Scientists have discovered that having too much vitamin B12 in your blood, not too little, dramatically increases your chances of dying early.

Story Highlights

• Elevated vitamin B12 levels increase all-cause mortality risk by 4-6% for every 100 pmol/L increase in concentration
• Older adults with high B12 levels face a 25% increased risk of death, with cardiovascular mortality risk tripling
• The deadly effect occurs independent of traditional risk factors and persists across multiple populations worldwide
• Supplemental B12 appears more dangerous than dietary sources, challenging decades of nutritional wisdom

The Vitamin Paradox That’s Killing People

For decades, medical professionals operated under a simple assumption: more vitamins meant better health. This belief has crumbled under the weight of mounting evidence showing that elevated vitamin B12 concentrations kill people at alarming rates. Multiple studies across different continents now confirm that high B12 levels increase mortality risk by 25% to 41%, depending on the population studied.

The Netherlands cohort study tracked thousands of participants and found mortality rates of 65.7 per 10,000 person-years in the highest B12 quartile compared to just 33.8 in the lowest quartile. Meanwhile, Chinese researchers discovered that hypertensive adults with elevated B12 faced triple the cardiovascular death risk. These aren’t statistical flukes—they represent a fundamental misunderstanding of optimal nutrition.

ELEVATED VITAMIN B12

High vitamin B12? 🧪 Unlike deficiency, elevated B12 usually isn’t about diet or supplements. It’s often a marker of disease.

… but no consensus on whether/how to investigate!

See: https://t.co/y7y87wqlyU pic.twitter.com/PzxUbOHqOD

— William Aird (@WilliamAird4) September 15, 2025

Why Your B12 Supplement Might Be a Death Sentence

The most chilling discovery involves supplemental versus dietary B12 sources. Research indicates that B12 from supplements poses greater mortality risks than the same vitamin obtained from food sources. This finding demolishes the supplement industry’s core premise that synthetic vitamins are equivalent to natural sources. The difference could mean life or death for millions of older adults popping B12 pills daily.

Hospitalized patients with elevated B12 levels experienced 39% mortality within one year compared to 26% for those with normal levels. The adjusted hazard ratio of 1.71 means these patients faced 71% higher odds of death, independent of their underlying conditions. This association persisted even after accounting for cancer, autoimmune diseases, and other traditional risk factors.

The Concentration Threshold Where Death Risk Soars

Meta-analysis reveals that B12 concentrations above 400 pmol/L trigger significantly elevated mortality risks. The current medical reference range of 200-1000 pg/mL appears dangerously outdated, potentially encouraging lethal supplementation practices. Every 100 pmol/L increase beyond this threshold raises death risk by 4% in general populations and 6% among older adults.

The dose-response relationship proves particularly troubling because it suggests causation rather than mere correlation. Unlike deficiency states that show clear symptoms, elevated B12 operates as a silent killer, providing no warning signs while systematically damaging biological processes. The mechanism remains mysterious, but the mortality statistics are undeniable across multiple independent research groups.

Three Populations Where High B12 Proves Most Deadly

Older adults represent the highest-risk group, showing the strongest association between elevated B12 and premature death. Their aging bodies appear less capable of handling excess B12, possibly due to impaired cellular uptake or metabolism. The vitamin that was supposed to support healthy aging instead accelerates mortality in this vulnerable population.

Hospitalized patients and hypertensive individuals comprise the other high-risk categories. These groups already face compromised health status, and elevated B12 compounds their mortality risk substantially. The cardiovascular system appears particularly vulnerable, with heart disease deaths increasing threefold among hypertensive patients with high B12 levels. This pattern suggests that existing medical conditions amplify B12’s deadly effects.

Sources:

Analysis Says Excessive Vitamin B12 Concentration Can Increase Mortality Risk
Elevated plasma vitamin B12 concentrations and mortality: a population-based cohort study
Association of Baseline Serum Vitamin B12 Concentrations With All-Cause and Cardiovascular Mortality
Elevated Vitamin B12 as a Predictor of Mortality in Hospitalized Patients
Vitamin B12 Fact Sheet for Health Professionals
Association of Serum Vitamin B12 Concentrations With Mortality