Most people get enough vitamin B12 from food, but several specific groups face a real risk of deficiency and benefit from supplementation. These include adults over 50, vegans and vegetarians, people on certain long-term medications, pregnant and breastfeeding women, and anyone with digestive conditions that impair absorption. The recommended daily intake for most adults is 2.4 micrograms, though supplement doses are often much higher to compensate for incomplete absorption.
Vegans and Vegetarians
B12 is found almost exclusively in animal products: meat, fish, eggs, and dairy. If you eat little or none of these foods, your risk of deficiency climbs sharply. A large review of studies found deficiency rates as high as 86.5% among adult vegans who don’t supplement. Even lacto-ovo vegetarians, who eat eggs and dairy, show meaningful deficiency rates, though lower than vegans. Among vegetarian children and adolescents, deficiency ranged from 0% to 33% depending on the study and the strictness of the diet.
Your body stores B12 in the liver, and those reserves can last several years. This means a new vegan might feel fine for a long time before symptoms appear, which creates a false sense of security. If you follow any plant-based diet, a daily B12 supplement or fortified foods (like nutritional yeast, fortified plant milks, or fortified cereals) is not optional. It’s essential.
Adults Over 50
An estimated 10% to 15% of people over 60 are deficient in B12, even if they eat plenty of meat and dairy. The problem isn’t diet. It’s absorption. As you age, the stomach lining gradually thins in a condition called atrophic gastritis, which reduces the acid needed to separate B12 from the proteins in food. Without enough stomach acid, B12 stays locked in the food and passes through unabsorbed.
Atrophic gastritis also allows bacteria to overgrow in the stomach and small intestine. These bacteria can bind B12 and use it themselves before your body gets a chance to absorb it. The key detail here: the crystalline form of B12 found in supplements and fortified foods does not require stomach acid for absorption. So even though your body struggles with the B12 in a steak, it can still absorb B12 from a pill or fortified cereal. That’s why major health guidelines specifically recommend that adults over 50 get their B12 from supplements or fortified foods rather than relying on diet alone.
People on Metformin or Acid-Reducing Medications
Two of the most widely prescribed drug categories in the world can quietly drain your B12 levels over time.
Metformin, the standard first-line treatment for type 2 diabetes, interferes with B12 absorption in the small intestine. With long-term use, deficiency rates may reach up to 50%. While this typically develops after about five years of use, cases have been reported after just three to four months. If you take metformin, periodic B12 monitoring is worth discussing with your provider.
Proton pump inhibitors (PPIs), commonly prescribed for acid reflux and ulcers, suppress stomach acid production. That’s their purpose, but it also mimics the absorption problem seen in older adults. Studies have found deficiency in over half of long-term users of common PPIs. H2 blockers and antacids carry a similar, though somewhat lower, risk. The longer you take any of these medications, the more important it becomes to watch your B12 status.
People With Pernicious Anemia or Digestive Conditions
To absorb B12, your stomach must produce a protein called intrinsic factor. In pernicious anemia, an autoimmune condition, the body creates antibodies that either block B12 from binding to intrinsic factor or prevent the B12-intrinsic factor complex from being absorbed in the small intestine. Either way, dietary B12 never reaches your bloodstream. People with pernicious anemia typically need B12 injections because even high-dose oral supplements may not be absorbed reliably.
Other digestive conditions that damage or bypass the section of the small intestine where B12 is absorbed can create similar problems. These include Crohn’s disease (particularly when it affects the lower portion of the small intestine), celiac disease, and any prior surgery that removed part of the stomach or intestine. If you have one of these conditions, your doctor may check B12 levels as part of routine monitoring.
Pregnant and Breastfeeding Women
The recommended intake rises to 2.6 mcg daily during pregnancy and 2.8 mcg while breastfeeding. These increases reflect the baby’s developing nervous system, which depends on adequate B12 from the mother. Research from the ECLIPSES study found that higher maternal B12 levels in the first trimester were associated with better motor, language, and cognitive performance in newborns compared to mothers with lower levels.
Deficiency during pregnancy is surprisingly common among vegetarian women, with rates between 17% and 39% depending on the trimester. Among infants born to deficient mothers, deficiency rates reached 45% in some studies. Because breast milk B12 content directly reflects the mother’s levels, a breastfeeding vegan or vegetarian who doesn’t supplement may deliver very little B12 to her infant during a critical window of brain development.
What B12 Deficiency Feels Like
Mild deficiency often has no obvious symptoms, which is part of what makes it dangerous. As it worsens, common signs include fatigue, weakness, and a type of anemia where red blood cells become abnormally large and inefficient at carrying oxygen.
The neurological symptoms are what make B12 deficiency particularly concerning. These can include tingling or numbness in the hands and feet, pain that radiates through the arms, difficulty with balance, and muscle weakness. Some people develop anxiety, mood changes, or cognitive fog. In one documented case, a physician experienced wrist pain, hand numbness, shooting pain in his arm and chest, and escalating anxiety, all of which resolved completely within two weeks of B12 treatment and had not returned 25 months later. Early treatment can lead to full or partial reversal of nerve damage, but the longer deficiency persists, the less likely complete recovery becomes.
How Much to Take
The recommended daily amount for most adults is 2.4 mcg, easily met through a normal diet that includes animal products. Supplements, however, are typically sold in much higher doses, often 500 to 1,000 mcg. This isn’t because you need that much. It’s because only a fraction of an oral dose is absorbed, especially at higher amounts. No toxic upper limit has been established for B12, though some evidence suggests that doses above 25 mcg per day over time may slightly increase the risk of bone fractures.
For treating a confirmed deficiency, oral doses up to 1,000 mcg daily are generally considered safe and effective. Sublingual tablets (dissolved under the tongue) are marketed as better absorbed, but evidence that they outperform standard oral supplements is limited. For people with pernicious anemia or severe absorption problems, injections bypass the digestive system entirely and are the most reliable option.
If you fall into any of the groups above, a simple blood test can check your levels. Normal B12 ranges for adults fall between roughly 200 and 600 pmol/L, though levels at the low end of “normal” can still cause symptoms in some people. A second marker called methylmalonic acid provides a more sensitive read on whether your cells are actually getting enough B12, since it rises when functional B12 is low even if serum levels appear borderline.