The main causes of a vitamin B12 deficiency are as follows: Malabsorption due to poor intestinal health (inflammation, bacteria, fungal infection, parasites, disturbed intestinal flora) due to a lack of transport molecules (intrinsic factor), genetic diseases (cobalamin disease) or medications that hinder uptake
Every subsequent dose is double what you think it is
Journal of Applied Physiology , 110(3), 774-780
The tricky thing about fatigue is that its a symptom, not a diagnosis, and it can stem from a multitude of causes: Lifestyle Factors: Poor sleep, chronic stress, insufficient physical activity, or an unhealthy diet can all contribute