A normal B12 reading does not mean you have enough
Deficiency is judged on four markers, not one: the blood level, the share bound for delivery into cells, and two that build up when cells cannot use what is there.
What the study found
Fifteen percent of over-60s with no known risk were B12 deficient
Deficiency was judged on four markers, not one. Alongside the blood level sit holotranscobalamin, the share bound for delivery into cells, and homocysteine and methylmalonic acid, which build up when cells cannot use the B12 present. A normal level on its own settles less than it looks.
The caveat · Supplement takers were left out
This is a snapshot of one Irish and Northern Irish cohort recruited between 2008 and 2012, not a picture of what happens over time. Anyone already taking a B12 supplement was excluded, which sharpens the dietary signal but leaves out most real supplement users.