risk for B12 deficiency:
- Vegetarians and vegans: B12 is found almost exclusively in animal products
- Women on hormonal birth control: Oral contraceptives can deplete B12 levels
- Metformin users: This common diabetes medication reduces B12 absorption by 10-30%
- People taking PPIs or H2 blockers: Stomach acid is needed for B12 absorption
- Those with digestive conditions: Celiac disease, Crohn's, or gastric bypass surgery impair absorption
- Adults over 50: Stomach acid production decreases with age
- People with autoimmune conditions: Pernicious anemia is an autoimmune cause of B12 deficiency
Why Standard B12 Tests Miss Deficiency
Here's the problem with standard serum B12 testing: you can have symptoms of deficiency while your blood levels appear "normal."
The standard reference range for serum B12 is approximately 200-900 pg/mL. However:
- Symptoms often appear below 400-500 pg/mL
- Japan and some European countries set their "deficient" cutoff at 500 pg/mL
- Serum B12 measures total B12, not how much is actually available to cells
Better Tests for B12 Status
- Methylmalonic Acid (MMA): Elevated MMA indicates B12 deficiency at the cellular level, even when serum B12 looks normal. This is a more sensitive marker.
- Homocysteine: Elevated homocysteine can indicate B12 (or folate) deficiency and is also a cardiovascular risk marker.
- Active B12 (Holotranscobalamin): Measures the portion of B12 actually available for cells to use.
Best practice: If your serum B12 is below 500 pg/mL AND you have symptoms, consider testing MMA or starting a trial of supplementation.
The Birth Control Connection
Many women don't realize that oral contraceptives can deplete B12 levels. Research shows that women on hormonal birth control tend to have lower B12 levels than those not using it.
If you've been on birth control for years and struggle with fatigue, brain fog, or mood changes, B12 deficiency could be a contributing factor.
B12 and Mental Health
B12 deficiency is increasingly recognized as a cause of psychiatric symptoms. Studies have found low B12 in patients with:
- Depression
- Anxiety
- Psychosis
- Cognitive decline
Before accepting a mental health diagnosis, it's worth checking B12 status - especially if you have risk factors for deficiency.
Addressing B12 Deficiency
Food Sources
- Beef liver (highest source)
- Clams and shellfish
- Fish (salmon, trout, tuna)
- Beef and poultry
- Eggs and dairy
- Fortified foods (cereals, nutritional yeast, plant milks)
Supplementation
If you're deficient or at high risk, supplementation may be necessary:
- Methylcobalamin: The active, methylated form - often preferred
- Cyanocobalamin: The most common supplemental form
- Sublingual or injections: May be needed if absorption is impaired
The Bottom Line
B12 deficiency is common, underdiagnosed, and can cause symptoms that significantly impact your quality of life. If you're dealing with unexplained fatigue, brain fog, or neurological symptoms, don't assume it's just stress.
Test your levels - and look at optimal ranges, not just whether you're technically "in range." Catching and correcting B12 deficiency can be truly life-changing.
Get answers, not guesses. Get your B12 tested with EllaDx's comprehensive nutrient panel.
Sources
- Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr. 2009.
- de Jager J, et al. Long term treatment with metformin and risk of vitamin B-12 deficiency. JAMA Intern Med. 2010.
- Shere M, et al. Association between use of oral contraceptives and folate status. J Obstet Gynaecol Can. 2015.
- Sangle P, et al. Vitamin B12 supplementation: Preventing onset and improving prognosis of depression. Cureus. 2020.