The vitamin deficiency that can be mistaken for normal aging

Two micrograms is an almost unimaginably small daily requirement — less than a fragment of a grain of table salt — yet a shortfall in vitamin B12 can produce fatigue, weakness, numbness, poor balance, memory problems and "brain fog" serious enough to be mistaken for ordinary aging, according to a 2026 explainer from a Quadram Institute biochemist.

Who’s actually at risk

B12 deficiency becomes markedly more common with age. Some older adults produce less stomach acid, which is required to release B12 from food; others develop autoimmune gastritis, which damages the stomach cells that produce both acid and the intrinsic factor protein needed for B12 absorption. Vegans and vegetarians are also at elevated risk because B12 occurs naturally almost exclusively in animal-derived foods (meat, fish, eggs, dairy), and certain medications for diabetes or acid reflux, along with weight-loss surgery, can further reduce absorption.

Why it hits energy, not just blood counts

The traditional story is that B12 deficiency causes tiredness because it impairs red blood cell production, leading to anaemia. But B12 is directly required by only two enzymes in the body — one for DNA synthesis, the other inside mitochondria, the structures that convert food into usable cellular energy. A 2026 study explored what happens when cells lack sufficient B12 and found it can interfere with mitochondrial DNA and reduce energy production in laboratory models of skeletal muscle, while a related study in aged mice found B12 supplementation improved mitochondrial number and structure in muscle tissue.

This mitochondrial role points to one possible reason some people with low B12 report fatigue before obvious anemia is even detected.

What this does — and doesn’t — mean for supplements

These findings do not mean B12 supplements reverse aging or boost energy in people whose levels are already normal — much of the underlying muscle-function research remains observational or animal-based, and the author is explicit that B12 injections at wellness clinics offer little benefit to people who aren’t actually deficient. The useful takeaway is narrower and more practical: persistent, unexplained fatigue, tingling or balance problems are worth checking with an actual blood test rather than assuming they’re an inevitable feature of getting older.

B12 is one of the markers Misi flags automatically from any lab PDF you upload, alongside ferritin and vitamin D — the small set of deficiencies that are cheap to test for, easy to correct, and disproportionately likely to be mistaken for "normal aging" when left unchecked.