Complete Testing & Optimization Guide
Optimal ranges, provider comparison, and strategies to improve your Vitamin B12 levels
Included in 6 of 10 major testing providers
Vitamins &Nutrients
neuropathy
Abnormal Vitamin B12 levels can indicate underlying health issues that may go undetected without proper testing. Regular monitoring helps catch problems early when they're most treatable.
Understanding your Vitamin B12 levels enables targeted interventions, tracks treatment effectiveness, and helps optimize your overall health and performance.
Vitamin B12 (cobalamin) is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, neurological function, and the methylation cycle. Unlike most vitamins, B12 is found almost exclusively in animal products (meat, fish, eggs, dairy), making vegetarians and vegans particularly susceptible to deficiency. B12 is absorbed in the small intestine with the help of intrinsic factor (a protein produced by stomach parietal cells), and deficiency can result from either dietary insufficiency or malabsorption.
Here's the critical insight:B12 deficiency is insidious and often misdiagnosed. It can take 5-10 years to develop after B12 intake stops, because the liver stores 2-5 mg (enough for 3-5 years). Early symptoms—fatigue, brain fog, mood changes—are nonspecific and often attributed to aging or stress. But if left untreated, B12 deficiency causes irreversible neurological damage:peripheral neuropathy, cognitive decline, dementia, and spinal cord degeneration (subacute combined degeneration). Standard reference ranges (>200 pg/mL) are too low;functional medicine practitioners target >400-500 pg/mL to prevent subclinical deficiency.
Serum B12 measures total B12 in blood, but it's not always reliable. Some people have normal serum B12 but functional deficiency at the cellular level. Methylmalonic acid (MMA) and homocysteine are more sensitive functional markers:they rise when B12 is insufficient for cellular metabolism. If serum B12 is borderline (200-400 pg/mL) and you have symptoms, check MMA and homocysteine to confirm deficiency.
Bottom line: TSH and Free T4 alone miss people with conversion problems. Free T3 is the only way to know if you have enough active thyroid hormone at the tissue level.
| Range Type | Level | Clinical Significance |
|---|---|---|
| Optimal (Longevity) | 500-1000 pg/mL | Target range for optimal brain health, energy, and methylation. Many functional medicine doctors target >600 pg/mL. |
| Adequate (Standard) | 400-500 pg/mL | Meets standard guidelines but may be suboptimal for some individuals, especially if symptoms present. |
| Suboptimal | 200-400 pg/mL | Low-normal range. May have subclinical deficiency with elevated MMA/homocysteine. Consider supplementation if symptomatic. |
| Deficient | <200 pg/mL | Frank deficiency. High risk of anemia, neuropathy, cognitive impairment. Requires immediate B12 replacement (sublingual or injection). |
Standard lab range:neuropathy
>1000 pg/mL
B12 Supplementation (Dose and Form)
Identify and Treat Underlying Cause
Optimize Methylation Cofactors
Address Elevated Homocysteine (if >10 mcmol/L)
Note: Check MMA if Borderline B12
Note: Fatigue, weakness, low energy|Shortness of breath, palpitations (anemia)|Pale or jaundiced skin|Glossitis (sore, red, smooth tongue)|Mouth ulcers|Peripheral neuropathy:tingling, numbness in hands/feet (starts distally)|Balance problems, difficulty walking, ataxia|Memory problems, brain fog, poor concentration|Depression, mood changes, irritability|Dementia, cognitive decline (in severe chronic deficiency)|Vision problems (optic neuropathy, rare)|Subacute combined degeneration (spinal cord damage, irreversible if untreated)
Liver disease:Hepatitis, cirrhosis (impaired B12 clearance).|Kidney disease:Chronic kidney failure (reduced excretion).|Myeloproliferative disorders:Leukemia, polycythemia vera (increased B12-binding proteins).|Excessive B12 supplementation:>1000 mcg/day (generally harmless, water-soluble).
