What is the normal range of B12 by age?

October 9, 2025 •

4 min read

According to the National Institutes of Health (NIH), a serum vitamin B12 level above 300 picograms per milliliter (pg/mL) is considered sufficient for adults. However, the normal range of B12 by age is not static, as a person's ability to absorb this vital nutrient can change over their lifetime, particularly in older adulthood.

Quick Summary

This guide details the typical B12 ranges for different age groups, from infants to seniors. It also explains what can cause levels to be low or high, and how lifestyle factors can impact B12 absorption and status.

Key Points

Normal Ranges Fluctuate: The normal range of serum B12 (typically 200-900 pg/mL) varies by age, with infants and children often having higher levels and older adults having specific considerations due to absorption issues.
Older Adults at Risk: As people age, stomach acid decreases, hindering B12 absorption and increasing the risk of deficiency. Ideal levels for seniors are often cited as 300-350 pg/mL.
Vegans Require Supplements: Vitamin B12 is primarily found in animal products, making supplementation or fortified foods essential for vegans and strict vegetarians.
Deficiency Symptoms are Diverse: Signs of low B12 can be physical (fatigue, pale skin), neurological (numbness, cognitive decline), or psychological (depression) and should not be dismissed as simple aging.
Absorption is Key: Dietary intake is just one part of the equation; conditions like pernicious anemia, Crohn's disease, and certain medications can impair the body's ability to absorb B12 effectively.
Regular Monitoring is Advised: People at high risk, like older adults or those with specific medical conditions, should have their B12 levels checked regularly to prevent serious complications.

Understanding the Normal Ranges of Vitamin B12

Determining a 'normal' vitamin B12 range is not always straightforward, as ranges can vary between different laboratories and population studies. However, general guidelines exist to help interpret test results. It is important to look at these ranges in the context of one's individual health, as what is 'sufficient' for a young adult might be 'borderline' for an elderly person. The normal range is typically defined as a blood serum level of 200-900 picograms per milliliter (pg/mL), with anything below 200 pg/mL considered deficient. Borderline levels, often cited as 200-300 pg/mL, may warrant further investigation, such as testing for methylmalonic acid (MMA) to confirm a functional deficiency.

Normal B12 Ranges by Age Group

Infants and Children

Infants and younger children often have higher baseline B12 levels than adults, which can fluctuate as they grow. The NIH provides Recommended Dietary Allowances (RDA) that increase with age. For infants, adequate intake is around 0.4-0.5 mcg daily. By ages 9-13, the RDA rises to 1.8 mcg, before reaching the standard adult recommendation. It's especially crucial for babies of vegan or vegetarian mothers to receive sufficient B12 through supplementation or fortified foods, as breast milk from a deficient mother can lead to deficiency in the infant.

Infants (0–6 months): 0.4 mcg Adequate Intake (AI)
Children (1–3 years): 0.9 mcg RDA
Children (4–8 years): 1.2 mcg RDA
Teenagers (14–18 years): 2.4 mcg RDA

Adults

For adults (age 19 and older), the standard daily recommended intake is 2.4 mcg. For most, this amount is easily met through a diet rich in animal products. The serum concentration considered sufficient is generally above 300 pg/mL, though some may feel better with levels in the middle to upper part of the normal range. People with digestive issues or those on certain medications may need higher amounts or struggle with absorption despite adequate dietary intake.

Pregnant and Breastfeeding Individuals

During pregnancy and breastfeeding, the demand for B12 increases to support the baby's development. Pregnant women are advised to consume 2.6 mcg daily, and breastfeeding women need 2.8 mcg. Blood B12 levels can naturally drop during pregnancy but typically return to normal postpartum. Adequate intake is essential to prevent developmental problems in the baby.

Older Adults

Older adults, especially those over 60, face a higher risk of B12 deficiency. A key reason is reduced stomach acid production, which is necessary to free B12 from the food protein for absorption. The NIH indicates that ideal levels for seniors might be in the 300-350 pg/mL range. In older adults, symptoms of deficiency like cognitive issues or neuropathy might be mistaken for age-related decline. Supplements or injections are often necessary to maintain healthy levels.

