How much vitamin B12 you need per day by age

Most healthy adults need 2.4 micrograms (mcg) of vitamin B12 per day, according to the NIH Office of Dietary Supplements. Needs differ slightly during childhood, pregnancy, and breastfeeding, and some groups absorb the vitamin less efficiently regardless of how much they consume.

Why vitamin B12 matters

Vitamin B12 plays three well-established physiological roles in the body. According to the NIH Office of Dietary Supplements, it is required for healthy red blood cell formation, for the development, myelination, and function of the central nervous system, and for DNA synthesis. The evidence supporting these roles is rated strong. A prolonged shortfall can lead to megaloblastic anemia, a condition in which red blood cells grow abnormally large and cannot carry oxygen efficiently.

It is worth being clear about what the research does not yet support. The NIH rates the evidence as insufficient to conclude that vitamin B12 supplementation reduces the risk of cardiovascular disease or stroke, improves cognitive function, slows dementia or Alzheimer's disease, boosts energy or athletic performance in people who are not deficient, or affects cancer risk. Supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA.

Recommended daily intakes by age

The figures below are Dietary Reference Intakes established by the National Academies of Sciences, Engineering, and Medicine and reported by the NIH Office of Dietary Supplements. The Recommended Dietary Allowance (RDA) is the average daily intake sufficient to meet the needs of nearly all healthy people in each group. For infants, an Adequate Intake (AI) is used instead because data are not sufficient to set a full RDA.

Infants

• 0 to 6 months: 0.4 mcg per day (AI)
• 7 to 12 months: 0.5 mcg per day (AI)

Children

• 1 to 3 years: 0.9 mcg per day (RDA)
• 4 to 8 years: 1.2 mcg per day (RDA)
• 9 to 13 years: 1.8 mcg per day (RDA)

Adolescents and adults

• 14 years and older: 2.4 mcg per day (RDA)

Pregnancy and breastfeeding

• Pregnant people of any age: 2.6 mcg per day (RDA)
• Breastfeeding people of any age: 2.8 mcg per day (RDA)

There is no established Tolerable Upper Intake Level for vitamin B12. The NIH notes that the vitamin is generally considered safe even at high doses, because the body does not store excess amounts and absorption becomes self-limiting at high oral doses. That said, higher doses are not the same as better outcomes, and population reference values are a reasonable starting point for most people.

Groups who may need to monitor their intake more closely

Getting enough B12 is not just about how much you consume. The body needs adequate stomach acid to separate B12 from the proteins in food before it can be absorbed. Several circumstances can interfere with that process.

Adults over 50

Gastric acid secretion tends to decline with age. Older adults may absorb B12 from supplements or fortified foods more reliably than from naturally occurring food sources, because those forms do not require the same acid-dependent separation step. The NIH recommends that adults over 50 meet most of their B12 needs through fortified foods or supplements for this reason.

People following a vegan or strict vegetarian diet

Vitamin B12 is found almost exclusively in animal-derived foods such as meat, fish, poultry, eggs, and dairy. People who avoid all animal products are at meaningful risk of deficiency over time and typically need a reliable supplemental source or fortified foods such as certain plant milks and breakfast cereals.

People with certain digestive conditions

Conditions that affect the stomach or small intestine, including atrophic gastritis and pernicious anemia, can reduce the body's ability to absorb B12 from food. People with these conditions should discuss their B12 status with a clinician, as they may need higher doses, injections, or other forms of supplementation.

People taking certain medications

Two categories of medication are known to interfere with vitamin B12 absorption, according to the NIH Office of Dietary Supplements.

• Gastric acid inhibitors: Proton pump inhibitors such as omeprazole (Prilosec) and lansoprazole (Prevacid) can interfere with B12 absorption from food by slowing gastric acid release and may lead to deficiency over time. Histamine H2-receptor antagonists such as cimetidine (Tagamet) and ranitidine (Zantac) can similarly reduce absorption.
• Metformin: This antihyperglycemic medication, used for prediabetes and type 2 diabetes, might reduce B12 absorption and has been shown to significantly lower serum B12 concentrations in some people.

If you take any of these medications, talk to your doctor or pharmacist before adding a B12 supplement, and ask whether periodic monitoring of your B12 levels makes sense for you. This applies to any supplement combined with prescription or over-the-counter medication.

Food sources of vitamin B12

For most people, a varied diet that includes animal products supplies adequate B12 without supplementation. Rich dietary sources include:

• Beef liver and other organ meats
• Clams and other shellfish
• Fish such as salmon, tuna, and trout
• Beef, pork, and poultry
• Eggs and dairy products including milk, yogurt, and cheese
• Fortified breakfast cereals and plant-based milks (check the label, as levels vary by brand)

When to talk to a clinician

The intakes listed in this guide are population reference values intended for general information. They are not a substitute for personalised medical advice. You should speak with a doctor or pharmacist if you are over 50 and have not had your B12 status checked recently, if you follow a diet that excludes all animal products, if you have a digestive condition that may affect absorption, if you take metformin or a gastric acid inhibitor, or if you are pregnant or breastfeeding and unsure whether your diet or prenatal supplement covers the recommended 2.6 to 2.8 mcg per day.

A simple blood test can assess your B12 status and help guide any decision about supplementation. Self-treating a suspected deficiency without a confirmed diagnosis is not recommended, because symptoms of B12 deficiency can overlap with other conditions that require different management.

Sources

• NIH Office of Dietary Supplements, Vitamin B12 Fact Sheet for Health Professionals: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
• NIH Office of Dietary Supplements, Vitamin B12 Fact Sheet for Consumers: https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/