Vitamin B12

A normal Vitamin B12 is 200 – 900 pg/mL. Higher is better.

Vegans and strict vegetarians are at high risk because B12 is found almost exclusively in animal products (meat, fish, eggs, dairy). Older adults often develop malabsorption from reduced stomach acid production (atrophic gastritis) or use of acid-blocking medications like PPIs and H2 blockers.

Pernicious anemia, an autoimmune condition that destroys the cells needed to absorb B12, is a classic cause. Metformin (a common diabetes drug) can lower B12 levels over time and should be monitored. Crohn's disease and gastric bypass surgery impair absorption as well.

If you eat animal products regularly, you likely get enough B12 from diet alone. Vegans should supplement or eat B12-fortified foods (nutritional yeast, fortified plant milks, fortified cereals). Sublingual tablets or injections bypass absorption issues for people who cannot absorb B12 from food. If you take a PPI or metformin long-term, ask your doctor about periodic B12 monitoring.