Vitamin B12 deficiency affects roughly 3.6% of adults in the United States, based on national survey data collected between 2007 and 2018. That number sounds modest, but it only counts people whose blood levels have dropped below the clinical deficiency threshold. When you include people with low-but-not-yet-deficient levels, the picture changes dramatically: about 1 in 8 U.S. adults falls into this broader category, and in some populations the rate climbs much higher.
Deficiency vs. Low Status: Why the Numbers Vary
Much of the confusion around B12 statistics comes down to where you draw the line. Clinical deficiency is typically defined as a blood level below 200 pg/mL. At that cutoff, about 3.6% of American adults qualify. But there is a gray zone between 200 and 300 pg/mL where the body doesn’t have a comfortable surplus and subtle problems can develop over time. When that range is included, the prevalence jumps to roughly 12.5% of all adults. Among people who don’t take B12 supplements, it reaches about 16.3%.
Some researchers put the number even higher. Epidemiological studies in industrialized countries have estimated B12 deficiency at around 20% of the general population when broader definitions are used, and low or marginal B12 status may affect up to 40% of Western populations, particularly among people who eat few animal-based foods. The takeaway: full-blown deficiency with obvious symptoms is uncommon, but quietly low B12 levels are not.
Who Is Most at Risk
Age is one of the strongest risk factors. In large surveys in the U.S. and the U.K., about 6% of people aged 60 and older are clearly deficient, and closer to 20% have marginal status. The Framingham Heart Study found a 12% deficiency rate among older adults living independently in the community. In nursing homes and hospitals, that figure rises to 30% to 40%.
The reason is partly biological. As you age, your stomach produces less acid and less of a protein called intrinsic factor, both of which are needed to pull B12 out of food and absorb it. Surgical removal or bypass of part of the stomach eliminates intrinsic factor production entirely, making lifelong supplementation necessary.
People who eat little or no animal products are another high-risk group. B12 is naturally found almost exclusively in meat, fish, dairy, and eggs. Without supplementation or fortified foods, vegans and many vegetarians are likely to develop low levels over time.
Pregnancy increases risk as well. A large meta-analysis found that B12 insufficiency affected about 21% of women in the first trimester and rose to 29% by the third trimester. These rates were high even in nonvegetarian populations, and they were especially elevated in parts of South Asia and the Eastern Mediterranean.
In developing countries, deficiency is far more common across all age groups, starting in early childhood and persisting throughout life, largely due to limited access to animal-sourced foods.
Why B12 Is Hard to Absorb
B12 absorption is more complicated than most vitamins. Your stomach lining produces intrinsic factor, a specialized protein that binds to B12 and escorts it to the lower part of the small intestine, the only place where it can cross into the bloodstream. If any step in this chain breaks down, you can eat plenty of B12-rich food and still become deficient.
The most well-known absorption failure is pernicious anemia, an autoimmune condition where the immune system attacks the cells that make intrinsic factor. Other common causes include chronic gastritis, celiac disease, Crohn’s disease, and long-term use of acid-reducing medications, all of which interfere with the stomach’s ability to release or absorb the vitamin. Because the body stores several years’ worth of B12 in the liver, these conditions can quietly deplete reserves for a long time before symptoms appear.
Symptoms That Develop Slowly
B12 deficiency tends to creep up gradually, which is part of what makes it easy to miss. Early signs are often vague: persistent fatigue, mild weakness, or a general sense of not feeling right. As levels drop further, you may notice a sore tongue or mouth ulcers, pale skin, nausea, or unexplained weight loss.
The neurological symptoms are the ones that worry doctors most. Numbness or tingling in the hands and feet is common, sometimes described as a “pins and needles” sensation that doesn’t go away. Memory problems, confusion, difficulty walking, and changes in speech can follow. These nerve-related effects can sometimes become permanent if the deficiency goes untreated for too long, which is why catching low levels before symptoms develop matters.
B12 also plays a central role in making red blood cells. When it runs low, the body produces abnormally large, dysfunctional red blood cells that can’t carry oxygen efficiently. This leads to a specific form of anemia that compounds the fatigue and weakness.
How B12 Deficiency Is Detected
A standard blood test measuring serum B12 is the usual first step. The result will fall into one of three ranges: clearly deficient (below 200 pg/mL), borderline (200 to 300 pg/mL), or normal (above 300 pg/mL). The borderline zone is where interpretation gets tricky, because some people in that range feel fine while others are already experiencing subtle effects.
When results are ambiguous, a second test measuring methylmalonic acid (MMA) can help clarify the picture. MMA is a compound that builds up in the blood when B12 is too low for normal cell metabolism. An elevated MMA level, even alongside a borderline B12 reading, points toward a true functional deficiency. Your provider may also check a related marker called homocysteine, which rises for similar reasons.
Supplementation Makes a Clear Difference
The gap between supplement users and nonusers is striking. Among U.S. adults who take a B12 supplement, only about 5.9% have insufficient levels. Among those who don’t supplement, 16.3% are insufficient. That threefold difference helps explain why some population-level statistics look reassuring while individual risk can be quite high depending on diet and habits.
Most adults in the U.S. meet the estimated average requirement for B12 through food alone, but “meeting the average” still leaves a meaningful minority falling short, especially among older adults whose absorption is declining regardless of intake. For people over 50, many nutrition guidelines recommend getting B12 from fortified foods or supplements rather than relying solely on dietary sources, because the synthetic form doesn’t require stomach acid to be absorbed.