Nutrient explainer · Energy & Vitality

Low on vitamin B12? What it means and what to eat

Feeling run-down has many possible causes. Vitamin B12 is one worth knowing about, especially if you're over 50 or eat mostly plants.

By the Herbal Bee teamUpdated 5 min read

A man talking with his doctor at a bright clinic desk

This page explains who runs low and where to find B12. It can't tell you your B12 status. Only a blood test can.

What B12 does in your body

B12 helps your body build red blood cells, make DNA and keep nerves working normally [1]. Evidence: A — NIH fact sheet.

Your body stores about 1–5 mg, so low intake can take years to show up [1].

Who tends to run low

These groups are more likely to have low B12 [1]. Evidence: A — NIH fact sheet, drawing on observational data.

  • Adults over 50. Many make less stomach acid, which helps free B12 from food. Atrophic gastritis, a thinning of the stomach lining, affects about 8–9% of adults 65 and older. Low B12 shows up in 3% to 43% of older adults, depending on the definition [1].
  • Plant-based eaters. B12 occurs naturally only in animal foods. Babies breastfed by vegan mothers can also run low [1].
  • People taking metformin. In a long-term US study, 4.3% of metformin users had low B12 after 5 years, vs 2.3% on placebo [5]. Evidence: B — analysis of a large trial.
  • People on long-term acid reducers, such as omeprazole [1].
  • People with pernicious anemia, celiac disease, or stomach or weight-loss surgery [1].

What low B12 can lead to

Low B12 can contribute to [1][2]:

  • tiredness or weakness
  • pale skin or a pounding heartbeat
  • numbness or tingling in the hands and feet
  • balance problems
  • memory trouble or low mood
  • megaloblastic anemia, a type of low red blood cell count

Nerve symptoms can happen even without anemia [1]. Evidence: A.

These are signs worth asking your doctor about, not a checklist. Many other things cause the same feelings.

Testing is the only way to know. A doctor may check serum B12, and sometimes methylmalonic acid (MMA) or homocysteine [1]. If you're in a group above, ask whether testing makes sense.

How much you need

Most people 14 and older need 2.4 mcg a day: 2.6 mcg in pregnancy, 2.8 mcg while breastfeeding. No upper limit has been set [1]. Evidence: A.

Group Daily amount
Infants 0–6 months 0.4 mcg (AI)
Infants 7–12 months 0.5 mcg (AI)
Children 1–3 0.9 mcg (RDA)
Children 4–8 1.2 mcg (RDA)
Children 9–13 1.8 mcg (RDA)
Teens 14–18 (boys and girls) 2.4 mcg (RDA)
Men and women 19–50 2.4 mcg (RDA)
Men and women 51+ 2.4 mcg (RDA)
Pregnancy 2.6 mcg (RDA)
Breastfeeding 2.8 mcg (RDA)

No upper limit has been set.[1]

Top food sources

B12 comes naturally from clams, fish, meat, eggs and dairy. Plant-based? Fortified nutritional yeast, cereals and plant milks do the work [1]. Amounts vary by brand, so check the label's %DV. Tempeh, spinach and beans have little or none.

Vitamin B12

Food Serving Amount
Clams, cooked 3 oz 17 mcg (708% DV)
Nutritional yeast, fortified Vegan · Vegetarian about ¼ cup (8.3–24 mcg; varies by brand, check label) 8.3 mcg (346% DV)
Salmon, Atlantic, cooked 3 oz 2.6 mcg (108% DV)
Tuna, light, canned in water 3 oz 2.5 mcg (104% DV)
Ground beef, 85% lean, cooked 3 oz 2.4 mcg (100% DV)
Milk, 2% Vegetarian 1 cup 1.3 mcg (54% DV)
Yogurt, plain, fat-free Vegetarian 6 oz 1 mcg (43% DV)
Breakfast cereal fortified with 25% DV Vegan · Vegetarian 1 serving (varies by brand, check label) 0.6 mcg (25% DV)
Egg, whole, cooked Vegetarian 1 large 0.5 mcg (19% DV)
Cheddar cheese Vegetarian 1½ oz 0.5 mcg (19% DV)
Turkey breast, roasted 3 oz 0.3 mcg (14% DV)
Tempeh Vegan · Vegetarian ½ cup 0.1 mcg (3% DV)
Beans, spinach, bananas, whole wheat bread Vegan · Vegetarian standard serving 0 mcg (0% DV)

Daily Value: 2.4 mcg[1]

%DV uses the 2.4 mcg Daily Value. Amounts come from the NIH fact sheet, which draws on USDA FoodData Central [1].

