Vitamin B12: What It Does, How Much You Need, and Who's at Risk of Low Levels

A plain-English guide to the vitamin your nerves and red blood cells cannot do without.

Want to see how much vitamin B12 you actually get? Track it free with Ration →

By the Ration Editorial Team · Reviewed against primary research · Updated July 14, 2026

Vitamin B12, also called cobalamin, is a water soluble vitamin that the body cannot make on its own.

It has to come from food or supplements.

Unlike most water soluble vitamins, B12 is stored in the liver in fairly large amounts.

That storage means it can take years for a deficiency to show up, even if intake drops to nearly zero.

Vitamin B12 works alongside folate to help make DNA and red blood cells.

It is also required to keep the protective myelin sheath around nerve cells intact, which is why deficiency can cause tingling, numbness, or balance problems.

B12 helps convert homocysteine, an amino acid, into methionine. Without enough B12, homocysteine can build up in the blood.

It also plays a role in energy metabolism, helping cells convert fat and protein into usable fuel.

• Vegans and strict vegetarians, since B12 is naturally found only in animal foods
• Older adults, who often produce less stomach acid needed to absorb B12 from food
• People with digestive conditions like Crohn's disease or celiac disease
• Anyone who has had gastric bypass or other stomach surgery
• People taking long term acid reflux medications or metformin
• Pregnant and breastfeeding people, who have higher B12 needs

Early deficiency can be vague: fatigue, weakness, and mild brain fog.

Left unaddressed, low B12 can lead to megaloblastic anemia, where red blood cells become large and abnormal.

• Numbness or tingling in hands and feet
• Difficulty walking or balance problems
• Memory issues or mood changes
• A swollen, inflamed tongue
• Pale or jaundiced skin

Nerve related symptoms can sometimes appear even when standard blood tests look normal, which is one reason deficiency is considered tricky to diagnose in its early stages.

Vitamin B12 is concentrated in animal foods. Plant foods generally do not contain meaningful amounts unless they are fortified.

For people following a vegan diet, fortified foods like plant milks, nutritional yeast, and breakfast cereals are often the main non-supplement sources.

Most healthy adults need only a small amount of B12 each day, typically in the range of a few micrograms.

Needs are somewhat higher during pregnancy and breastfeeding.

Because absorption from food depends on stomach acid and a protein called intrinsic factor, older adults are often advised to get B12 from fortified foods or supplements, which are absorbed more reliably than the B12 naturally bound to meat and dairy.

• Cyanocobalamin, the most common and least expensive form used in supplements and fortified foods
• Methylcobalamin, an active form that some people prefer, though it is not clearly proven superior for absorption
• Hydroxocobalamin, often used in injections rather than oral supplements
• Sublingual tablets and sprays, marketed as bypassing digestion, though evidence they work better than standard pills is limited

For most people, the form matters less than simply getting enough B12 consistently.

People with significant absorption problems, such as pernicious anemia, often need B12 injections rather than oral supplements, since the underlying issue is absorption, not intake.

Vitamin B12 is considered very safe, even at doses well above typical daily needs, since it is water soluble and excess is excreted in urine.

No tolerable upper intake level has been set for B12 because toxicity is so rare.

Very high supplemental doses have occasionally been linked to mild skin reactions like acne or rosacea flare ups in sensitive individuals, but serious side effects are uncommon.

People taking metformin or long term acid reducing medications may want to be aware that these drugs can lower B12 absorption over time.

Vitamin B12 is a nutrient where deficiency is common in specific groups but rare in the general population that eats animal products regularly.

Vegans, older adults, and people with digestive or absorption issues are the ones who most often benefit from paying close attention to intake.

Fortified foods and standard supplements are generally effective and very low risk ways to close the gap.