Once you begin treating your vitamin B12 deficiency it can take up to six to 12 months to fully recover. It is also common to not experience any improvement during the first few months of treatment. Taking Vitamin B12 for losing weight is sometimes praised as a smart weight loss regimen but it s not fit to help everybody lose weight. The vitamin can counteract a natural deficiency in the body which when resolved can provide boosts in energy and metabolism. Vitamin B12 is a nutrient that helps keep your body s blood and nerve cells healthy and helps make DNA the genetic material in all of your cells.