what is the difference between b12 and b complex
â¢ B complex is mainly absorbed in the jejunum, but B12 are absorbed in the ileum. â¢ B complex is related to the general cellular metabolism, whereas B12 is specific to the nervous system and the blood cells.â¢ B complex has no toxicity effects, and b12 has low toxicity. â¢ The dietary sources of B complex are mainly based on vegetable and grain products, but B12 is mainly in animal products.itamin B12 vs B Complex. Nutrition and nutritional supplements have come a long way from stored melons in ships to be given to journeying sailors to avoid the scurvy, to pop in the mouth tablets over the past two centuries.