The amount of vitamin C you should take is the amount your body needs to stay healthy. This is determined by three factors: your genetic makeup, your environment and your current state of health. There is no clinical way to measure what this number is. It is something you have to determine on your own. The average adult would be well advised to take 8 to 10 grams of vitamin C per day. I personally take 16 grams. People with infections or chronic disease problems may need 40, 50 or even as much as 100 grams per day. Here is how to determine what your body needs: Gradually increase your vitamin C intake by one or two grams per day until you develop loose stools. Once this happens, back off to where this doesn’t happen. The rule of thumb is about 80 percent of where you were when the loose stools occurred. This amount is called "bowel tolerance. It is the amount your body needs, and what you should be taking.