Vitamin B12 Deficiency: The Silent Epidemic After Age 50

Vitamin B12 deficiency affects an estimated 10–20% of adults over 60 and more in people on long-term PPIs or metformin or eating strict vegetarian diets, largely because age-related atrophic gastritis cuts the stomach acid needed to free B12 from food. It is easy to miss: symptoms (fatigue, forgetfulness, numbness and tingling, low mood) get blamed on normal aging, and standard serum B12 can read normal while the more sensitive markers — methylmalonic acid and holotranscobalamin — are already abnormal. Catching it early matters because the neurological damage (subacute combined degeneration of the spinal cord) can become irreversible if deficiency persists for years, whereas most cases caught early are reversible. Anyone over 50, on long-term PPI or metformin therapy, or vegan should be tested, and high-dose oral or sublingual methylcobalamin (about 1,000 mcg/day) works even when intrinsic factor is impaired, because enough is absorbed by passive diffusion.

Why Absorption Declines With Age

B12 absorption from food requires stomach acid to release B12 from protein. Age-related atrophic gastritis reduces stomach acid production in a meaningful share of adults over 50. Long-term PPI use and metformin therapy each independently lower B12 absorption through different mechanisms. The American Family Physician 2017 review by Langan and Goodbred lists screening criteria including PPI use beyond 12 months, metformin use beyond 4 months, vegan or strict vegetarian diet, prior gastric or small-bowel surgery, and age over 75. Wolffenbuttel et al.'s 2020 NHANES analysis (Netherlands Journal of Medicine) showed that elevated methylmalonic acid (MMA) — a more sensitive marker than serum B12 — was more strongly tied to functional decline than serum B12 alone.

What Deficiency Looks Like

Early B12 deficiency elevates homocysteine and methylmalonic acid (MMA) before serum B12 falls below the standard laboratory reference range — meaning standard blood tests can miss it. Neurological effects — subacute combined degeneration of the spinal cord — can be irreversible if deficiency persists for years. Macrocytic anemia, cognitive decline, and peripheral neuropathy are the classic advanced presentations.

Testing and Supplementation

The most sensitive tests are serum methylmalonic acid and holotranscobalamin (active B12). Anyone over 50, anyone on long-term PPI or metformin therapy, and all vegans should be tested. Sublingual methylcobalamin at 1,000 mcg/day is effective even in people with impaired intrinsic factor, as passive diffusion provides adequate absorption at high doses.