Vitamin B12 deficiency is a public health problem, especially among older people.
In a study involving more than 100 volunteers aged 61 to 87, all participants underwent annual clinical exams, MRI scans and cognitive tests, and had blood samples taken. Individuals with lower vitamin B12 levels at the start of the study had a greater decrease in brain volume. Those with the lowest B12 levels had a sixfold greater rate of brain volume loss compared with those who had the highest levels.
However, none of the participants were actually deficient in vitamin B12 — they just had low levels within a normal range.