These include the bell-shaped dose-response curve, central effects after peripheral administration, a delayed and prolonged time course, and some penetration of the blood-brain barrier in essentially intact form
The Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) tool was used to assess the certainty of the evidence for the two primary biochemical outcomesserum vitamin B12 concentration increase and homocysteine reductionacross all included studies, and separately for randomised controlled trials (RCTs) and observational studies
Tiredness, stress, ill-health, poor or limited diet will all reduce this absorption further. For some people, taking a vitamin B12 supplement is one of the easiest ways to maintain healthy levels
If symptoms progress, seek medical care
If youre looking for alternatives, its worth understanding options like liposomal B12 as a potential alternative
Thus, he warns that repeated observations of elevated homocysteine levels in vegans show that B12 intake must be addressed