Hi, I understand your concern. Vitamin B12 has many important roles to play in our body.It helps in making red blood ceels, DNA in our body. It is concerned with nerve conduction. Less vitamin does give rise to tiredness. SOurce of B12 is non vegetarian food ( meat,poultry ,sea food, dairy products). fortified cerels,multivitamin pills containing B12. If absorption is the problem, Injectable , Vit B12 should be taken. Thanks.