Vitamin B-12 Injections increase energy levels, helping to prevent fatigue. It can also help to suppress the appetite in weight loss programs. It stimulates the utilization of proteins, fats, and carbohydrates in the body. B12 is an essential water-soluble vitamin that is commonly found in a variety of foods such as fish, shellfish, meats, and dairy products. It helps maintain healthy nerve cells and red blood cells and is also needed to make DNA, the genetic material in all cells. B-12 injections should be given on a weekly basis (every 7-10 days) to maintain constant blood levels.