Everything has a range of safety, which also means that there is a potential (however small) that enough could be taken to become harmful. For example, even water and sunlight, which are essential for life, can become harmful if taken in extremely large quantities or for too long a time. In the case of most vitamins, the amounts used in supplements have been shown in repeated studies to be very safe. But because there is the possibility of taking "too much of a good thing," it is important to discuss with your healthcare provider ALL supplements (and the amounts of each) you are taking, so your specific health goals can be properly met.