THF plays an important role in DNA synthesis, so reduced availability of THF results in ineffective production of cells with rapid turnover, in particular red blood cells, and also intestinal wall cells which are responsible for absorption
On top of that, proper function of the folate cycle is also required for synthesizing and regenerating a cofactor needed for the production of neurotransmitters (serotonin, melatonin, dopamine, noradrenaline, adrenaline) and nitric oxide
We can get vitamin B12 via certain foods though most of us are not getting enough
Additionally, if gastrointestinal adverse effects lead to reduced food intake or changes in dietary vitamin K consumption, warfarin dosing requirements may change
The National Institutes of Health Office of Dietary Supplements has not set a Tolerable Upper Intake Level for B12 precisely because no reliable evidence of harm from high intakes has been established in healthy people
Prospective monitoring In daily practice, I often ask my patients with B12 deficiency to maintain a sheet with their most prominent symptoms