Vitamin B12 deficiency is quietly common, and it develops slowly enough that many people adjust to feeling a little worse without connecting the dots. Because B12 is stored in the liver in relatively large amounts, a deficiency can take years to become symptomatic, which means by the time it’s caught, it’s often more advanced than a typical nutrient shortfall.
What B12 Actually Does
Vitamin B12 is essential for producing healthy red blood cells, maintaining the protective myelin sheath around nerves, and synthesizing DNA. It works closely with folate (vitamin B9) in several of these processes, which is why the two are often discussed together and why a deficiency in one can sometimes mask or mimic a deficiency in the other on standard blood tests.
How Much You Need
The RDA for vitamin B12 is 2.4 micrograms (mcg) per day for anyone 14 and older, rising slightly to 2.6 mcg during pregnancy and 2.8 mcg while breastfeeding. Unlike fat-soluble vitamins, there’s no established upper limit for B12, since excess amounts are simply excreted rather than accumulating to toxic levels.
Who Is Genuinely at Risk
- Adults over 50 — stomach acid naturally declines with age, and stomach acid is required to release B12 from food proteins before it can be absorbed
- People following vegan or strict vegetarian diets, since B12 occurs almost exclusively in animal products
- People with pernicious anemia, an autoimmune condition that prevents proper B12 absorption regardless of intake
- People who’ve had weight-loss or gastrointestinal surgery affecting the stomach or small intestine
- Long-term users of metformin (for diabetes) or acid-reducing medications like proton pump inhibitors
- Infants of mothers following vegan diets, who can develop deficiency through breast milk
Signs and Symptoms
- Fatigue and weakness
- Pale or slightly yellow-tinged skin
- A burning or pins-and-needles sensation in the hands or feet
- Difficulty walking or balance issues in more advanced cases
- Memory problems or mood changes
- A smooth, sore tongue
The neurological symptoms are the most important to catch early — unlike the fatigue and anemia-related symptoms, some nerve damage from prolonged B12 deficiency can become permanent if left untreated for too long. This is why adults over 50, and anyone in a higher-risk group, are generally advised to get periodic blood testing rather than waiting for symptoms.
Good Food Sources
- Clams and other shellfish: exceptionally high, often well over 1,000% DV per serving
- Beef liver
- Fish like salmon, trout, and tuna
- Eggs
- Dairy products (milk, yogurt, cheese)
- Fortified nutritional yeast and breakfast cereals (relevant for vegans)
Frequently Asked Questions
Should everyone over 50 take a B12 supplement? The NIH notes that most adults over 50 are advised to meet the majority of their B12 needs through supplements or fortified foods rather than relying solely on absorption from whole food protein, since natural stomach acid production tends to decline with age.
Can vegans get enough B12 from plant foods alone? No — B12 does not occur naturally in plant foods in meaningful amounts. Vegans need fortified foods or a supplement; this is one of the few nutrients where supplementation isn’t optional for a fully plant-based diet.
How is a B12 deficiency treated? Depending on severity and the underlying cause, treatment ranges from oral supplements to B12 injections, particularly for people whose deficiency stems from an absorption problem rather than low dietary intake.
Why B12 Deficiency Is Often Missed for So Long
Vitamin B12 is essential for nerve function, DNA synthesis, and red blood cell production, and unlike many nutrients, your body stores a multi-year reserve of it in the liver, which means deficiency typically develops slowly, sometimes over years, rather than showing up quickly the way some other nutrient deficiencies might. This slow onset is part of why B12 deficiency is frequently missed or misattributed to other causes for a long time, symptoms like fatigue, brain fog, and mood changes are nonspecific and easy to blame on stress, poor sleep, or simply getting older, when an underlying B12 deficiency is quietly and gradually worsening in the background, sometimes not caught until symptoms become more severe or a routine blood test happens to flag it.
Beyond fatigue and cognitive symptoms, deficiency can produce more specific signs worth recognizing, including tingling or numbness in the hands and feet (a sign of nerve involvement that can become permanent if deficiency goes uncorrected for too long), a smooth or sore tongue, balance problems, and in more severe or prolonged cases, memory problems that can be mistaken for early dementia in older adults, a misattribution that’s been documented and is part of why screening for B12 deficiency is a standard step when evaluating unexplained cognitive decline.
Who’s Actually at Risk
B12 is found almost exclusively in animal products, meat, fish, eggs, and dairy, which makes vegans and, to a lesser extent, vegetarians a well-recognized higher-risk group unless they’re supplementing or eating fortified foods. Older adults are another major risk group, not primarily due to diet, but because absorbing B12 from food requires adequate stomach acid, and stomach acid production naturally declines with age, meaning older adults can be eating plenty of B12-containing food yet still absorb too little. People taking long-term acid-reducing medications (like proton pump inhibitors) or metformin for diabetes, people with digestive conditions affecting absorption (like celiac disease, Crohn’s disease, or those who’ve had certain gastric surgeries), and people with pernicious anemia, an autoimmune condition specifically impairing B12 absorption, round out the higher-risk groups.
Because absorption, not just dietary intake, is such a common cause, someone eating a diet with plenty of B12-rich foods can still become deficient, which is why unexplained fatigue or neurological symptoms warrant actual bloodwork rather than assuming diet alone rules out deficiency.
Getting Tested and Treated
B12 deficiency is diagnosed through a blood test, and because the neurological symptoms of prolonged deficiency can become permanent if left uncorrected too long, it’s a condition worth taking seriously rather than self-treating with an over-the-counter supplement without confirming an actual deficiency and its underlying cause first, since the right treatment approach (oral supplementation versus injections, for instance) depends partly on why the deficiency is happening, particularly whether it’s dietary or an absorption issue. If you fall into one of the higher-risk groups above and have been experiencing unexplained fatigue, tingling, or cognitive symptoms, requesting a B12 test at your next doctor’s visit is a reasonable, low-cost way to rule this out.
Sources
- NIH Office of Dietary Supplements — Vitamin B12 Fact Sheet
- NIH Office of Dietary Supplements
- MedlinePlus (U.S. National Library of Medicine)
Final Thoughts
B12 deficiency is slow, common, and treatable, but it’s also one of the few nutrient deficiencies where waiting too long carries a real risk of permanent nerve damage. If you’re over 50, vegan, or take a medication known to interfere with B12 absorption, a periodic blood test is a reasonable, low-effort safeguard rather than something to defer indefinitely.
This article is for general educational purposes and is not a substitute for personalized medical advice.
About the Author
This article was written and reviewed by Sarah Whitfield, focused on translating public health information into clear, practical guidance for everyday readers. If you spot an error or have a correction, please contact us.