Deficiency is more common than most people realize and is linked to persistent fatigue, brain fog, mood changes, and slow metabolism
Conclusion Whilst severe B12 deficiency has a clear clinical picture with characteristic haematological and/or neurological features, establishing mild or borderline deficiency can be problematic as serum levels are maintained at the expense of tissue concentrations, and therefore serum levels of B12 may be in the low normal or borderline range despite a deficiency
It is not evidence that every vial using the same name contains that molecule
Certain health conditions such as intestinal or stomach problems, poor nutrition, cancer, HIV, pregnancy, old age, veganism, and alcoholism can cause vitamin B12 deficiency
It is not a single compound and not a pharmaceutical product