Scientists warn that current vitamin B12 guidelines may be putting your brain at risk

The UCSF findings do not prove that lower active B12 directly causes cognitive decline, and they do not mean every older adult should begin taking supplements without medical guidance. They do, however, suggest that the current definition of B12 deficiency may be too blunt for brain health.
For clinicians, the study points to the possible value of looking beyond total B12, especially when older patients have neurological symptoms.