Source:Baseline:Check serum B12 if symptoms of deficiency (fatigue, neuropathy, cognitive issues) or risk factors (vegetarian/vegan, elderly, on metformin/PPIs).|If borderline (200-400 pg/mL):Check MMA and homocysteine to confirm functional deficiency.|After starting supplementation:Retest in 3 months to ensure adequate repletion. Goal >500 pg/mL.|Annual screening:For vegetarians/vegans, elderly (>60), patients on metformin or PPIs.|If treating pernicious anemia:Monitor B12 and MMA to ensure adequacy of injection schedule (may need monthly injections lifelong).|If elevated homocysteine:Retest 3 months after B12/folate/B6 supplementation to confirm normalization.
B12 deficiency affects 10-15% of adults >60 due to atrophic gastritis and reduced intrinsic factor. Vegetarians/vegans have 50-90% prevalence if not supplementing. Metformin users have 30% risk. Subclinical deficiency (B12 200-400 pg/mL with elevated MMA) is much more common.
Source:Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr. 2009;89(2):693S-696S.
B12 deficiency causes brain atrophy, cognitive decline, and dementia. Observational studies show low B12 (<300 pg/mL) associated with 2-3x higher Alzheimer's risk. B12 supplementation slows brain atrophy by 30-50% in elderly with high homocysteine and prevents progression from MCI to dementia.
Source:Smith AD, et al. Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment. PLoS One. 2010;5(9):e12244.
B12 deficiency raises homocysteine, which damages endothelium and increases CVD risk. Meta-analyses show homocysteine >10 mcmol/L associated with 50% higher CVD risk. B12/folate/B6 supplementation lowers homocysteine by 25-30% but CVD benefit in RCTs is modest (likely because started too late in disease process).
Source:Wald DS, et al. Homocysteine and cardiovascular disease:evidence on causality from a meta-analysis. BMJ. 2002;325(7374):1202.
B12 deficiency is a common cause of peripheral neuropathy (tingling, numbness, pain in hands/feet). Early treatment with B12 injections can reverse neuropathy, but delayed treatment may result in permanent nerve damage. Methylcobalamin form may be superior to cyanocobalamin for neurological issues.
Source:Healton EB, et al. Neurologic aspects of cobalamin deficiency. Medicine. 1991;70(4):229-245.
| Provider | Includes Test | Annual Cost | Total Biomarkers |
|---|---|---|---|
 Superpower | ✓ | $199 | 100+ |
 WHOOP Advanced Labs | — | $349 | 65 |
 Labcorp OnDemand | — | $398 | 30+ |
| — | $486 | 40+ | |
| ✓ | $468 | 83 | |
| ✓ | $798 | 100+ | |
 InsideTracker | — | $680 | 48 |
 Function Health | ✓ | $499 | 100+ |
| ✓ | $900 | 70+ | |
| ✓ | $1150 | 110 | |
| — | $Varies | 75+ |
Choose from 6 providers that include this biomarker in their panels
Vitamin B12 is a vitamins &nutrients biomarker that Vitamin essential for nerve function and red blood cells The normal reference range is neuropathy. Regular testing helps track changes and identify potential health issues early.
6 out of 10 major blood testing providers include Vitamin B12 in their standard panels. These include Superpower, Blueprint, Mito Health and others.
For most people, testing Vitamin B12 2-4 times per year is recommended to establish baseline levels and track trends. If you have abnormal results or are actively working to optimize this biomarker, more frequent testing (quarterly) may be beneficial. Always consult with your healthcare provider for personalized testing frequency recommendations.
The standard laboratory reference range for Vitamin B12 is neuropathy. However, many functional medicine practitioners recommend tighter "optimal" ranges for peak health and performance. Your ideal range may vary based on your age, sex, health goals, and other individual factors. Work with a healthcare provider familiar with optimal ranges to determine your target levels.
Most direct-to-consumer blood testing services that include Vitamin B12 provide the physician order as part of their service. However, some states have restrictions on direct-to-consumer testing. Check with your chosen provider about availability in your state and whether they provide the necessary physician authorization.
Essential for nerve health and red blood cell production. Deficiency causes anemia
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs and before making decisions about blood testing.
