Vitamin B12
Understanding Vitamin B12
Its role, importance, and what blood levels mean for your health and longevity
TL;DR
- Vitamin B12 (cobalamin) is vital for brain function, red blood cell formation, and DNA synthesis.
- Both low and high blood B12 levels are linked to higher risk of death from all causes.
- The lowest mortality risk is seen in the middle range, roughly 200–400 pmol/L.
- Very high B12 may indicate hidden disease, while low B12 directly causes nerve and blood problems.
- Checking vitamin B12 and related markers (MMA, homocysteine) gives a better picture than B12 alone.
What Vitamin B12 Is and Why It Matters
Vitamin B12 is an essential nutrient the body cannot produce on its own.
It supports three key functions:
- Formation of healthy red blood cells and prevention of anaemia
- Maintenance of brain and nerve function
- DNA synthesis and cell repair
The body absorbs B12 through food (animal products like fish, meat, eggs, and dairy) or supplements.
Deficiency can develop slowly, especially in people who eat little animal food, have digestive issues, or use certain medications (such as metformin or acid blockers).
How Vitamin B12 Is Made and Measured
Most people get B12 from diet, but it is also stored in the liver and recycled in the body.
Blood tests measure total serum B12, expressed in picomoles per litre (pmol/L).
Normal lab reference ranges are about 140–700 pmol/L, but optimal health is often observed around 200–400 pmol/L.
| Source | Contribution | Notes |
|---|---|---|
| Diet (animal foods, fortified products) | 100–400 µg/day | Absorbed via intrinsic factor in stomach |
| Body storage | 2–5 mg total | Mostly in the liver |
| Elimination | Slow | Body reuses B12 efficiently; deficiency takes years to develop |
The Relationship Between B12 and Longevity
Large population studies show a U-shaped relationship between vitamin B12 and all-cause mortality:
both low and high serum B12 levels are linked with shorter life expectancy.
| Serum B12 (pmol/L) | Serum B12 (pg/mL) | Mortality risk summary | Typical cause or context |
|---|---|---|---|
| <200 | <271 | Deficiency; higher stroke and vascular risk | Poor intake or absorption |
| 200–400 | 271–542 | Lowest mortality risk | Optimal physiological range |
| 400–600 | 542–813 | Moderately increased all-cause mortality risk | Often benign; monitor trends |
| >600 | >813 | Significantly increased all-cause mortality risk | May signal hidden disease or inflammation |
Why Both Low and High B12 Are Problematic
Low B12 causes direct harm through:
- Anaemia and fatigue
- Memory loss and neuropathy
- Elevated homocysteine and vascular risk
- Increased frailty and cognitive decline in older adults
High B12, on the other hand, usually reflects:
- Liver disease (reduced clearance)
- Cancer (cell turnover releasing B12 into blood)
- Chronic inflammation or infection
- Certain blood disorders
High B12 from diet or supplements is not shown to cause harm. It usually becomes concerning only when unexplained or accompanied by illness.
Functional Markers for Better Accuracy
Serum B12 alone may not show the full picture.
Functional markers help identify whether B12 in the blood is actually working inside cells.
| Marker | What It Measures | Why It Matters |
|---|---|---|
| Methylmalonic acid (MMA) | Metabolic function of B12 | Elevated when B12 is insufficient |
| Homocysteine | Amino acid metabolism | High levels suggest B12 or folate deficiency |
| Holotranscobalamin (holoTC) | Active B12 fraction | More reliable early marker of deficiency |
Elevated MMA or homocysteine predict higher all-cause and cardiovascular mortality, even when serum B12 looks normal.
Key Insights
- Both low and high B12 levels are linked to higher mortality risk.
- High B12 usually signals disease, not over-supplementation.
- The safest zone for longevity appears around 200–400 pmol/L.
- Functional tests (MMA, homocysteine) add valuable insight.
- B12 supplementation is safe, affordable, and effective for deficiency.
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Disclaimer: This content is for educational purposes only and is not a substitute for medical advice.
Scientific summaries were prepared using peer-reviewed research and the AI models platform.