Factors Influencing B12 Levels

Various factors beyond age can affect an individual's B12 status. A person's diet is a primary determinant, especially for vegans and strict vegetarians who must seek B12 from fortified foods or supplements since the vitamin is found almost exclusively in animal products. Medical conditions can also impact absorption. Autoimmune conditions like pernicious anemia prevent the production of intrinsic factor, a protein needed for B12 absorption. Digestive disorders such as Crohn's or celiac disease, and certain gastrointestinal surgeries, can also impair absorption. Additionally, medications such as metformin for diabetes and some heartburn drugs (proton pump inhibitors) can interfere with B12 absorption.

Comparison of B12 Ranges and Needs by Life Stage


Life Stage	Daily Recommended Intake (RDA/AI)	Typical Serum Range (pg/mL)	Primary Absorption Consideration
Infants	0.4-0.5 mcg (AI)	215–1389 ng/L (different unit)	Maternal intake, early dietary sources
Children	0.9-1.8 mcg	332-1494 ng/L (variable by age)	Dietary sources, balanced nutrition
Adults (19+)	2.4 mcg	>300 (sufficient), 200-300 (borderline)	Dietary intake, overall digestive health
Pregnant	2.6 mcg	Often decreases during pregnancy	Fetal development, increased demands
Breastfeeding	2.8 mcg	Return to normal postpartum	Maternal dietary intake, infant needs
Older Adults (60+)	2.4 mcg (Higher intake often needed)	300-350 (ideal), 200-900 (normal)	Decreased stomach acid, absorption issues

Common Symptoms of B12 Deficiency

Recognizing the symptoms of B12 deficiency is crucial, as early detection can prevent irreversible nerve damage. Symptoms can be vague and develop gradually, often mimicking other conditions or even normal aging.

Physical: Fatigue, weakness, pale skin, sore tongue, weight loss
Neurological: Numbness or tingling in extremities, walking difficulties, vision problems, memory loss, confusion
Psychological: Depression, irritability, personality changes

Dietary Sources of Vitamin B12

Since B12 is not naturally produced by the body, dietary intake is vital. The vitamin is abundant in animal-based foods. Vegetarians and vegans must rely on fortified foods or supplements to meet their needs.

Meat: Beef, lamb, and liver are excellent sources.
Fish and Shellfish: Salmon, tuna, and clams contain high amounts of B12.
Dairy: Milk, yogurt, and cheese are good sources.
Eggs: One large egg provides a notable amount of B12.
Fortified Foods: Many cereals, nutritional yeast, and non-dairy milks are fortified with B12.

Conclusion

What is the normal range of B12 by age varies significantly and is influenced by a complex interplay of diet, age, and individual health factors. While general guidelines exist, an individual's specific needs and absorption capabilities can change over time, particularly in older adults. Maintaining adequate B12 is essential for nerve health, DNA synthesis, and red blood cell production. People at higher risk, such as vegans, those with digestive disorders, or the elderly, should consult a healthcare provider for testing and discuss supplementation. Monitoring B12 levels throughout life is a proactive step toward overall well-being and preventing potential complications from deficiency. Regular check-ups and a balanced diet can help ensure that everyone, regardless of age, maintains optimal vitamin B12 levels.

Visit the National Institutes of Health website for more on dietary supplements.

Frequently Asked Questions

For teenagers aged 14 to 18, the Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 micrograms (mcg) per day. Specific serum ranges can vary, but staying within a healthy dietary intake is the primary goal.

Older adults need more B12 because their bodies often produce less stomach acid, which is necessary to break down vitamin B12 from food for proper absorption. This makes supplementation or fortified foods an important part of their diet to maintain optimal levels.

A serum B12 level below 200 pg/mL is generally considered a deficiency. Levels between 200 and 300 pg/mL are often considered borderline and may require additional testing to confirm a functional deficiency.

While uncommon, excessively high B12 levels may indicate underlying conditions such as liver disease, kidney problems, or certain forms of leukemia. Excess B12 from supplements is generally excreted by the body, but persistently high levels should be investigated by a doctor.

Foods rich in B12 include meat, poultry, eggs, and dairy products. Fortified foods like certain cereals, nutritional yeast, and plant-based milks are also good sources, especially for vegans and vegetarians.

B12 injections are typically used for individuals with severe deficiencies or absorption problems, like those with pernicious anemia, as they bypass the digestive system entirely. For mild to moderate deficiencies, or for maintenance, high-dose oral supplements are often just as effective.

Yes, some medications can impact B12 absorption. These include metformin (for diabetes), proton pump inhibitors (for heartburn), and H2 blockers.