Food first, then supplements

Over 50? Experts advise getting most of your B12 from fortified foods or supplements, which don't depend on stomach acid the way food B12 does [2][3]. Evidence: A.

Forms. Cyanocobalamin is the most common supplement form. Methylcobalamin is an active form. Research hasn't shown any form is absorbed better [1].

Absorption. You absorb about half of a 1–2 mcg dose, but only about 2% of 500 mcg and 1.3% of 1,000 mcg [1].

Too much? B12 is generally considered safe, even at high doses [1].

Interactions. Metformin, PPIs and H2 blockers can lower absorption [1]. Pregnant, breastfeeding, or choosing for a child? Ask your doctor first.

A note on folate. Large amounts of folate can correct the anemia of low B12, but not the nerve damage [4]. That can hide low B12. The adult upper limit for synthetic folate, including folic acid and methylfolate, is 1,000 mcg a day [4]. On high-dose folate? Ask about checking your B12.

Where B12 appears in our products

B12 helps the body make red blood cells and supports normal nerve function* [1]. Evidence: A for B12's role. No studies of these products exist. Individual results vary.

  • 5-MTHF Methylfolate: methylcobalamin with methylfolate, B6, riboflavin and TMG.* B12: 3 mg (3,000 mcg) per serving. Its 3 mg (3,000 mcg) of methylfolate is above the 1,000 mcg upper limit [4], so read the folate note and talk with your doctor first.
  • Advanced Alpha Focus: B6 and B12 alongside its focus ingredients.* B12: 10 mcg per serving.
  • Gut Health: B vitamins, including B12.* B12: 100 mcg per serving.

Plant-based? Advanced Alpha Focus is labeled vegan. Ask us about 5-MTHF and Gut Health.

Quick answers

Can I get enough vitamin B12 on a vegan diet?
Yes, with planning. B12 occurs naturally only in animal foods, so vegans rely on fortified foods such as nutritional yeast, cereals and plant milks, or a supplement. Amounts vary by brand, so check labels for vitamin B12 and %DV [1].

How much vitamin B12 do adults need?
Most people 14 and older need 2.4 mcg a day, 2.6 mcg during pregnancy and 2.8 mcg while breastfeeding. Adults over 50 are advised to get most of it from fortified foods or supplements [1][2].

Can you take too much vitamin B12?
No upper limit has been set, because B12 has a low potential for harm, and it is generally considered safe even at high doses. Still, tell your doctor or pharmacist about every supplement you take [1].

Is methylcobalamin better absorbed than cyanocobalamin?
Research hasn't shown a difference. Methylcobalamin is one of the active forms your body uses, and your body converts cyanocobalamin into active forms. The NIH fact sheet says no evidence shows absorption differs by form [1].

How do I know if my B12 is low?
Only a blood test can tell. A doctor may order a serum B12 test and sometimes methylmalonic acid (MMA) or homocysteine. Ask about testing if you're over 50, eat plant-based, take metformin or long-term acid reducers, or have had stomach or weight-loss surgery [1].

Keep reading

Not sure where to start? Take the "Energy and everyday tiredness" quiz.

Sources

  1. NIH ODS. Vitamin B12 fact sheet for health professionals, 2025. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
  2. NIH ODS. Vitamin B12 fact sheet for consumers, 2023. https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/
  3. Institute of Medicine. Dietary Reference Intakes, Chapter 9: Vitamin B12, 1998. https://www.ncbi.nlm.nih.gov/books/NBK114302/
  4. NIH ODS. Folate fact sheet for health professionals. https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/
  5. Aroda VR, et al. J Clin Endocrinol Metab, 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC4880159

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

This article is for general education and isn't medical advice.

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