NutriTracker
Tue, Aug 11
All nutrients

Vitamin B12

B12
vitaminwater-solublemeasured in mcg

Today

30-day average. Months to years of reserve, so only a sustained trend is meaningful.

6.8 mcg / 2.4 mcg283%

What it is

B12 is needed to make red blood cells and to maintain the insulating sheath around your nerves. It occurs naturally only in animal foods, so anyone eating plant-based needs fortified foods or a supplement — this is not optional. Your liver stores several years' worth, which is why deficiency takes a long time to appear and why one low day means nothing. The catch is that nerve damage from prolonged deficiency can be permanent, so it's worth not finding out the slow way.

Reference intake

Your daily target, personalised to your age and sex.

RDA
2.4 mcgmale_19_plus
Upper limit
none established

What the evidence says

Wording reflects how strong the evidence actually is.

  • Prevents megaloblastic anemia

  • Prevents irreversible peripheral and central neuropathy

  • Lowers plasma homocysteine

  • Has been associated with: reduces cardiovascular events or slows cognitive decline

Deficiency

vitamin B12 deficiency; pernicious anemia when caused by loss of intrinsic factor

Approximately 6% of adults under 60 and closer to 20% of adults over 60 in the US and UK, driven mainly by absorptive failure rather than low intake. Rates among people eating strictly plant-based without supplementation are far higher.

Early signs

  • fatigue and weakness
  • pins and needles in hands and feet
  • sore or smooth red tongue (glossitis)
  • difficulty concentrating
  • mild mood change

Higher risk

  • people eating vegan or strict vegetarian diets without supplementation
  • adults over 60 (atrophic gastritis reduces the acid needed to free B12 from food protein)
  • long-term metformin use
  • long-term proton pump inhibitor or H2 blocker use
  • pernicious anemia (autoimmune loss of intrinsic factor)
  • post-gastrectomy or ileal resection
  • Crohn's disease affecting the terminal ileum

Excess

No adverse effects have been associated with excess B12 intake from food or supplements in healthy people.

From supplements

  • no established toxicity
  • acneiform eruptions and rosacea flares reported at very high supplemental doses, uncommonly

Absorption

~50% of a small dose; falls sharply as dose rises because intrinsic-factor-mediated uptake saturates near 1.5–2 mcg per meal

Helps absorption

  • adequate gastric acid (frees B12 from food protein)
  • intact intrinsic factor production
  • splitting intake across meals rather than one large dose
  • crystalline B12 in fortified foods and supplements — does not require gastric acid to be released

Hinders absorption

  • atrophic gastritis and reduced gastric acid
  • proton pump inhibitors and H2 blockers
  • metformin (interferes with ileal uptake)
  • loss of intrinsic factor (pernicious anemia)
  • terminal ileal disease or resection
  • heavy alcohol use

Top sources

Per 100 g, in mcg. FoodData Central IDs are resolved by the importer, not written by hand.

  • Clams, cooked

    85 g

    98.9 mcg

  • Beef liver, cooked

    85 g

    70.6 mcg

  • Nutritional yeast, fortified

    16 g (2 tbsp)

    50 mcg

  • Sardines, canned in oil

    92 g (1 can)

    8.9 mcg

  • Beef, ground, cooked

    85 g

    2.6 mcg

  • Egg, whole, cooked

    50 g (1 large egg)

    1.1 mcg

Ranking these by what you already eat needs the real log — see docs/STATUS.md.

Sources

Last reviewed 2026-08-11