Most vitamins are synthetic and hard to digest minerals. I worked at a vitamin store for 5 years and talked to a lot of the reps to find out how they were processed. Alot of vitamins will upset your stomach when taken on a empty stomach. Thats telling me that the digestive system is having to work too hard to break it down. Take 100mg of zinc on a empty stomach and it will upset it. Thats telling me its the mineral "form" is hard to digest because the size of the molecule is too large. Mined minerals are hard to absorb and are only 10-30% utilized. Most multi-vitamins seemed to cause too much stress on the digestive system.
However, High doses of vitamin C are a life saver when I need to quickly flush something/toxins out of my body. The only multi-vitamin brands I would take are garden of life, new chapter, and megalife. They are easier to digest.
High doses of any synthetic vitamin for long periods of time can cause imbalances in the body.